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Structural, dielectric, ferroelectric and strain properties in CaZrO3-modified Bi(Mg0.5Ti0.5)O-3-PbTiO3 solid solutions
... This indicated that the Co +3 and Nb +5 ions replaced Ti 4+ at the B-site of the perovskite unit cell. Due to the relatively larger ionic radii of Co 3+ (0.745Å) and Nb 5+ (0.64Å) compared to Ti 4+ (0.605Å) at the B-site, the substituent (Co 0.5 Nb 0.5 ) 4+ ions generated lattice expansion, which then corresponded with the peak positions by shifting toward a lower angle [38][39][40][41][42]. ...
High strain with low hysteresis is crucial for commercial applications in high precision actuators. However, the clear conflict between the high strain and low hysteresis in BNT-based ceramics has long been an obstacle to actual precise actuating or positioning applications. To obtain piezoceramics with high strain and low hysteresis, it is necessary to enhance the electrostrictive effect and develop an ergodic relaxor (ER) and nonergodic relaxor (NR) phase boundary under ambient conditions. In this work, (Co0.5Nb0.5)4+ doped 76Bi0.5Na0.5TiO3-24SrTiO3 (BNST24) relaxors were fabricated using the conventional solid state reaction route. X-ray diffraction patterns revealed the B-site substitution in BNST24 ceramics. By adjusting the (Co0.5Nb0.5)4+ doping in BNST24, we effectively tuned the TNR-ER and Td close to ambient temperature, which contributed to the development of the ergodic relaxor phase and enhanced the electrostrictive effect at ambient temperature. The I-P-E loops and bipolar strain curves verified the gradual evolution from NR to ER states, while the enhanced electrostrictive effect was verified by the nearly linear S-P2 curves and improved electrostrictive coefficient of the BNST24-xCN relaxors. An enhanced strain of 0.34% (d*33 = 483 pm/V) with low hysteresis of 8.9% was simultaneously achieved in the BNST24-0.02CN relaxors. The enhanced strain was mainly attributed to the proximity effect at the ER and NR phase boundary of BNST24-0.02CN, while the improved electrostrictive effect contributed to the reduced strain hysteresis. Our work demonstrates an effective strategy for balancing the paradox of high strain and low hysteresis in piezoceramics.
... Such a change is mainly attributed to the reduction in negative strain (S neg ), which can be observed in bipolar and unipolar strain loops, and the S neg of the sample with x = 0.12 become zero at 150°C. Notable S neg is a typical feature of long-range ferroelectric order, the vanishing of S neg is considered as evidence of disappearance of long-range ferroelectric order and appearance of ergodic relaxors [42,43] Thus the decrease of S neg is primarily caused by the transition from long-range ordered ferroelectric to ergodic state [44], and we can conclude that the ferroelectric-ergodic transition temperature in Mn-doped PINT ceramics are lower than that of virgin PINT ceramic. The temperature dependent high-field strain coefficient d* 33 calculated from the slope of strain-electric field is displayed in Fig. S3 (see Supplementary Material). ...
Thermal stability of piezo-/ferro-electric properties of ferroelectrics is important for the devices working at elevated temperature. A study on thermal stability of ferroelectrics will be greatly helpful for future applications. In this work, thermal behaviors of electrical properties were studied in Mn-doped Pb(In1/2Nb1/2)O3-PbTiO3 (PINT) ceramics. The ferroelectric hysteresis loops of Mn-doped samples change anomalously with increasing temperature compared with the virgin sample. Remnant polarization of PINT ceramics with high manganese content (x ≥ 0.04) exhibits increase trend as temperature increasing, leading to a negative electrocaloric effect which was reported to be beneficial to improving the cooling efficiency. For Mn-doped PINT ceramics, the reduction rate of coercive field reaches a relatively low value of 3%, indicating outstanding ability of depolarization resistance. PINT ceramics with proper dopant concentration show improved aging resistance and thermal stability of piezoelectric property after annealed. Out-of-plane domain configurations show different features at room temperature and elevated temperatures.
... Therefore, S neg can be regarded as an estimation of ferroelectricity contribution in ferroelectrics [25]. Here, the large value of S neg in Mn-doped samples suggests that the introduction of Mn promotes the occurrence of ferroelastic domain structure, and increases the degree of long-range ferroelectric order [26]. Consequently, the improved S neg also implies enhanced ferroelectricity in Mnmodified 0.72BFO-0.28BCZT ...
Manganese-modified BiFeO3-based ceramics with typical perovskite structure were fabricated by solid-state reaction method with non-quenched processing. The effects of Mn addition on ferroelectric, strain, magnetic properties as well as domain structure were intensively investigated. The average negative strain significantly increased from ∼0.02% to ∼0.10% after Mn incorporation. Piezoresponse force microscope (PFM) analysis revealed that Mn ions can tune ferroelectric domain heavily, and increase the amount of non-180° ferroelectric domain. Raman spectra demonstrated that the formation of ferroelectric domain and enhanced magnetic properties mainly resulted from the strengthened distortion of octahedral due to Mn addition. Our work provides a better understanding of the correlation between the domain structure and macro-properties in Mn-modified BFO-based multiferroic ceramics.
... It is also reflected with the merging of peaks in XRD that indicate from non-centrosymmetric to centrosymmetric structure. Again we need to mention that for tolerance factor ~1, a perovskite phase is expected [16,17]. The tolerance factor of the PNST-x samples decreases from 1.019 as in x = 0 to 0.988 for x = 0.5 (Table 1). ...
A correlation between structure and vibrational properties related to a ferroelectric to paraelectric phase transition in perovskite Pb(1-x)(Na0.5Sm0.5)xTiO3 (PNST - x) polycrystalline powders is discussed. Substitution leads to reduction of tetragonality which is associated with a shift of the phase transition to lower temperatures. The nature of the phase transition gets diffused with increasing substitution.
High‐performance piezoelectric materials are essential in many piezoelectric devices. However, the composition of piezoelectric materials usually has a great influence on their performance. In this work, x Bi(Mg 1/2 Ti 1/2 )O 3 – y PbZrO 3 – z PbTiO 3 ( x BMT– y PZ– z PT; 0.2 ≤ x ≤ 0.4, 0.25 ≤ y ≤ 0.4, and 0.35 ≤ z ≤ 0.4) ternary ceramics with different compositions were synthesized and it was found that the strain response was not sensitive to the composition. The crystal structure, strain response, ferroelectric properties, and temperature stability of x BMT– y PZ– z PT ceramics were investigated in detail. X‐ray diffraction patterns show that all the as‐prepared x BMT– y PZ– z PT ceramics with x = 0.2, 0.3, 0.4, and 0.5 possess a perovskite structure. Under an external electric field of 6 kV mm ⁻¹ , the strain values of x BMT– y PZ– z PT ternary ceramics with x = 0.2, 0.3, 0.4, and 0.5 were 0.30%, 0.31%, 0.30%, and 0.27%, respectively. In addition, the strain hysteresis of these ternary ceramics is also almost the same and low. These merits make x BMT– y PZ– z PT piezoelectric ceramics have broad application prospects in the field of commercial actuators.
To explore new lead-free piezoelectric materials that is both environmentally friendly and healthy to provide the possibility for material selection for microelectromechanical systems. Lead-free piezoelectric (1-x)(0.8Bi0.5Na0.5TiO3-0.2Bi0.5K0.5TiO3)-xBi(Ni0.5Zr0.5)O3 thin films (abbreviated as BNT-BKT-xBNZ) (x=0.00, 0.01, 0.02, 0.03, 0.04) were prepared on Pt(111)/Ti/SiO2/Si substrates by a sol-gel method. Impacts of Bi(Ni0.5Zr0.5)O3 content on the microstructure, dielectric, ferroelectric, and piezoelectric properties were also investigated detailedly. It found that the Bi(Ni0.5Zr0.5)O3 composition had a great influence on the increase of relaxor and the decrease of the oxygen vacancies, which is influential to the promotion of thin-film properties. Thin-film of BNT-BKT-0.02BNZ showed the optimum electrical properties with the polarization of 40.27 μC/cm², dielectric constants of 477 and effective inverse piezoelectric coefficient reach up to 125.9 p.m./V. Results revealed that the BNT-BKT thin films with 0.02 mol% Bi(Ni0.5Zr0.5)O3-doped are a kind of lead-free piezoelectric materials with superior manifestations with a great development prospect for applications.
The control of grain orientation by introducing Nb-doped SrTiO3 single crystalline substrates is an effective way to improve piezoelectric and ferroelectric properties of thin films. Therefore, in this work, 0.99(0.94Bi0.5Na0.5TiO3–0.06BaTiO3)–0.01BiMnO3 thin films were coated on Pt(111)/TiOx/SiO2/Si(001) polycrystalline substrates and Nb-doped SrTiO3 single crystalline substrates, respectively. The Nb-doped SrTiO3 single crystalline substrates can affect the orientation of the BNT–BT–0.01BMO thin films, promote the grain growth, reduce the leakage current, and form an interfacial layer between the thin film and the substrate, and a comparatively larger converse piezoelectric coefficient (46.49 pm·V⁻¹), a high energy storage density (56.5 J·cm⁻³), and a high energy storage efficiency (79.4%) were therefore simultaneously achieved in the thin films grown on Nb-doped SrTiO3 single crystalline substrates, promising the oriented thin films broad application prospects.
In this work, structures, photo-absorption, characteristics, and electrical properties of Al-doped BiFeO3 were experimentally investigated in powder and in bulk states. BiFe1-mAlmO3 (m = 0, 2%, 4%, 6% and 8%) powders and ceramics were synthesized by sol-gel method followed by two-step sintering to yield products, which were denoted as A-0, A-2, A-4, A-6, and A-8, respectively. X-ray diffraction (XRD) showed that Al-doped powders and ceramics maintained their rhombic perovskite structures. Scanning electron microscopy (SEM) results confirmed that average grain size of as-prepared ceramics were preserved below micron-level because of the two-step sintering process. By comparison, grain size of Al-doped ceramics were maintained at about 0.6 μm. Optical bandgaps of powders estimated from UV–vis absorbance spectroscopy and Tauc relationship illustrated values that varied from 1.85 eV to 2.05 eV becaused of the Moss-Burstein effect. Leakage current densities declined by 2–3 orders of magnitude, indicating significantly increased resistivity due to Al-doping cause liquid phase segregation. Dielectric and ferroelectric properties also improved. However, dielectric loss decreased and breakdown voltage increased. The resistivity, coercive field (2Ec), and residual polarization intensity (2Pr and ΔP) of A-4 ceramic were recorded as 3.71 × 10⁶ Ω m, 43.7 kV/cm, 1.93 and 1.28 μC/cm², respectively. In sum, modified BFO appears to be a promising new way to fabricate intensive devices.
BiMeO3 (where Me denotes a transition metal) is often used as a chemical modifier to form the Bi0.5Na0.5TiO3‐based solid solutions and to improve the electromechanical properties of the materials. In this work, BiMnO3 was selected as a chemical modifier, and (1‐x)(0.94Bi0.5Na0.5TiO3–0.06BaTiO3)–xBiMnO3 thin films with x = 0, 0.005, 0.01 and 0.015 were fabricated using the metal organic decomposition method to study the contributions of the third end member BiMnO3 to the reduction of the leakage current and the enhancement of the piezoelectric properties of Bi0.5Na0.5TiO3–BaTiO3 thin films. Thin films with 1 mol% BiMnO3 exhibit a lower leakage current, and a better piezoelectricity and ferroelectricity, whose Smax/Emax, Pmax, 2Ec and εr are 100.4 pm/V, 48.0 μC/cm2, 54.9 kV/cm and 942, respectively.
Lead free Bi0.5(Na0.8K0.2)0.5TiO3 thin films doped with BiFeO3 (abbreviated as BNKT-xBFO) (x = 0, 0.02, 0.04, 0.08, 0.10) were deposited on Pt(111)/Ti/SiO2/Si substrates by sol-gel/spin coating technique and the effects of BiFeO3 content on the crystal structure and electrical properties were investigated in detail. The results showed that all the BNKT-xBFO thin films exhibited a single perovskite phase structure and high-dense surface. Reduced leakage current density, enhanced dielectric and ferroelectric properties were achieved at the optimal composition of BNKT-0.10BFO thin films, with a leakage current density, dielectric constant, dielectric loss and maximum polarization of <2×10⁻⁴ A/cm³, ~978, ~0.028 and ~74.13 μC/cm² at room temperature, respectively. Moreover, the BNKT-0.10BFO thin films possessed superior energy storage properties due to their slim P-E loops and large maximum polarization, with an energy storage density of 22.12 J/cm³ and an energy conversion efficiency of 60.85% under a relatively low electric field of 1200 kV/cm. Furthermore, the first half period of the BNKT-0.10BFO thin film capacitor was about 0.15 μs, during which most charges and energy were released. The large recoverable energy density and the fast discharge process indicated the potential application of the BNKT-0.10BFO thin films in electrostatic capacitors and embedded devices.
New ternary lead free CaSnO3-CaTiO3-NaNbO3 (CSNNTx) ferroelectrics were prepared by a solid-state reaction method. The X-ray diffraction patterns at room temperature revealed a single phase perovskite crystallizing with cubic Pm3m group symmetry for x<0.8 and in tetragonal group P4mm for x≥0.8. The real part of the relative dielectric permittivity (ε'r) exhibited a sharp peak with no frequency dependence which revealed a classical ferroelectric behavior for some compositions and ferroelectric relaxor behavior for others, with a diffuse phase transition and frequency dispersion. The ferroelectric behavior has been confirmed by hysteresis investigation. Raman spectra at room temperature shows a disorder introduced in this composition, thus favoring a ferroelectric relaxor behavior.
New lead-free perovskite solid solution ceramics of (1 − x)(Bi1/2Na1/2)TiO3–xBa(Ni1/2Nb1/2)O3[(1−x)BNT–xBNN,x = 0.02–0.06) were prepared and their dielectric, ferroelectric, piezoelectric, and electromechanical properties were investigated as a function of the BNN content. The X-ray diffraction results indicated that the addition of BNN has induced a morphotropic phase transformation from rhombohedral to pseudocubic symmetry approximately at x = 0.045, accompanying an evolution of dielectric relaxor behavior as characterized by enhanced dielectric diffuseness and frequency dispersion. In the proximity of the ferroelectric rhombohedral and pseudocubic phase coexistence zone, the x = 0.045 ceramics exhibited optimal piezoelectric and electromechanical coupling properties of d33~121 pC/N and kp~0.27 owing to decreased energy barriers for polarization switching. However, further addition of BNN could cause a decrease in freezing temperatures of polar nanoregions till the coexistence of nonergodic and ergodic relaxor phases occurred near room temperature, especially for the x = 0.05 sample which has negligible negative strains and thus show the maximum electrostrain of 0.3% under an external electric field of 7 kV/mm, but almost vanished piezoelectric properties. This was attributed to the fact that the induced long-range ferroelectric order could reversibly switch back to its original ergodic state upon removal of external electric fields.
The effects of CaZrO3 substitution on the crystal structure, electric field–induced strain, and piezoelectric properties of Bi0.5(Na0.78K0.22)0.5TiO3 ceramics have been investigated. The CaZrO3 substitution resulted in a transition from ferroelectric tetragonal to pseudocubic symmetry with relaxor characteristics, leading to degradations in the piezoelectric coupling coefficient, electromechanical quality factor, and piezoelectric coefficient d 33. However, the electric field–induced strain was significantly enhanced by the CaZrO3-induced phase transition and reached a highest value of S max/E max = 617 pm/V when CaZrO3 content reached 3 mol%. The result supports a prediction that a large strain at the ferroelectric–relaxor transition region can be observed when the tolerance factor of the Bi-perovskite is decreased by the substitution of ABO3-type modifiers.
Bi(Mg1/2Ti1/2)O3-PbTiO3 is a promising high-TC piezoelectrics in the Bi-based perovskite family of BiMeO3-PbTiO3. In this study, zirconium is utilized to further improve the high temperature piezoelectric properties of Bi(Mg1/2Ti1/2)O3-PbTiO3. Substitution of Zr for Ti is observed to decrease the tetragonality (c/a) near the morphotropic phase boundary, while TC can be well maintained by the substitution of smaller and ferroelectrically active Ti by a larger and ferroelectrically weaker Zr cation. A softer coercive field and enhanced domain mobility is observed, ultimately leading to a strong ferroelectric activity. The piezoelectric property of Zr-substituted Bi(Mg1/2Ti1/2)O3-PbTiO3 is enhanced to 260 pC/N, when compared with Bi(Mg1/2Ti1/2)O3-PbTiO3 (225 pC/N). Good high temperature piezoelectric property was found in the tetragonal phase of Zr-substituted Bi(Mg1/2Ti1/2)O3-PbTiO3. Thermal depoling of aligned domains for this composition occurs at approximately 300 °C. Thus, Zr-substituted Bi(Mg1/2Ti1/2)O3-PbTiO3 could be used for high temperature actuator applications. Furthermore, an apparent ferroelectric-antiferroelectric phase transition was observed as a function of both the composition in the rhombohedral phase and the temperature. An antiferroelectric relaxor exists in the Zr-substituted Bi(Mg1/2Ti1/2)O3-PbTiO3.
In 0.95[0.94Bi0.5Na0.5TiO3-0.06BaTiO3]-0.05CaTiO3 ceramics, the temperature TS (dielectric
permittivity shoulder at about 125 �C) represents a transition between two different thermally
activated dielectric relaxation processes. Below TS, the approximately linear decrease of the
permittivity with the logarithm of frequency was attributed to the presence of a dominant ferroelectric
phase. Above TS, the permittivity shows a more complicated dependence of the frequency and Raman
modes indicate a sudden increase in the spatial disorder of the material, which is ascribed to the
presence of a nonpolar phase and to a loss of interaction between polar regions. From 30 to 150 �C, an
increase in the maximum polarization with increasing temperature was related to three possible
mechanisms: polarization extension favoured by the simultaneous presence of polar and non-polar
phases; the occurrence of electric field-induced transitions from weakly polar relaxor to ferroelectric
polar phase; and the enhanced polarizability of the crystal structure induced by the weakening of the
Bi-O bond with increasing temperature. The occurrence of different electric field induced polarization
processes with increasing temperature is supported by the presence of additional current peaks in the
current-electric field loops.
Relaxor ferroelectrics are materials exhibiting dielectric dispersions in their maximum permittivity temperature without macroscopic phase transition into a ferroelectric state. Their exceptional properties are exploited in a variety of dielectric and piezoelectric applications. As it is generally believed that polar nanoregions play a crucial role in relaxor behavior, there are great interests in exploring how the atomic structures affect the relaxor properties. Here, using the dark field imaging and atomic-resolution electron microscopy, we investigate the nano and atomic structure of a lead-free ferroelectric-relaxor Ba(Ti1−xSnx)O3 system at high temperature. The local atom displacements and their spatial correlations are measured, and the atomic structure of static polar nanoregions in the relaxors is reported. For the materials exhibiting normal ferroelectricity, no such static polar structures can be seen. Based on our experimental observations, we suggest the static polar nanoregions are responsible for the relaxor behavior in this lead-free system.
Transition lines between various phases in the electric-field-temperature phase diagram of 9/65/35 lanthanum-modified lead zirconate titanate ceramics were determined by measurements of the temperature and electric-field-dependent dielectric constant. Above a critical field (E-C) the dc bias electric field induces a transition from the relaxer (R) to the long-range ferroelectric (FE) phase. In the temperature direction of the approach to the FE phase the R-FE; transition line was determined from the field-cooled-field-heated dielectric susceptibilities, while depolarization temperatures were obtained from the field-cooled-zero-field-heated dielectric susceptibilities. A considerably large shift was found for the above two R-FE transition lines demonstrating the strong impact of the electric field on the stability of the FE phase with increasing temperature. It was found that below E-C ergodicity is broken due to the divergence of the longest relaxation time at the freezing temperature T-0 = 259 K. Hence the system exhibits a transition line between the ergodic (ER) and nonergodic (NR) relaxor state. In the de bias field direction of the approach to the FE phase, the temperature dependence of E-C, i.e., the transition lines between ER or NR and FE phases were studied by measurements of the complex dielectric constant as a function of a de bias field at several fixed temperatures. The experimental results are compared with the results of a spherical random bond-random field model of relaxer ferroelectrics.
The mechanism of the giant unipolar strain recently observed in a lead-free piezoceramic, 0.92( Bi <sub>0.5</sub> Na <sub>0.5</sub>) TiO <sub>3</sub>-0.06 BaTiO <sub>3</sub>-0.02( K <sub>0.5</sub> Na <sub>0.5</sub>) NbO <sub>3</sub> [S.-T. Zhang, A. B. Kounga, E. Aulbach, H. Ehrenberg, and J. Rödel, Appl. Phys. Lett. 91, 112906 (2007) was investigated. The validity of the previously proposed mechanism that the high strain comes both from a significant volume change during the field-induced phase transition, from an antiferroelectric to a ferroelectric phase and the domain contribution from the induced ferroelectric phase was examined. Monitoring the volume changes from the simultaneously measured longitudinal and transverse strains on disk-shaped samples showed that the phase transition in this specific material does not involve any notable volume change, which indicates that there is little contribution from a volume change due to the phase transition to the total strain response. Temperature dependent hysteresis measurements on unpoled samples of a nearby ferroelectric composition, 0.93( Bi <sub>0.5</sub> Na <sub>0.5</sub>) TiO <sub>3</sub>-0.06 BaTiO <sub>3</sub>-0.01( K <sub>0.5</sub> Na <sub>0.5</sub>) NbO <sub>3</sub> demonstrated that the origin of the large strain is due to the presence of a nonpolar phase that brings the system back to its unpoled state once the applied electric field is removed, which leads to a large unipolar strain.
The effective ionic radii of Shannon & Prewitt [Acta Cryst. (1969), B25, 925-945] are revised to include more unusual oxidation states and coordinations. Revisions are based on new structural data, empirical bond strength-bond length relationships, and plots of (1) radii vs volume, (2) radii vs coordination number, and (3) radii vs oxidation state. Factors which affect radii additivity are polyhedral distortion, partial occupancy of cation sites, covalence, and metallic character. Mean Nb5+-O and Mo6+-O octahedral distances are linearly dependent on distortion. A decrease in cation occupancy increases mean Li+-O, Na+-O, and Ag+-O distances in a predictable manner. Covalence strongly shortens Fe2+-X, Co2+-X, Ni2+-X, Mn2+-X, Cu+-X, Ag+-X, and M-H- bonds as the electronegativity of X or M decreases. Smaller effects are seen for Zn2+-X, Cd2+-X, In2+-X, pb2+-X, and TI+-X. Bonds with delocalized electrons and therefore metallic character, e.g. Sm-S, V-S, and Re-O, are significantly shorter than similar bonds with localized electrons.
The diffuseness of the ferroelectric phase transition in PbMg1/3Nb2/3O3 is proposed to be due to quenched random electric fields originating from charged compositional fluctuations. They are responsible for the extreme critical slowing down, the freezing into nanometric ferroelectric domains, and the slow relaxation of the polarization below Tc~212 K. Barkhausen jumps during poling exclude glassiness, which was conjectured previously. At Tc a ferroelectric anomaly of the dielectric permittivity appears, if the random fields are overcome by an external electric field.
The temperature dependence of the dielectric nonlinearities in a PMN single crystal and in 9/65/35 PLZT ceramics has been determined by measuring the first and third harmonic response as well as the dielectric behavior as a function of the dc electric field. In zero field a paraelectric-to-glass, and, in a high enough dc field, a glass-to-ferroelectriclike crossover in the temperature dependence of the nonlinear response have been observed. Both crossovers agree with the predictions of the spherical random-bond-random-field model. Relaxors thus undergo in zero field a transition to a spherical glass, while above the critical field a transition into a ferroelectric state occurs.
The effects of co-doping with Ta- and Li-ions on the microstructure, crystal structure, ferroelectric, and electric field-induced strain properties of Bi1/2(Na0.82K0.18)1/2TiO3 (BNKT) ceramics were investigated. Li substitution into Na-sites led to a ferroelectric-nonpolar phase transition and a large accompanying normalized strain (Smax/Emax) of 727 pm/V near the phase boundary, when 2.5 mol% Li and 2.5 mol% Ta were co-doped on A- and B-sites, respectively. The phase transition-related strain was thought to be induced by a decrease in the tolerance factor of the perovskite structure.
The structure and electric properties of (0.9-x)Bi(Mg1/2Ti1/2)O3-xPbTiO3-0.1BaZrO3 (0.45 ≤ x ≤ 0.53) ceramics were investigated. The morphotropic phase boundary between tetragonal ferroelectric and pseudo-cubic relaxor phases is ascertained at x = 0.50. The BaZrO3 substitution can much reduce the coercive field of Bi(Mg1/2Ti1/2)O3-PbTiO3. The studies on temperature dependence of both ferroelectric and dielectric constant indicate a direct evidence for the antiferroelectric relaxor phase, which was ever suggested in the binary system of Bi(Mg1/2Ti1/2)O3-PbTiO3. The phase transition of ferroelectric to antiferroelectric relaxor produces the thermal depoling below the Curie temperature. The ceramic of BMT-0.47PT-0.1BZ exhibits a high strain 0.37% and a large-signal d33 (530 pm/V) in the antiferroelectric-relaxor phase. BaZrO3 substituted Bi(Mg1/2Ti1/2)O3-PbTiO3 shows an analogous phase diagram to that of lead-free (Bi, Na)TiO3-BaTiO3.
BiFeO3-PbTiO3 (BF-PT) compounds possess very high Curie temperature and tetragonality compared to other PbTiO3-based piezoceramics. The BaZrO3 (BZ), with weakly ferroelectric active cations, was introduced into the BiFeO3-PbTiO3 to reduce the tetragonality (c/a) and improve the piezoelectric property. For the (0.8-x)BiFeO3-0.2BaZrO3-xPbTiO3, the BaZrO3 substitution can effectively decrease the tetragonality (c/a) from 1.18 to 1.02 for those compositions near the morphotropic phase boundary. The piezoelectric property of BiFeO3-PbTiO3 can be much enhanced with an optimal piezoelectric constant ∼270 pC/N with a reduced TC of 270 °C. Both the temperature dependent dielectric properties and polarization loops verified the existence of antiferroelectric relaxor, which was not observed in previous reported BiFeO3-PbTiO3 based materials.
Extremely enhanced electrostrains (up to 0.39%) were surprisingly observed in (0.67 − x)Bi(Mg0.5Ti0.5)O3–xPbZrO3–0.33PbTiO3 (BMT–xPZ–PT) ternary solid solutions, possibly resulting in BMT–xPZ–PT ceramics having great potential for large-displacement actuator applications. The generation of giant strains was found to be closely associated with the evolution of a weak relaxor behavior from diffuse-type BMT–PT binary ferroelectrics, during which the domain switching is actively facilitated owing to a change in the dynamics of the polar nanoregions from a static state to a dynamic state. It can be also attributed to a ferroelectric nature of the evolved relaxors in PZ substituted BMT–PT ceramics instead of a dipole glass freezing state. These judgements were reasonably supported by a couple of measurements, including strains vs. electric field, Raman scattering, dielectric spectroscopy and the time- and electric-field-dependent polarization. The present study can provide a general approach towards an appropriate compositional design for large electrostrains in BMT-based and related systems.
(1−x)(Bi0.5K0.5)TiO3–xLiNbO3 ((1−x)BKT–xLN) lead-free relaxor ferroelectric ceramics were prepared by a conventional solid-state route and their phase transition behavior and the corresponding electrical properties were investigated. A morphotropic phase boundary separating rhombohedral and tetragonal phases was identified in the composition range of 0.015<x<0.03, where the improved electrical properties of piezoelectric constant d33=75 pC/N and electromechanical coupling factor kp=0.18 were obtained. Moreover, all samples show typical relaxor behavior characterized by the presence of diffuse phase transition and frequency dispersion. It was found that the dielectric relaxation behavior of BKT ceramics can be obviously enhanced with the addition of LN. In addition, the effect of the LN addition on the ferroelectric properties was also investigated by measuring polarization versus electric field hysteresis loops.
The electromechanical properties of (Pb1−xLax)(ZryTi1−y)O3 [PLZT x/y/(1 - y)] have been investigated in the compositional range 0 < x < 0.10 for y = 0.65 (rhombohedral PLZT) and 0 < x < 0.18 for y = 0.40 (tetragonal PLZT). Both field-induced strains (∊-E) associated with polarization switching and piezoelectric responses (d33) were studied. Transmission electron microscopy (TEM) and dielectric investigations were also performed. Room temperature TEM investigations revealed common trends in the domain structure with increasing La content for both PLZT x/65/35 and x/40/60, including a micron-sized domain structure, a subdomain tweed-like structure, and a nanopolar domain state. Changes in the field-induced strains and piezoelectric properties were then related to these microstructural trends. The dominant electromechanical coupling mechanism in the micron-sized domain state was found to be piezoelectricity. However, an electrostrictive coupling became apparent with the appearance of the subdomain tweed-like structures, and became stronger in the nanopolar domain state. It is believed that polarization switching can-occur through 70°or 110°domains, the subdomain tweed-like structure, or nanopolar domains depending on La content.
This letter presents direct electron diffraction evidence that structurally frustrated one-dimensional polar nanoregions arising from anticorrelated displacements of Ti and nearest neighboring O ions are responsible for the relaxation behavior observed in doped BaTiO3 relaxor ferroelectrics, rather than chemical short range ordering. The role of the dopant ions is not to directly induce polar nanoregions but rather to set up random local strain fields preventing homogeneous strain distortion, thereby suppressing transverse correlation from one ⟨001⟩ chain dipole to the next and hence the development of long range ferroelectric order.
The effect of Sr vacancies on the behavior of strontium titanate with trivalent dopants (La3+, Gd3+, and Y3+) substituting Sr2+ ions is reported. A remarkable shift of the antiferrodistortive transition temperature T-a is revealed by Raman spectroscopy for just a small content of dopant. It is shown that a unique linear dependence of Ta versus tolerance factor is obtained when Sr-vacancies are taken into account. A vacancy size value of similar to 1.54 angstrom is estimated, which is similar to 7% larger than Sr2+ radius. This size difference enables explaining the unexpected increase of lattice parameter with increasing Bi3+ content in Sr1-1.5xBixTiO3.
Feature size is a natural determinant of material properties. Its design offers the technological perspectives for material improvement. Grain size, crystallite size, domain width, and structural defects of different nature constitute the classical design elements. Common ferroelectric ceramics contain micrometer grain sizes and submicrometer domain widths. Domain wall mobility is a major contribution to their macroscopic material properties providing approximately half of the macroscopic output in optimized materials. The extension into the dynamic nanoworld is provided by relaxor ferroelectrics. Ionic and nanoscale field disorders form the base to a state with natural nanometer-size polar structures even in bulk materials. These polar structures are highly mobile and can dynamically change over several orders of magnitude in time and space being extremely sensitive to external stimuli. This yields among the largest dielectric and piezoelectric constants known. In this feature article, we want to outline how lead-free relaxors will offer a route to an environmentally safer option in this outstanding material class. Properties of uniaxial, planar, and volumetric relaxor compositions will be discussed. They provide a broader and more interesting scope of physical properties and features than the classical lead-containing relaxor compositions.
Electric-field-forced antiferroelectric-to-ferroelectric phase transitions in several compositions of modified lead zirconate titanate stannate antiferroelectric ceramics are studied for ultra-high-field-induced strain actuator applications. A maximum field-induced longitudinal strain of 0.85% and volume expansion of 0.95% are observed in the ceramic composition Pb0.97La0.02(Zr0.66Ti0.09Sn0.25)O3 at room temperature. Switching from the antiferroelectric form to the ferroelectric form is controlled by the nucleation of the ferroelectric phase from the antiferroelectric phase. A switching time of <1 μs is observed under the applied field above 30 kV/cm. The polarization and strains associated with the field-forced phase transition decrease with increasing switching cycle, a so-called fatigue effect. Two types of fatigue effects are observed in these ceramic compositions. In one, the fatigue effects only proceed to a limited extent and the properties may be restored by annealing above the Curie temperature, while in the other, the fatigue effects proceed to a large extent and the properties cannot be restored completely by heat treatment. Hydrostatic pressure increases the transition field and the switching time. But when the applied electric field is larger than the transition field, the induced polarization and strain are not sensitive to increasing hydrostatic pressure until the transition field approaches the applied field.
The purpose of this work was to evaluate the effect of compositional modifications on the electrical properties of lead lanthanum zirconate stannate titanate (PLZST) ceramics, as well as to examine their electrically induced phasechange behavior. Variations in the Ti:Sn ratio were evaluated. Increased Ti4+ content produced the following: decreased switching field, related to an increased antiferro-electric-ferroelectric (AFE-FE) transition temperature; constant hysteresis (ΔE) correlated with a constant temperature of the maximum dielectric constant (Tmax); a sharper dielectric-constant maximum peak; and increased room-temperature dielectric constant (K). Variations in the Zr:Sn ratio also were evaluated. Increased Zr4+ content produced the following: increased hysteresis with increased Tmax, decreased maximum dielectric constant, and decreased switching field with increased AFE-FE transition temperature (TAFE_FE). From these results, with respect to compositional modifications, the AFE-FE switching field (EAFE_FE) and ΔE were observed to be dependent strongly on TAFE_FE and Tmax, respectively. Negligible change existed in the strain achievable at the switching field, which remained constant for all compositions at ∼0.16%. The significance of this research was the ability demonstrated to tailor the properties of phase-change materials through compositional modifications.
Recently, it has been shown that, upon cooling, disordered Pb(Sc 1/2 Ta 1/2 )O 3 ceramics transform spontaneously from a relaxor state to a ferroelectric state when processed in a manner that suppresses lead vacancies. If lead vacancies are present, the spontaneous ferroelectric transition is suppressed and the ceramics exhibit the usual relaxor behavior in a wide temperature range. It is shown that disordered Pb(Sc 1/2 Nb 1/2 )O 3 ceramics have a similar nature: When produced in a manner that does not eliminate lead vacancies, they exhibit normal relaxor behavior. However, if stoichiometry is tightly controlled, disordered Pb(Sc 1/2 Nb 1/2 )O 3 transforms spontaneously (under zero‐bias field) from a relaxor into a normal ferroelectric upon cooling. © 1995 American Institute of Physics.
(1-x) Bi(Mg <sub>1/2</sub> Ti <sub>1/2</sub>) O <sub>3</sub>–x PbTiO <sub>3</sub> polycrystalline ceramics were investigated for potential as high-temperature piezoelectric materials. A morphotropic phase boundary (MPB) between tetragonal (T) and rhombohedral (R) ferroelectric (FE) phases, which exhibited enhanced piezoelectric activity and a ferroelectric–paraelectric phase transition at 478 °C was observed at x≈0.37. Electron diffraction patterns (x≤0.37) contained discrete superlattice reflections at 1 2 {hkl} positions arising from antiphase rotations of the O octahedra, consistent with R3c space group symmetry. These reflections were diffuse at the MPB (x=0.38) and absent in the T phase (x=0.5). In the unpoled state, FE R (x=0.35) ceramics revealed a polar microdomain structure whereas the T phase (x=0.5) contained classic {110} twin domain boundaries. However, poled R samples underwent a field-induced transformation to an aligned domain structure with {110} twin boundaries similar to those in the T phase. Correlations are made between structure and properties for these piezoelectric materials. © 2004 American Institute of Physics.
This paper explores the special characteristics of ferroelectric materials which make them highly suitable for application as both sensors and actuators in electromechanical (smart) systems. The domain structure which gives the possibility to impart a polar axis in a randomly axed polycrystal ceramic is essential for piezoelectricity, but all electromechanical behavior may be traced ultimately to the electrostrictive coupling between polarization and strain fields. Topics to be discussed will include: (1) the special advantages of materials in the lead zirconate:lead titanate solid solution systems for both sensing and actuation; (2) domain and phase switching contributions to electrical, mechanical and coupled responses; (3) scaling effects in ferroics and the origins of the relaxor ferroelectric behavior of electrostrictive ceramics; (4) composite polymer:ceramic systems and the maneuverability engendered by phase connectivity control.
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