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Growth and characterization of lead-free ferroelectric (K,Na,Li)(Nb,Ta,Sb)O3 single crystal
... Therefore, we choose single crystal to carry out our study in this work. [22][23][24][25][26] In our previous work, large-sized high-quality KNNbased single crystals with different compositions have been successfully grown by top-seeded solution growth (TSSG) method, 5,10,12,16,17,27 which allowed us to carry out further research on domain configuration and corresponding electrical properties. It is known that the tetragonal crystal possesses a higher symmetry and simpler domain structure compared with orthorhombic one, thus we focus on tetragonal (K, Na, Li)(Nb, Ta, Sb)O 3 (KNLNTS) crystal in this work. ...
... The (K, Na, Li)(Nb, Sb, Ta)O 3 (KNLNTS) single crystal was grown by the top-seeded solution growth (TSSG) method. 27 In our previous work, we have measured the temperature dependence of dielectric constant for the KNLNTS crystals. It shows that the orthorhombic-tetragonal phase-transition temperature T O-T is À10°C and the Curie temperature T C is around 200°C. ...
... It shows that the orthorhombic-tetragonal phase-transition temperature T O-T is À10°C and the Curie temperature T C is around 200°C. 27 So in the temperature range from room temperature to 200°C, the KNLNST crystal is in tetragonal phase without phase transition. In this work we focus on the [011] C oriented samples. ...
E field and temperature dependent domain evolution of lead-free tetragonal (K, Na, Li)(Nb, Sb, Ta)O3 (KNLNTS) single crystals has been investigated as well as its corresponding electrical properties. When E field is applied along [011]C direction, (2T) engineered domain structure is formed. Spontaneous polarizations switch under a critical electric field (around 4-5 kV/cm), resulting in significant changes in domain structure and great improvement in piezoelectric properties. Further it is found that piezoelectric constant d31 and electromechanical coupling factor k31 of [011]C poled KNLNTS single crystal decrease with temperature. The extrinsic and intrinsic piezoelectric response are discussed from the view point of domain structure and lattice distortion respectively. Our results show that the nanodomain structure relaxes and the lattice distortion declines with temperature, resulting in reduction of exrinsic and intrinsic piezoelectric responses, respectively. Therefore the piezoelectric instability is ascribed to the decrease of both extrinsic and intrinsic contributions. This work provides a better understanding of domain engineering technique, and the useful information on the improvement of both piezoelectricity and temperature stability of the lead free piezoelectric materials. This article is protected by copyright. All rights reserved
... In our previous work, large-sized high quality KNN-based single crystals with different compositions have been grown by the topseeded solution growth (TSSG) method, which allowed us to carry out further research on domain configurations and extrinsic responses. [12][13][14][15][16] Above room temperature, KNN materials are either in the orthorhombic phase or tetragonal phase. Compared with orthorhombic phase, the domain structure of tetragonal phase is simpler due to its higher symmetry. ...
... e sd 11 and e sd 33 cannot be directly measured due to the lack of single domain sample. In another tetragonal KNN based single crystal, (K, Na, Li)(Nb, Ta)O 3 , the single domain state can be achieved, and the measured e sd 33 is around 240. Considering that the two crystals show similar phase transition temperature (T O-T ¼ 23 C, T C ¼ 197 C for (K, Na, Li)(Nb, Ta)O 3 and T O-T ¼ À10 C, T C ¼ À210 C for KNLNST), 14 and both crystals are stable in the tetragonal phase at room temperature, it is reasonable to assume that e sd 33 of KNLNST is around 240, then e sd 11 is calculated to be around 2904 through Eq. (4), and x should be 25.2% according to Eq. (5). Because e sd 33 is much smaller than e sd 11 , slight change of its value will not affect the conclusion. ...
Extrinsic contributions play an important role in the functionalities of ferroelectric materials, while domain structure evolution is crucial for understanding the extrinsic dielectric and piezoelectric responses. In this work, domain configuration changes with an electric field applied along [001]
C
in the tetragonal (K, Na, Li)(Nb, Sb, Ta)O3 single crystal were studied by means of polarizing light microscopy. Results show that parts of the spontaneous polarizations in the (001)
C
plane are switched to [001]
C
direction, while others still stay in the (001)
C
plane due to high induced internal stresses. Single domain state cannot be achieved even under a high electric field. After being poled along [001]
C
, the volume fraction of domains with polarzations in the (001)
C
plane is still about 25.2%. The extrinsic contributions to the dielectric constant are 15.7% and 27.2% under the E field of 1 kV/cm and under 2 kV/cm, respectively, estimated by the Rayleigh analysis.
... modifications of their physical properties [3,4]. However, considering the toxicity of lead and its compounds, there is a general awareness of the need for environmentally friendly lead-free materials [5][6][7]. In the search for lead-free alternatives, materials with the tetragonal tungsten bronze (TTB) structure are considered as attractive candidates thanks to their compositional flexibility, which is similar to the closely related perovskite structure [8][9][10][11][12][13][14]. ...
Tetragonal tungsten bronze (TTB) based oxides constitute a large family of dielectric materials which are known to exhibit complex distortions producing incommensurately modulated superstructures as well as significant local deviations from their average symmetry. The local deviations produce diffuse scattering in diffraction experiments. The structure as well as the charge dynamics of these materials are anticipated to be sensitive to defects, such as cation or oxygen vacancies. In this work, in an effort to understand how the structural and charge dynamical properties respond to these two types of vacancy defects, we have performed measurements of dielectric susceptibilities and single crystal diffraction experiments of two types of TTB materials with both ‘filled’ (Ba2NdFeNb4O15 and Ba2PrFeNb4O15) and ‘unfilled’ (Sr0.5Ba0.5Nb2O6) cation sublattices. We also perform these measurements before and after oxygen annealing, which alters the oxygen vacancy concentrations. Surprisingly, we find that many of the diffuse scattering features that are present in the unfilled structure are also present in the filled structure, suggesting that the random fields and disorder that are characteristic of the unfilled structure are not responsible for many of the local structural features that are reflected in the diffuse scattering. Oxygen annealing clearly affected both color and dielectric properties, consistent with a diminishment of the oxygen vacancy concentration, but had little effect on observed diffuse patterns.
... The rectangular shape indicates a considerably improved switching response with a sharp coercive field and a low degree of domain backswitching upon field removal. The resulting P r value is intriguingly much higher than those previously reported in crystals with similar compositions [20,36]. More details can be found in Fig. S1 and Table S1, Supporting Information. ...
Ferroelectric single crystals exhibit the largest known piezoelectric constants and therefore show high potential for application in electronic devices, including sensors, actuators, and transducers. Their large properties, however, can only be fully exploited if the behavior is not influenced by lattice defects, formed during high-temperature processing. Such defects can inhibit domain-wall movement, increase leakage currents, and are predominantly responsible for the poor performance of the emerging ferroelectric crystals. Here, an approach to considerably enhance the piezoelectric and ferroelectric properties of (K,Na,Li)(Nb,Ta,Sb)O3 crystals by oxygen annealing is investigated. As compared to the non-annealed crystals, polarization, strain, and piezoelectric constant of the annealed sample were enhanced by a factor of two, resulting in an outstanding room-temperature value of piezoelectric constant d33 = 732 pC/N and a peak value of d33 = 1431 pm/V at the orthorhombic-tetragonal transition. The behavior was analyzed using electromechanical measurements, Mössbauer spectroscopy, and impedance spectroscopy, revealing decreased concentrations of both oxygen vacancies and Sb³⁺ ions after annealing. The findings indicate that the control of the defect chemistry enables these ferroelectric (K,Na)NbO3-based single crystals to outperform their polycrystalline counterparts and reach the values of lead-containing compositions. Moreover, the present strategy enables further detailed studies of the inherent crystal anisotropy and the possibilities for domain engineering.
... The high leakage currents [23][24][25] and high dielectric losses, 26,27 probably induced by the volatilization of alkali elements, 28 the appearance of Nb 4þ ions, 29 and the segregation phenomena 30 during the crystal growth process, often prevent the detailed characterization of the electromechanical properties and stunt further development of KNN-based crystals. The partial substitution of Nb with Mn was reported to effectively suppress leakage currents. ...
Orientation and temperature dependence of dielectric and electromechanical properties of Mn-doped (Li,Na,K)(Nb,Ta)O3 single crystals were investigated. Samples exhibited very low dielectric losses, with tanδ between 0.03 and 0.05 over a broad temperature range between room temperature and 480 °C. Influences of the crystallographic structure and external electric field on polarization and strain parameters are discussed. The orientation-dependent electrical properties were ascribed to the anisotropic polarization rotation in the crystals. Higher maximum polarization, coercive field, and negative strain were achieved when the electric field was oriented along one of the spontaneous polarization directions. The highest maximum unipolar strain of 0.42% (at 3 kV/mm) and the normalized strain d 33 * of 1391 pm/V were obtained in the [001]PC-oriented sample at 100 °C, which was much higher than the values obtained for the [110]PC-oriented sample. Further insight of the phase transition behavior is given by comparing the temperature-dependence of the small- and large-signal dielectric and piezoelectric properties. The observed changes are rationalized by the different increase rates of the dielectric permittivity and piezoelectric coefficients with temperature.
High-temperature piezoelectric materials with good temperature stability are essential for various sensors fabrication. The monoclinic piezoelectric crystal α-BiB3O6 (BIBO) not only possess high resistivity, but also strong piezoelectric behaviors, promising...
As we all known that the piezoelectric single crystals exhibit unique and outstanding performance and therefore have been used widely in many electronic devices, including sensors, actuators, and transducers. Recently, large lead-free K0.5Na0.5NbO3(KNN)-based piezoelectric single crystals were prepared using a seed-free solid-state crystal growth (SFSSCG) method. However, there are some defects in the crystals prepared by this method. The defects would inhibit the domain-wall movement and increase the leakage currents in the crystals and then prevent the improvement of performance of the crystals. Here, an approach to considerably enhance the piezoelectric properties of the KNN-based crystals by annealing treatment is reported. The effect of the annealing temperature on the structure and electrical properties of the crystals was studied. The results show that the annealing temperature has a little effect on the crystalline structure but great effect on the natural surface morphology, domain structure, and electrical properties of the single crystals. When the annealing temperature is in the range of 550 ~ 800 °C, it can enhance significantly the piezoelectric, ferroelectric, and dielectric properties of the crystals and decrease their dielectric loss. The crystal annealed at 700 °C shows excellent properties: d33 = 591pC/N, εr = 580, tanδ = 0.01, kt = 0.715, and Tc = 417 °C. The effects of the annealing treatment on the leakage current density and conduction mechanism in the crystals were also studied. The results indicate that the annealing treatment enables the crystals to far outperform the unannealed crystals and comparable to the lead-based materials.
The forecasted restriction of lead containing materials in piezoelectric devices has created vast interest into the development of alternatives, i.e. lead-free systems. Since the discovery of improved properties, ferroelectric ceramics have dominated the commercial market for piezoelectric sensors, actuators and transducers. Relaxor ferroelectric single crystals are considered the premium piezoelectric materials, with high piezoelectric coefficients and low dielectric losses that enable them to be utilised in high-end applications, such as medical imaging ultrasounds. This review features the progress of lead-free single crystals that aim to replicate the remarkable piezoelectric properties that have been achieved in relaxor-PbTiO3 ferroelectric systems. Solid-state crystal growth (SSCG) has become a critical technique in the development of high-quality single crystals for such systems. SSCG is advantaged by its lower growth temperatures than conventional melt and solution growth techniques by producing crystals through a solid phase transformation of a polycrystalline matrix into a single crystal. This allows for higher chemical homogeneity and volatility control, while remaining a cost-effective growth method. The proposed theories of abnormal grain growth, which is the underlying mechanism that facilitates SSCG, will initially be discussed, followed by the challenges that must be controlled for continual high-quality single crystal growth. Given the correct polycrystalline microstructure and other processing parameters, large single crystals can be produced of incongruently melting systems that are unachievable using other techniques. This review provides a comparison of the state of the art of SSCG versus melt and solution growth techniques and concludes with the authors’ proposed focused points to inspire further improvements to both single crystal growth and piezoelectric properties.
Reducing or even prohibiting the usage of toxic lead in electronic devices has become one of the most cutting-edge topics in multi-discipline. The recently proposed phase boundary engineering endows lead-free piezoceramics with comparable performance to those of part lead-based ones. The enhanced performance hinges on the multi-phase coexistence and complex domain structure, particularly the occurrence of nano-domains and polar nanoregions (PNRs). Although nano-domains were largely studied in lead-based piezoceramics, understanding nano-domains and PNRs of lead-free piezoceramics is in infancy and needs a systematic summary and an in-depth analysis. Here we summarized nano-domains and PNRs of three representative lead-free piezoceramics (i.e., potassium sodium niobate, barium titanate, and sodium bismuth titanate), focusing on their effects on macro performance. Firstly, we introduced the foundation and observation tools of domains. Then, we summarized nano-domains varying with phase structure, electric field, and temperature, as well as their effects on performance including piezoelectricity, strain, temperature stability, aging, and fatigue. Finally, we gave out our perspectives on the future of nano-domains, concentrating on nano-domain engineering. Therefore, this review helps better understand the nano-domains and PNRs of lead-free piezoceramics and further develop high-performance lead-free piezoceramics.
Piezoelectric single crystals based on the perovskite ferroelectric system (K,Na)NbO3 have been widely investigated over the past 20 years due to large piezoelectric coefficients, high transition temperatures, low density, and the nontoxic chemical composition. Various crystal growth methods were examined, including high-temperature solution growth, solid-state crystal growth, Bridgman–Stockbarger method, and the floating zone method. Increased understanding of the crystal growth process and post-growth treatments resulted in improved crystal quality and larger sizes. Recently, crystals with high piezoelectric and electromechanical coupling coefficients exceeding 1000 pC/N and 0.90, respectively, were reported. Moreover, their large potential for high-frequency ultrasonic medical imaging was demonstrated. This work provides a review of the development of piezoelectric (K,Na)NbO3-based single crystals, including their growth, defect chemistry, domain structures, electromechanical properties, and applications. Approaches for reducing growth defects, controlling point defects, and domain engineering are discussed. The remaining open issues are presented and an outlook on the future is provided.
The phase structure, microstructure and electrical and electromechanical properties of ZnO-doped PbZr0.52Ti0.48O3 (PZT) ceramics were investigated. Piezoelectric ceramics were prepared by the conventional solid-state method. The XRD results indicate that it is the solid solution between the PZT and ZnO. SEM results indicate that the grain size increases and then excessive Zn ions concentrated in the grain boundaries of the ceramics and breaked grain boundaries. The addition of ZnO improved the Curie temperature, and It has a better temperature stability for 0.1 mol% doped PZT ceramics.
In this work, (K,Na,Li)(Nb,Ta,Sb)O3 (KNLNTS) crystal is in the orthorhombic phase at room temperature. The orthorhombic-tetragonal phase transition temperature is 50.0°C, and the Curie temperature TC of the tetragonal-cubic phase transition temperature is 253.8°C. The crystal is poled, the defects were “pinned” in specific position, and has positive effect in domain wall motions and better ferroelectric property (Pr is 6.49 µC/cm², Ec is 6.66 kV/cm). The domain configrations of the crystal were studied by means of a polarizing light microscopy (PLM), with poling along [100]C direction.
The monoclinic α-BiB3O6 (α-BIBO) crystal has been actively studied for nonlinear optical applications, but with limited efforts for piezoelectric usages. In this work, the temperature dependence of the electro-elastic properties for α-BIBO crystal was investigated over the temperature range of −150–150 °C, where the α-BIBO crystal was found to possess low dielectric loss (<0.5%) and minimal variation of relative dielectric permittivities (<±10%). The temperature coefficients of elastic compliances were obtained to be on the order of 0.2–5.1 × 10⁻⁴/°C. Moreover, the α-BIBO crystal was determined to own good temperature stability of electromechanical properties, with coupling factors being 13–32.1% at room temperature, while the independent piezoelectric coefficients shifted differently as a function of temperature with the first order temperature coefficients evaluated to be on the order of −0.3–17.9 × 10⁻⁴/°C. The above temperature characteristics of the electro-elastic properties are important for designing piezoelectric sensors operational over a broad temperature range.
A series of high-quality, large-sized (maximum size of 16 × 16 × 32 mm3) K1−xNaxTa1−yNbyO3 (x = 0.61, 0.64, and 0.70 and corresponding y = 0.58, 0.60, and 0.63) single crystals were grown using the top-seed solution growth method. The segregation of the crystals, which allowed for precise control of the individual components of the crystals during growth, was investigated. The obtained crystals exhibited excellent properties without being annealed, including a low dielectric loss (0.006), a saturated hysteresis loop, a giant piezoelectric coefficient d33 (d33 = 416 pC/N, determined by the resonance method and d33* = 480 pC/N, measured using a piezo-d33 meter), and a large electromechanical coupling factor, k33 (k33 = 83.6%), which was comparable to that of lead zirconate titanate. The reason the piezoelectric coefficient d33 of K0.39Na0.61Ta0.42Nb0.58O3 was larger than those of the other two crystals grown was elucidated through first-principles calculations. The obtained results indicated that K1−xNaxTa1−yNbyO3 crystals can be used as a high-quality, lead-free piezoelectric material.
Environmental friendly piezoelectric single crystal, Ta-modified (K,Na)NbO3 with the size of 12 6 11 6 11
mm3, has been successfully grown using the top seeded solution growth technique. This orthorhombic
phase (K,Na)(Nb,Ta)O3 single crystal is the largest size to date in KNN-based crystals with homogeneous
composition. The large size allowed us to apply the domain engineering technique to further enhance its
piezoelectric properties. In addition, a self-consistent complete set of elastic, dielectric and piezoelectric
constants for the [001]c poled domain engineered crystal has been measured, which is urgently needed for
theoretical studies and simulation designs of electromechanical devices using this lead-free piezoelectric
material. The electromechanical coupling factors are very high (k33 = 0.827, kt = 0.646) and the dielectric
loss tangent is as low as 0.004 for this lead-free piezoelectric crystal. Such excellent properties make this
crystal an excellent candidate to replace lead-containing piezoelectric materials in electromechanical
devices.
Domain structures and their evolution with temperature in the [001] C oriented (K,Na)(Nb,Ta)O3 (KNNT) single crystal have been studied before and after poling by polarizing light microscopy. The results indicate that the KNNT crystal is difficult to be completely poled by the room temperature poling process. The domain structure is rather stable in the orthorhombic phase, but exhibits substantial changes near the phase transition temperatures T O-T and T C. Narrower stripe domains are formed during both the orthorhombic-tetragonal and tetragonal-cubic phase transition processes, no intermediate phases were found during the phase transitions. The temperature dependence of the dielectric and piezoelectric properties were measured, and the influence of domain structures on the dielectric and electromechanical properties were quantified.
The complete set of material constants of single domain rhombohedral phase 0.27Pb(In1/2Nb1/2)O3-0.46Pb(Mg1/3Nb2/3)O3-0.27PbTiO3:Mn single crystal has been determined. The orientation dependence of piezoelectric, dielectric, and electromechanical properties was calculated based on these single domain data. The maximum piezoelectric and electromechanical properties were found to exist near the [001]C pseudo-cubic direction. In addition, the piezoelectric properties of [001]C poled crystals with “4R” multi-domain configuration were experimentally measured and compared with the calculated values. Only a small difference (3%) was found between experimental and theoretical values, indicating the high piezoelectric properties in the “4R” state are mainly from intrinsic contributions. The mechanical quality factors Q33 are significantly improved by the Mn-doping for the “4R” domain engineered crystals but almost no change for the single domain “1R” state. On the other hand, Q15 of both single domain and multidomain crystals were found to increase with Mn-doping, due to the internal bias induced by acceptor dopants, which clamps the domain wall motions and restricts polarization rotation.
BaTiO3 (BT) nanocrystals were synthesized by a hydrothermal method at 220°C, and their crystal structure, morphology, and surface structure were characterized by X-ray diffraction (XRD), Raman spectroscopy, scanning electron microscopy (SEM), transmission electron microscopy (TEM), and high-resolution TEM (HRTEM), respectively. The results of XRD and Raman spectroscopy indicated that the BT nanocrystals are of tetragonal phase at room temperature. SEM and TEM images showed that the larger Ba/Ti molar ratios in the precursors led to the formation of larger nanocrystals with a cubic morphology. HRTEM images revealed that the cubic nanocrystals were bound by their {100} faces. A core–shell surface structure was observed in the nanocrystals, where the shell layer was cubic with a thickness in the range 2–3.5nm, and the core was a bulk tetragonal. The interface structure between the shell and the core was coherent without any interfacial dislocation. At rough edges of the nanocrystals, their {110} edges were faceted by {100} planes in a form of few atomic layers wide steps, showing some degree of ledge-kink reconstruction. These microstructural results enable ones to achieve nanocrystals with controlled size and morphology.
Synchrotron x-ray powder diffraction measurements have been performed on unpoled ceramic samples of (1-x)Pb(Mg1/3Nb2/3)O-3-xPbTiO(3) (PMN-xPT) with 30%less than or equal toxless than or equal to39% as a function of temperature around the morphotropic phase boundary, which is the line separating the rhombohedral and tetragonal phases in the phase diagram. The experiments have revealed very interesting features previously unknown in this or related systems. The sharp and well-defined diffraction profiles observed at high and intermediate temperatures in the cubic and tetragonal phases, respectively, are in contrast to the broad features encountered at low temperatures. These peculiar characteristics, which are associated with the monoclinic phase of M-C-type previously reported by Kiat [Phys. Rev. B 65, 064106 (2000)] and Singh and Pandey [J. Phys. Condens Matter 13, L931 (2001)], can only be interpreted as multiple coexisting structures with M-C as the major component. An analysis of the diffraction profiles has allowed us to properly characterize the PMN-xPT phase diagram and to determine the stability region of the monoclinic phase, which extends from x=31% to x=37% at 20 K. The complex lansdcape of observed phases points to an energy balance between the different PMN-xPT phases which is intrinsically much more delicate than that of related systems such as PbZr1-xTixO3 or (1-x)Pb(Zn1/3Nb1/3)O-3-xPbTiO(3). These observations are in good accord with an optical study of x=33% by Xu [Phys. Rev. B 64, 020102 (2001)], who observed monoclinic domains with several different polar directions coexisting with rhombohedral domains, in the same single crystal.
Lead-free piezoelectric ceramics (1-x-y)Bi{sub 0.5}Na{sub 0.5}TiO{sub 3}-xBaTiO{sub 3}-yK{sub 0.5}Na{sub 0.5}NbO{sub 3} (0.05{<=}x{<=}0.07 and 0.01{<=}y{<=}0.03), have been synthesized by a conventional solid state sintering method. The room temperature ferroelectric and piezoelectric properties of these ceramics were studied. Based on the measured properties, the ceramics were categorized into two groups: group I compositions having dominant ferroelectric order and group II compositions displaying mixed ferroelectric and antiferroelectric properties at room temperature. A composition from group II near the boundary between these two groups exhibited a strain as large as {approx}0.45% at an electric field of 8 kV/mm. Polarization in this composition was not stable in that the piezoelectric coefficient d{sub 33} at zero electric field was only about 30 pm/V. The converse piezoelectric response becomes weaker when the composition deviated from the boundary between the groups toward either the ferroelectric or antiferroelectric compositions. These results were rationalized based on a field induced antiferroelectric-ferroelectric phase transition.
Mn modified 0.26Pb(In(1/2)Nb(1/2))O(3)-0.42Pb(Mg(1/3)Nb(2/3))O(3)-0.32PbTiO(3) (PIN-PMN-PT:Mn) single crystals with orthorhombic perovskite crystal structure were polarized along [011] direction, resulting in the single domain state "1O." The complete set of material constants was determined using the combined resonance and ultrasonic methods. The thickness shear piezoelectric coefficient d(15) and electromechanical coupling factor k(15) were found to be on the order of 3100 pC/N and 94%, respectively, much higher than longitudinal d(33) ∼ 270 pC/N and k(33) ∼ 70%. Using the single domain data, the rotated value of d(33)* along [001] direction was found to be 1230 pC/N, in agreement with the experimentally determined d(33) value of 1370 pC/N, conferring extrinsic contributions being about 10%, which was also confirmed using the Rayleigh analysis. In addition, the mechanical quality factors Q(m) were evaluated for different "1O" vibration modes, where the longitudinal Q(m) was found to be ∼1200, much higher than the value for "4O" crystals, ∼300.
Lead-free piezoelectric ceramics, with the nominal composition of 0.948( K <sub>0.5</sub> Na <sub>0.5</sub>) Nb O <sub>3</sub>–0.052 Li Sb O <sub>3</sub> (KNN-LS5.2), were synthesized by conventional solid-state sintering, and the piezoelectric and electromechanical properties were characterized as a function of temperature. The Curie temperature of the KNN based perovskite material was found to be 368 ° C with an orthorhombic-tetragonal polymorphic phase transition (T<sub>O-T</sub>) temperature at approximately ∼35 ° C . The room temperature dielectric permittivity (ε<sub>33</sub><sup>T</sup>/ε<sub>0</sub>) and loss were found to be 1380 and 2%, respectively, with piezoelectric properties of k<sub>33</sub>∼62% and d<sub>33</sub>∼265 pC / N and k<sub>31</sub>∼30% and d<sub>31</sub>∼-116 pC / N . The temperature dependence of the properties mimicked the compositional variation seen in the proximity of a morphotropic phase boundary [e.g., lead zirconate titanate (PZT)], with a maxima in the dielectric and piezoelectric properties and a corresponding “softening” of the elastic properties. Unlike that found for PZT-type materials, the modified KNN material exhibited characteristics of both “soft” and “hard” piezoelectricities owing to the distinctly different domain states associated with orthorhombic and tetragonal phases.
Large thickness coupling factors k<sub>T</sub>≤0.7 are measured in both [001]<sub>C</sub> -oriented (45° cut in the orthorhombic ac plane), monodomain and [001]<sub>C</sub> -poled, domain-engineered single crystals of K Nb O <sub>3</sub> . k<sub>T</sub> is extremely stable over a large temperature range, remaining high (≥0.65) even upon heating and cooling through the orthorhombic-tetragonal phase transition. This is likely related to another finding that spontaneously high k<sub>T</sub> values (≤0.68) are observed in as-grown (unpoled), [001]<sub>C</sub> -cut, polydomain K Nb O <sub>3</sub> crystals. k<sub>T</sub> is also stable upon thinning to thicknesses below 60 μ m , as required for high-frequency applications. Finally, large k<sub>T</sub> values (≤0.7) are reported in [001]<sub>C</sub> -poled, polydomain, Li-doped ( K <sub>0.5</sub> Na <sub>0.5</sub>) Nb O <sub>3</sub> .
In addition to x-ray diffraction, Raman spectrum measurements provide direct evidence of the tetragonal and orthorhombic phases coexistence in lead-free ceramics (1-x) K <sub>0.5</sub> Na <sub>0.5</sub> Nb O <sub>3</sub> ( KNN )–x Li Ta O <sub>3</sub> when x equals 5 mol % . This is caused by the phase transition temperature between tetragonal and orthorhombic decreasing to around room temperature due to the Li and Ta doping in KNN, and not by constituting a region of morphotropic phase boundary as presented by most published papers. The results indicate that although this kind of ceramic displays good properties, it needs further study to verify if it is suitable to be used in a varying temperature environment.
Relaxor-PT based ferroelectric single crystals Pb(Zn<sub>1/3</sub>Nb<sub>2/3</sub>)O<sub>3</sub>-PbTiO<sub>3</sub> (PZNT) and Pb(Mg<sub>1/3</sub>Nb<sub>2/3</sub>)O<sub>3</sub>-PbTiO<sub>3</sub> (PMNT) offer high performance with ultra-high electromechanical coupling factors k33s > 0.9 and piezoelectric coefficients d<sub>33</sub>s > 1500 pC/N. However, the usage temperature range of these perovskite single crystals is limited by TRT-the rhombohedral to tetragonal phase transition temperature, which occurs at significantly lower temperatures than the Curie temperature T<sub>C</sub>, a consequence of curved morphotropic phase boundaries (MPBs). Furthermore, these 〈001〉-oriented crystals exhibit low mechanical quality Q and coercive fields, restricting their usage in high-power applications. In this survey, recent developments on binary and ternary perovskite relaxor-PT crystal systems are reviewed with respect to their temperature usage range. General trends of dielectric and piezoelectric properties of relaxor-PT crystal systems are discussed in relation to their respective T<sub>C</sub>/T<sub>RT</sub>. In addition, two approaches have been implemented to improve mechanical Q, including acceptor dopants, analogous to hard polycrystalline ceramics, and anisotropic domain engineering, enabling lowloss crystals with high coupling for high-power applications.
Li, Ta modified (K,Na)NbO3 single crystals with the size of 18 mm × 18 mm × 10 mm were successfully grown by top‐seeded solution growth method, with orthorhombic–tetra‐gonal phase transition temperature ∼79 °C and Curie temperature ∼276 °C. The electromechanical coupling factors k 33 and k t were found to be ∼88% and ∼65%, respectively. The piezoelectric coefficient d 33 for the [001]c poled crystals reached 255 pC/N. In addition, the electromechanical coupling factor exhibited high stability over the temperature range of –50 °C to 70 °C, making these lead free crystals good candidates for electromechanical applications. (© 2014 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim) This Letter presents Li, Ta modified (K, Na)NbO3 single crystals with the size of 18 mm × 18 mm × 10 mm grown by top‐seeded solution growth method. Of particular importance is that the electromechanical coupling factor k 33 was found to be ∼88% and exhibited good thermal stability up to the orthorhombic–tetragonal phase transition temperature, making these lead free crystals good candidates for piezoelectric applications.
(1-x)(Bi0.5Na0.5)TiO3-xBa(Zr0.055Ti0.945)O3 (0 ≤ x ≤ 0.12) lead-free ceramics have been prepared and the morphotropic phase boundary (MPB) is confirmed to be x = 0.06–0.09. The MPB composition x = 0.07 shows enhanced pyroelectric properties from room temperature (RT) to the depolarization temperature Td (87 °C), with the pyroelectric coefficient p = 0.057 μC/cm2 °C and the figures of merit Fi = 203 pm/V, Fv = 0.022 m2/C, and Fd = 10.5 μPa-1/2 at RT and the highest pyroelectric coefficient of 2.21 μC/cm2 °C near Td. These values are superior to other lead-based/lead-free pyroelectric ceramics. Enhanced pyroelectric properties can be explained by the effects of MPB and ferroelectric-antiferroelectric phase transition.
Single crystals of relaxor ferroelectric-based (1- x)Pb(Zn
1/3Nb 2/3)O 3- xPbTiO 3 [or
PZNT(1- x)/ x] solid solution system (with x=4.5%, 6%, 7%, 10%, 12% and
15%) have been grown from PbO flux by a top seeded solution growth
(TSSG) technique. The saturation-growth temperature ( Ts) and
the appropriate cooling rate (0.5-1°C/h) at Ts were
determined for each composition. Ts indicates the temperature
at which a seed crystal can effectively grow from the flux. Under
optimum conditions with a solute/solvent ratio PZNT/PbO=1 : 1 (in
weight), or a 50 wt% of flux ratio, perovskite PZN-PT crystal boules of
35 mm diameter and 14 mm height were successfully grown using a crucible
of 50 ml (∅=40 mm). The dielectric and ferroelectric properties of
the grown crystals were characterized and the crystal quality assessed.
The TSSG technique developed in this work provides an alternative route
to the growth of medium to large size PZN-PT crystals for a wide range
of applications in electro-mechanical transduction.
We have grown by flux method centimeter-sized single crystals from pseudo-hexanary Li2O–Na2O–K2O–Nb2O5–Ta2O5–Sb2O3 system. Based on chemical analysis, crystals of compositions (Li0.023Na0.583K0.394)(Nb0.925Ta0.037Sb0.038)O3 and (Li0.034Na0.609K0.357)(Nb0.896Ta0.047Sb0.057)O3 were characterized by X-rays diffraction which revealed a tetragonal structure. The dielectric analysis confirmed that the ferroelectric behavior of these crystals is very sensitive to little changes in composition as previously observed on ceramics. Such high flexibility of the ferroelectric properties in crystals opens the way towards improved understanding of the relations between structure and polarization in solid solutions which may be an alternative to the lead-based materials.RésuméDes monocristaux centimétriques issus du système Li2O–Na2O–K2O–Nb2O5–Ta2O5–Sb2O3 ont été obtenus par la méthode des flux. Les cristaux de composition (Li0.023Na0.583K0.394)(Nb0.925Ta0.037Sb0.038)O3 et (Li0.034Na0.609K0.357)(Nb0.896Ta0.047Sb0.057)O3 ont été caractérisés par diffraction des rayons X et se sont avérés appartenir au système quadratique. Leur comportement ferroélectrique spécifique a été confirmé par des mesures diélectriques. Une telle flexibilité des propriétés ferroélectriques de ces cristaux pour de faibles variations de composition ouvre la voie vers une meilleure compréhension des relations entre la structure et la polarisation dans ces solutions solides, qui sont potentiellement une alternative aux matériaux contenant du plomb.
Na0.5K0.5NbO3 (NKN) and Mn-doped NKN crystals, which are one of the promising candidates of lead-free piezoelectric materials, were grown by using a floating zone (FZ) method. The resulting crystal growth was compared with crystal growth that resulted from using a flux method in a previous study. In the crystal grown by FZ method under where the growth rate was controlled to 3 mm/h, thin layers formed parallel and perpendicular directions to the growth direction. In the crystal grown by FZ method, the crystal structure could not be classified as having the orthorhombic lattice of Amm2, which was observed in the crystal grown using a flux method. It was found that doped Mn was substituted in the perovskite-type lattice of NKN. Pure NKN crystals showed 90° domains that had a zig-zag shape, whereas Mn-doped NKN crystals were aligned to the domain layers in straight lines. It was confirmed that Mn-doped NKN crystal showed a square P–E hysteresis loop.
Relaxor-based ferroelectric single crystal xPb(In1/2Nb1/2)O3–yPb(Mg1/3Nb2/3)O3–(1−x−y)PbTiO3 {PIMNT [100x/100y/100(1−x−y)]} has been grown by the modified Bridgman technique. The as-grown PIMNT (21/49/30) crystal with a rhombohedral perovskite-type structure shows high phase transition temperature from ferroelectric rhombohedral to tetragonal (TRT∼125°C) and high Curie temperature (TC∼180°C), about 50°C higher than what was found for the 0.71Pb(Mg1/3Nb2/3)O3–0.29PbTiO3 [PMNT (71/29)] crystal. Moreover, as a core parameter of the pyroelectric material, the detectivity figures-of-merit of the PIMNT (21/49/30) crystal is 14.2×10−5Pa−1/2, higher than that of other typical relaxor-based ferroelectric crystals, which primarily stems from the low dielectric loss, making it a promising candidate for the next generation of high performance infrared detectors.
An optical, dielectric, and structural study has been carried out on NaNbO3 and the solid solution (Na,K)NbO3, both single crystals and ceramics being used. No evidence for ferroelectricity in NaNbO3 was found, and the crystal seems to be antiferroelectric in accordance with the nonpolar structure reported by Vousden. It is shown that a small addition of KNbO3 to pure NaNbO3 produces a new ferroelectric phase, the existence of which suggests a possible explanation of the conflicting dielectric and structural properties previously reported. The phase diagram of NaNbO3-KNbO3 is given. This, together with the optical and x-ray studies of pure NaNbO3, shows that the three phase transitions in NaNbO3 are quite different in nature from the BaTiO3-type transitions in KNbO3.
Nanopowders of the lead-free ceramic system (K0.5−xLixNa0.5)(Nb0.9Ta0.1)O3 (KNN) with x=0, 0.015, 0.045, and 0.060 have been synthesized by conventional solid state reaction followed by high-energy ball milling. The average particle size of all the milled powders as determined from the TEM analysis was about 35nm. These powders were sintered at 1050°C for 4h. Analysis of all the ceramic samples using X-ray diffraction method showed single-phase perovskite structure with orthorhombic symmetry. The effects of the Li substitution on the structural, dielectric, and ferroelectric properties of the ceramics were systematically studied. Without any sintering aid such as ZnO, MnO2 and CuO, densities ≥95% of the theoretical density of the KNN ceramics has been achieved. The SEM analysis of fractured surfaces of the ceramics indicates that the fractures occur mostly within the grains. An increase in Li substitution in the KNN ceramics produced an increase in the Curie temperature (Tc) and a decrease in the coercive field (Ec). In the range of Li contents studied, the sample with x=0.015 possessed the highest values in the density, orthorhombic–tetragonal transition temperature (Tot), dielectric constant (ɛ′), and remnant polarization (Pr).
There has been a significant driving force to eliminate the utilization, recycling, and disposal of ferroelectric ceramics
with high content of toxic element (Pb). Recently, the ternary system of KNN-LT-LS has proven to be an outstanding lead-free
piezoceramic with properties almost comparable to their lead-based counterpart, PZT. This study reports the effect of various
processing conditions on the electromechanical properties of (K0.44Na0.52Li0.04)(Nb0.84Ta0.10Sb0.06)O3 system. This includes powder processing, humidity, and exposure to oxygen rich environment during sintering. The Perovskite
and Mixed-Oxide methods are used to prepare the stoichiometric powders. It will be shown that both processing methods are
notably sensitive to the moisture of as received raw materials and the humidity of environment. Optimum results are obtained
when the raw materials undergo a pre-heat treatment followed by formulating the desired composition in an inert atmosphere.
The highest electromechanical properties are achieved when the ceramics are completely exposed to oxygen with a high flow
rate. Sintered at 1150 °C for 1 h with an oxygen flow rate of 180 cm3/min, the KNN-LT-LS ceramics prepared by Perovskite and Mixed-Oxide routes have d
33 ≥ 300 pC/N, $$\varepsilon ^{T}_{{33}} = 1865$$, tan δ = 0.02, k
33 = 0.65.
Lead calcium titanate ceramics modified by partial substitution of rare earths for lead, particularly, (Pb, Sm, Ca)(Ti, Mn)O(3) ceramics, were explored for their structural, dielectric and piezoelectric properties. These modified ceramics with a composition of Pb(0.76-3x/2)Sm(x)Ca(0.24)Ti(0.98)Mn(0.02)O(3) (x = 0 - 0.08) were prepared by solid state reaction route. The XRD study showed single-phase formation with tetragonal structure. Lattice anisotropy (c/a) was found to decrease from 1.057 to 1.023 with increase in Sm substitution from 0 to 8 mol%, respectively. Microstructural study revealed the average grain size between 1.2 and 2.2 mu m. The relative density was found to increase from 95% to 98.4% with increase in samarium substitution from 0 to 8 mol%, respectively. Detailed dilatometric study was performed in order to study the shrinkage behaviour during the sintering schedule. The maximum shrinkage was found to occur between 900 degrees C and 1100 degrees C. The dielectric constant (epsilon') and loss (tan delta) for all the compositions were investigated over a wide frequency (100 Hz to 1 MHz) and temperature (25-450 degrees C) range. The room temperature (25 degrees C) dielectric constant was found to increase from 130 (at 10 kHz) for pure lead calcium titanate sample to 380 (at 10 kHz) for 8 mol% samarium substituted sample and also showed a decreasing trend with increase in the frequency for all the substitutions (0-8 mol% Sm). Curie temperature, T
(K0.5Na0.5)NbO3 (KNN) single crystals were grown using a high temperature flux method. The dielectric permittivity was measured as a function of temperature for [001]-oriented KNN single crystals. The ferroelectric phase transition temperatures, including the rhombohedral–orthorhombic TR−O, orthorhombic–tetragonal TO−T and tetragonal–cubic TC were found to be located at −149 ∘C, 205 ∘C and 393 ∘C, respectively. The domain structure evolution with an increasing temperature in [001]-oriented KNN single crystal was observed using polarized light microscopy (PLM), where three distinguished changes of the domain structures were found to occur at −150 ∘C, 213 ∘C and 400 ∘C, corresponding to the three phase transition temperatures.
Compositions in the system KNbO3-NaNbO2 have been hot-pressed to yield ceramics with relative densities greater than 99%. Because these materials lack any degree of pyroplastic behavior, temperatures approaching those required for air sintering are needed. These hot-pressed specimens exhibit a finer microstructure than that obtainable by conventional processing. Enhanced piezoelectric coefficients are observed, and in certain compositional regions radial coupling coefficients have been increased from 32 to approximately 48%. Dielectric constants increase with densification and ac losses remain relatively high. The fine structure and improved piezoelectric activity, especially near the equimolar composition, make these materials desirable for electromechanical transducers, particularly in the 10 to 20 Mc per second range. The rate equation of Murray, Live, and Williams for hot-pressing ceramics was found to apply in this system.
The microstructure and electrical properties of calcium‐modified barium titanate ceramics of compositions (Ba 1-x Ca x )TiO 3 have been investigated. From the influence of the CaO content and stoichiometry on the said characteristics of the materials, it is concluded that the cationic ratio, α=(Ba+Ca)/Ti, is the predominant factor affecting the resistance of materials against the reducing sintering atmosphere. The electrical properties, including resistivity and dielectric dispersion, can be completely preserved when the sintering atmosphere is switched from air to H 2 /N 2 , but only for samples with values of α greater than unity. The formation of a hexagonal BaTiO 3-δ phase, which consumes the oxygen vacancies, is presumed to be the factor that improves the resistance of these materials against the reducing sintering atmosphere.
Lead-free potassium sodium niobate piezoelectric single crystals substituted with lithium 0.95( K <sub>0.5</sub> Na <sub>0.5</sub>) Nb O <sub>3</sub>–0.05 Li Nb O <sub>3</sub> have been grown by Bridgman method and their dielectric and piezoelectric properties were studied. The orthorhombic-tetragonal and tetragonal-cubic phase transition temperatures of the single crystal appear at 192 and 426 ° C according to the dielectric constant versus temperature loops, respectively, and the (001) plates show good piezoelectric properties with piezoelectric constant d<sub>33</sub> as high as 405 pC / N , large thickness electromechanical coupling factor k<sub>t</sub>=61% , and low dielectric constant of 185 at room temperature. These excellent properties show that the 0.95( K <sub>0.5</sub> Na <sub>0.5</sub>) Nb O <sub>3</sub>–0.05 Li Nb O <sub>3</sub> single crystal is a good lead-free piezoelectric material.
Leakage current properties of K <sub>0.5</sub> Na <sub>0.5</sub> Nb O <sub>3</sub> (KNN) single crystals grown by a flux method have been investigated to establish a guiding principle of defect control for high-performance lead-free piezoelectric devices. The substitution of Mn at the Nb site and the following annealing under moderate oxidation condition was effective for suppressing leakage current of KNN crystals. Electron spin resonance measurements demonstrate that oxidation of Mn during annealing plays an essential role in low leakage current in the KNN system. Mn-doped KNN crystals exhibited a low leakage current density (∼10<sup>-8</sup> A / cm <sup>2</sup>) and relatively large remanent polarization of 40 μ C / cm <sup>2</sup> at 25 ° C .
The dielectric, ferroelectric, piezoelectric, and electrostrictive properties of K <sub>0.5</sub> Na <sub>0.5</sub> NbO <sub>3</sub> single crystals (KNN s.c.) prepared by solid-state crystal growth are reported. The dielectric constant (ε) , dielectric losses ( tan δ) , remanent polarization ( P <sub> r </sub>) , and coercive field ( E <sub> c </sub>) for KNN s.c. in the [1 3 1] direction at room temperature are 1015, 1%, 17 μ C / cm <sup>2</sup> , and 24 kV/cm, respectively. The influence of 180° domains to the linear piezoelectric response and quadratic electrostrictive response of KNN s.c. is discussed. The piezoelectric coefficient d <sub>33</sub> and the electrostrictive coefficient M <sub>33</sub> of KNN s.c. measured using atomic force microscopy at 2 Hz was 80 pm/V and 2.59×10<sup>-14</sup> m <sup>2</sup>/ V <sup>2</sup> , respectively. The extremely high M <sub>33</sub> value can be explained by the extrinsic strain from the domain-wall motion. The properties of the surrounding polycrystalline KNN ceramic are added for comparison.
(K0.5Na0.5)NbO3 (KNN) based lead free ceramics have been fabricated by a solid state reaction. In this work, LiSbO3 (LS) modified KNN based ceramics were sintered at atmospheric pressure and high density (>96% theoretical) was obtained. The detailed elastic, dielectric, piezoelectric and electromechanical properties were characterized by using the resonance technique combined with the ultrasonic method. The full set of material constants for the obtained polycrystalline ceramics were determined and compared to the pure hot pressed KNN counterpart. KNN-LS polycrystalline ceramic was found to have higher elastic compliance, dielectric permittivity and piezoelectric strain coefficients, but lower mechanical quality factor, when compared to pure KNN, exhibiting a “softening” behavior. However, a high coercive field (∼17 kV/cm) was found for the LS modified KNN material. The properties as a function of temperature were determined in the range of −50–250 ∘C, showing a polymorphic phase transition near room temperature, giving rise to improved piezoelectric behavior.
Lead has recently been expelled from many commercial applications and materials (for example, from solder, glass and pottery glaze) owing to concerns regarding its toxicity. Lead zirconium titanate (PZT) ceramics are high-performance piezoelectric materials, which are widely used in sensors, actuators and other electronic devices; they contain more than 60 weight per cent lead. Although there has been a concerted effort to develop lead-free piezoelectric ceramics, no effective alternative to PZT has yet been found. Here we report a lead-free piezoelectric ceramic with an electric-field-induced strain comparable to typical actuator-grade PZT. We achieved this through the combination of the discovery of a morphotropic phase boundary in an alkaline niobate-based perovskite solid solution, and the development of a processing route leading to highly <001> textured polycrystals. The ceramic exhibits a piezoelectric constant d33 (the induced charge per unit force applied in the same direction) of above 300 picocoulombs per newton (pC N(-1)), and texturing the material leads to a peak d33 of 416 pC N(-1). The textured material also exhibits temperature-independent field-induced strain characteristics.
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