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Bi2Te3-PLZT(9/65/35)-PVDF multifunctional nanocomposite films for futuristic energy harvestors
Abstract
This article highlights the influence of ternary material combination of thermoelectric 0.5Bi2Te3 (BT), ferroelectric 0.5(PLZT9/65/35) (PLZT) nanopowders dispersed in polymer PVDF matrix to form a 0.5Bi2Te3-0.5[Pb0.91La0.09(Zr0.65Ti0.35)0.9775O3]-PVDF nanocomposite thin film. BT and PLZT were prepared by using simple precipitation method to form 0.5BT-0.5PLZT-PVDF nanocomposite thin film. As heat treated BT and PLZT were characterized for phase analysis by powder X-ray diffraction, and microstructure studies by scanning electron microscopy and transmission electron microscopy. Nanocomposite thin films were characterized for room temperature dielectric, thermoelectric and ferroelectric studies. XRD patterns attested clear crystalline mixture of Bi2Te3 trigonal showing rhombohedral structure and perovskite PLZT showing ternary FERH, FETET, and FECUBIC structures at the morphotrophic phase boundary. SEM with EDS and TEM results of thermoelectric Bi2Te3, ferroelectric (PLZT:9/65/35) and 0.5Bi2Te3-0.5[Pb0.91La0.09(Zr0.65Ti0.35)0.9775O3] are reported. The nanoparticles of this system ranged between 17 nm and 82 nm. Dielectric, thermoelectric and ferroelectric results of the 0.5Bi2Te3-0.5[Pb0.91La0.09(Zr0.65Ti0.35)0.9775O3]-PVDF nanocomposite thin film was discussed. The remanent and spontaneous polarization and coercive field of BT-PLZT-PVDF film are observed as 2.52 µC/cm², 3.28 µC/cm and 196.63 kV/cm, respectively that could be interesting candidate for possible futuristic energy harvesting, biomedical and smart applications.
This work proposes an enhanced method for thermal energy harvesting
exploiting combined pyroelectric, piezoelectric and shape memory (SME)
effects, and presents its experimental validation. A material which is
pyroelectric is also piezoelectric. If it is combined with a material
with SME, which generates large strain and stress in a rather narrow
temperature range, the resulting composite material would generate
voltage from temperature variations using two different energy
conversion principles at once: (1) pyroelectric effect, (2)
piezoelectric effect driven by SME. A Macro Fiber Composite
piezoelectric was shown here to exhibit significant pyroelectric effect
(~4 V/°C). When combining it with a SME Ti-Ni-Cu alloy into a
laminated structure, this effect increased by 50%. This increase may be
an order of magnitude higher for an optimized system. Such composites
open an opportunity to harvest thermal energy from natural sources,
since this method can increase the rather low efficiency of current
pyroelectric materials especially for small temperature variations.
Topological insulators are new states of quantum matter in which surface states residing in the bulk insulating gap of such systems are protected by time-reversal symmetry. The study of such states was originally inspired by the robustness to scattering of conducting edge states in quantum Hall systems. Recently, such analogies have resulted in the discovery of topologically protected states in two-dimensional and three-dimensional band insulators with large spin–orbit coupling. So far, the only known three-dimensional topological insulator is BixSb1-x, which is an alloy with complex surface states. Here, we present the results of first-principles electronic structure calculations of the layered, stoichiometric crystals Sb2Te3, Sb2Se3, Bi2Te3 and Bi2Se3. Our calculations predict that Sb2Te3, Bi2Te3 and Bi2Se3 are topological insulators, whereas Sb2Se3 is not. These topological insulators have robust and simple surface states consisting of a single Dirac cone at the point. In addition, we predict that Bi2Se3 has a topologically non-trivial energy gap of 0.3 eV, which is larger than the energy scale of room temperature. We further present a simple and unified continuum model that captures the salient topological features of this class of materials.
We report a novel synthesis for near monodisperse, sub-10-nm Bi2Te3
nanoparticles. At first, a new reduction route to bismuth nanoparticles is
described which are applied as starting materials in the formation of
rhombohedral Bi2Te3 nanoparticles. After ligand removal by a novel hydrazine
hydrate etching procedure, the nanoparticle powder is spark plasma sintered to
a pellet with preserved crystal grain sizes. Unlike previous works on the
properties of Bi2Te3 nanoparticles, the full thermoelectric characterization of
such sintered pellets shows a highly reduced thermal conductivity and the same
electric conductivity as bulk n-type Bi2Te3.
Based on the optical characteristics of PLZT electro-optic ceramic, two kinds of electro-optic deflectors, triangular electrode structure and optical phased array technology, are studied in detail by using transverse electro-optic effect. Theoretically, the electro-optic deflection characteristics and mechanisms of the deflectors are analyzed. Experimentally, the optical characteristics of ceramic wafer, such as the phase modulation, the hysteresis and the electro-induced loss characteristics, are measured firstly, and then the beam deflection experiments are designed to verify the theoretical results. Moreover, the effect of temperature on the performance of triangular electrode deflector is investigated. The characteristics of both deflectors are also compared and illuminated.
Type-I edge-localized modes (ELMs) have been mitigated at the JET tokamak using a static external n=1 perturbation field generated by four error field correction coils located far from the plasma. During the application of the n=1 field the ELM frequency increased by a factor of 4 and the amplitude of the D(alpha) signal decreased. The energy loss per ELM normalized to the total stored energy, DeltaW/W, dropped to values below 2%. Transport analyses shows no or only a moderate (up to 20%) degradation of energy confinement time during the ELM mitigation phase.
PLZT thin-film channel waveguides have been successfully formed in ridges by an ion-beam etching process. The electrooptic Kerr coefficients of the waveguides have been newly obtained. We have determined that the electrooptic coefficients R 11 ′ and R 12 ′ were 0.1–0.2 × 10⁻¹⁶ (m/V)² and 0.01 × 10⁻¹⁶ (m/V)², respectively, by Mach-Zehnder interferometric measurement. It was confirmed that PLZT channel waveguides were much more efficient than conventional Ti-diffused LiNbO3 waveguides.
The topological invariants of a time-reversal-invariant band structure in two
dimensions are multiple copies of the invariant found by Kane
and Mele. Such invariants protect the topological insulator and give rise to a
spin Hall effect carried by edge states. Each pair of bands related by time
reversal is described by a single invariant, up to one less than
half the dimension of the Bloch Hamiltonians. In three dimensions, there are
four such invariants per band. The invariants of a crystal
determine the transitions between ordinary and topological insulators as its
bands are occupied by electrons. We derive these invariants using maps from the
Brillouin zone to the space of Bloch Hamiltonians and clarify the connections
between invariants, the integer invariants that underlie the
integer quantum Hall effect, and previous invariants of -invariant
Fermi systems.
This paper summarises the information obtained here in the Solid State Physics Laboratory during a programme of research on bismuth telluride. Earlier papers [1–3] have discussed some of its properties with reference to applications of the Seebeck and Peltier effects.
Nanostructured graphene/Bi2Te3 composites were fabricated with either Bi2Te3 powder or nanowires (NWs) and various graphene contents, and their thermoelectric properties were investigated. The Bi2Te3 powder was produced from Bi2Te3 beads with a conventional ball milling process, whereas the Bi2Te3 NWs were fabricated with a solution-phase synthetic route. The composites with a graphene content of 0.5 wt.% exhibited enhanced power factors, presumably because of an improvement in the Seebeck coefficients of the samples, which overwhelmed the reduction in electrical conductivity. In addition, the introduction of graphene reduced the lattice thermal conductivity of the composites because it caused the formation of many boundaries in the Bi2Te3 matrix. The maximum thermoelectric figure of merit (ZT) of 0.4 was achieved at 300 K with the 1 wt.%-graphene/Bi2Te3-NW composite; it was larger than that of the pristine Bi2Te3 NWs and graphene/Bi2Te3-powder composites.
This review of the PLZT materials and their applications describes the present state of the technology and emphasizes the latest developments in the field of electrooptic ceramics. Despite the reported development of new, transparent materials in other compositional systems, the PLZT's still remain the standard of the industry and continue to find an ever increasing number of applications in the areas of shutters, filters, displays, and spatial light modulators. Their fast response, high resolution and wide operating temperature range make them viable candidates for several emerging technologies including high resolution, non-impact, facsimile printing, electrophotographic copying, color reproduction and integrated optical processing. With the presently successful development of sputtered PLZT thin films, both bulk and thin film PLZT materials can now be considered for future electrooptic devices.
Crystal growth conditions of Bi2Te3 narrow bandgap semiconductors have been studied using molecular beam epitaxy method. It was applied to the growth of Bi2Te3 on Bridgman single-crystal substrate Sb2Te3. Substrate ingots were taken from the natural cleavage along the (0001) plane. The deposited conditions have been studied as a function of substrate temperature (Ts) and flux ratio (. The quality of deposited layers was controlled by X-ray diffraction, scanning electron microscope (SEM), secondary ion mass spectroscopy (SIMS) depth profiling and energy-dispersive X-ray (EDX) microanalyser. The sticking coefficients Ks(Te) and Ks(Bi) of the elements that compose Bi2Te3 were determined. It was found that the stoichiometry of deposited layers depended on substrate temperature and flux ratio. It was observed that all deposited layers were single-crystal in the orientation of their substrates with a small shift due to the stress in layer.
Bismuth telluride material was fabricated using ultrarapid quenching process route, which is unusual to get polycrystalline materials for thermoelectric applications. The microstructural study showed that the obtained microstructures are very different from those obtained by normal cooling, which should induce new physical properties. The ultrarapid quenched material was obtained in the shape of foils, the thickness of which was found to vary in the range of 10–60μm, which corresponds to a cooling rate of about 106K/s. Scanning electron microscopy associated with energy-dispersive spectrometry and X-ray diffraction evidenced a microcrystalline structure of the expected composition with a (022̄5) texture. The fine-grained observed microstructure seems promising to improve thermoelectric properties and the texture should induce specific material properties.
The thermoelectric tensor component S11 and the relative electrical resistance along the binary axis of Bi2Te3 single crystals of p- and n-type are measured under hydrostatic pressure up to 9 GaP and temperatures from 20 to 300 °C. A P-T phase diagram of bismuth telluride is proposed, which is different from diagram, obtained under nonhydrostatic conditions.[Russian Text Ignored].
Nine of the twelve low-field galvanomagnetic coefficients of a p-type sample of Bi2 Te3 having a carrier concentration of 6.8×1018 cm-3 were measured at 4.2, 77, and 300°K. These results are combined with the Fermi-surface effective-mass tensor alpha obtained previously by de Haas-van Alphen experiments on the same sample to yield the relaxation time tau and its anisotropy. Reasonable success is obtained with the assumption of a single populated set of valence-band ellipsoids and a tensor form of tau. It is shown that either the tensor tau or the product alphatau for an ellipsoid is nonsymmetrical although alphatau for the crystal, as required by reciprocity, is symmetrical. Hall coefficients and longitudinal and transverse magnetoresistances for several orientations were also measured at 4.2 and 77°K in fields up to 160 kG. High-field saturation values of the longitudinal magnetoresistance were in reasonably good agreement with the results predicted from the mass and low-field-relaxation-time anisotropies. The saturation of the high-field Hall coefficient under both classical (ℏomegackT) and quantum-mechanical (ℏomegac>kT) conditions also agrees with the low-field findings and indicates, further, the absence of carriers from a second populated valence band for this sample.
Bismuth telluride films have been electrochemically deposited from solutions of Bi2O3 and TeO2 in diluted HNO3 (pH = 0.50) onto Ti sheet working electrodes at 293 K. A conventional three-electrode cell was used with a platinum wire counter electrode and Ag/AgCl (saturated KCl) reference electrode. Single-phase films of Bi2+xTe3-x solid solution have been prepared from E = -200 to +80 mV (versus Ag/AgCl). The films prepared at +20 less than or equal to E less than or equal to +60 mV exhibit strong {1 1 0} orientation, while those prepared at +60 < E less than or equal to +80 mV show remarkable {1 0 5} orientation. Both the a-axis and c-axis lengths are almost independent of the cathodic potential for E < -100 mV. Above -100 mV, the a-axis length gradually decreases and the c-axis length increases with cathodic potential, implying the Bi concentration in the Bi2+xTe3-x solid solution moves from the stoichiometric value. The films prepared at E < +20 mV show p-type conduction, while those prepared at +20 less than or equal to E less than or equal to +80 mV show n-type conduction. The largest Seebeck coefficient, S = -63 mu VK-1 (300 K), has been observed for the film deposited at E = +20 mV.
The thermoelectric properties of the p-type (Bi0.25Sb0.75)2Te3 doped with 8 wt. % excess Te and the n-type Bi2(Te0.94Se0.06)3 doped substantially with 0.07 wt. % I, 0.02 wt. % Te, and 0.03 wt. % CuBr which were grown by the Bridgman method at a rate of 6 cm/h were measured before and after annealing, where annealing was done in the temperature range from 473 up to 673 K for 2–5 h in a vacuum and a hydrogen stream. No annealing effect on the power factor was observed for the p-type specimen, but the as-grown p-type specimen exhibited a large power factor of 5.53×10−3 W/mK2 at 308 K and a low thermal conductivity of 1.21 W/mK. When the n-type specimen was annealed at 473 K for 2 h in a hydrogen stream, however, the power factor at 308 K increased significantly from 3.26×10−3 to 4.73×10−3 K−1 but its thermal conductivity then increased by about 3% from 1.26 to 1.30 W/mK. As a result, the maximum thermoelectric figure of merits Z at 308 K for the as-grown p- and annealed n-type specimens reached surprisingly great values of 4.57×10−3 K−1 and 3.67×10−3 K−1, respectively, with corresponding ZT values of 1.41 and 1.13. The present materials are sure to belong to the highest class in the Z and ZT values as bismuth telluride bulk compounds. © 2003 American Institute of Physics.
PREVIOUS publications from this Laboratory have described the progress made with bismuth telluride in connexion with thermoelectric refrigeration or generation. With a thermo-junction between p-type bismuth telluride and bismuth the maximum temperature difference obtained1 was 26?? C., and between p- and n-type bismuth telluride2 40??C. This corresponded with a figure of merit 0.0335 degree???1/2. Here ?? is the thermoelectric power, ?? the electrical conductivity, and K the thermal conductivity.
Bi2Te3 nanocrystals with various shapes such as sheet, rag, sheet-rod and rod shapes were synthesized via a solvothermal process based on the reaction between BiCl3 and Te in N,N-dimethylformamide at 100–180 °C at the present of organic addition and/or reducing agent. The products were characterized by X-ray diffraction, X-ray fluorescence (XRF) analysis, inductively coupled plasma-atomic emission spectroscopy (ICP-AES) and transmission electron microscopy (TEM). KBH4 was used as a reducing agent. Organic additive plays a key role in the formation of the lamellar structures. A possible formation mechanism is proposed.
The electronic structure and thermoelectric properties of Bi2Te3 single crystals and graphene-doped Bi2Te3 polycrystalline samples were investigated with the aid of first-principles calculations, X-ray diffraction, scanning electron microscopy, Rietveld refinement, and thermal and transport measurements. It was found that the p electrons from the Bi and Te atoms are responsible for the density of states near the Fermi level. Experimental results show that the graphene-doped Bi2Te3 exhibits lower thermal conductivity and has a higher figure-of-merit than the single crystals.
Lead lanthanum zirconate titanate (PLZT) ferroelectrics were produced in bulk ceramic and thin-film form from the same acetate precursor solutions in order to compare their electrical and physical properties. Bulk ceramics were hot pressed from chemically coprecipitated powders, and thin films were fabricated by spin coating on silver foil and platinum-coated silicon wafer substrates. A number of PLZT compositions were investigated, including ferroelectric memory materials near the morphotropic phase boundary with 2% La, memory and slim-loop ferroelectric x/65/35 (La/Zr/Ti) compositions with up to 12% La, as well as some antiferroelectric thin-film materials. Internal film stress from thermal expansion mismatch between films and substrates was found to contribute to differences in electrical properties and Curie temperatures between the thin film and bulk materials, as were interface layers between the films and substrates, mechanical clamping from the substrates and grain size.
A stable tunable diode laser which uses an electrooptic deflector incorporated into a Littrow-type external cavity as a wavelength tunable element is proposed and demonstrated. The deflector is fabricated by lead lanthanum zirconate titanate (PLZT) electrooptic ceramic with high quadratic electrooptic effect. Two half-wave plates and a large angle triangular electrode of PLZT electrooptic ceramic are designed to acquire a high frequency-voltage tuning ratio. By adjusting the voltage applied to the deflector, a large single-mode tuning range of 420 GHz (including mode hops) and a frequency-voltage tuning ratio of 840 GHz/kV have been achieved at 780.5 nm.
Bi0.5Sb1.5Te3 films were deposited by flash evaporation on silicon wafers with thermally grown SiO2 overlayers (SiO2/Si substrates). Their transport properties, i.e. the electrical conductivity, Hall coefficient, magnetoresistance coefficient, Hall mobility, Seebeck coefficient, thermal conductivity and thermoelectric figure of merit, were determined in the temperature range from 80 to 400 K. Investigations concerning the annealing behaviour in an argon atmosphere were carried out on films without and with protective layers. By optimization of manufacturing conditions, it was possible to obtain films of a high Hall mobility and with a thermoelectric figure z of merit of 2.9 × 10−3K−1 at room temperature. Since photolithographic structurization is possible these films will be useful as p-type materials for many applications in thermoelectric thin film devices in combination with microelectronic circuits on SiO2/Si wafers.
The thermoelectric, electric and structural properties of Bi2Te3 thin films grown by MOCVD have been investigated. The Seebeck coefficient shows that all the samples were n-type conductors decreasing from 213 to 129 μV/K when the carrier concentration increases from 9×1019 to 3×1020 cm−3. For high substrate temperature, good orientation of crystallites has been observed which can be directly related to the best values of Seebeck coefficient found. Hall effect has been studied in the temperature range from 110 to 450 K. The temperature dependence of the Hall mobility is found to be T−1 indicating lattice scattering. The good quality of Bi2Te3 thin films growth by MOCVD observed allow to confirm the high potential of these deposition method which can be turned to be suitable for growing thin films for thermoelectrical material production.
Thin films of bismuth telluride have been prepared by the reactive evaporation method. Film properties, such as conductivity, Hall effect, and thermoelectric power were studied in the temperature range from liquid nitrogen to 350 K. The films prepared were of n-type with a carrier concentration of 1.25 x 1020 at room temperature. The temperature dependence of the Hall mobility is found to be T−1.8 indicating lattice scattering.
The quantum spin Hall (QSH) phase is a time reversal invariant electronic state with a bulk electronic band gap that supports the transport of charge and spin in gapless edge states. We show that this phase is associated with a novel Z2 topological invariant, which distinguishes it from an ordinary insulator. The Z2 classification, which is defined for time reversal invariant Hamiltonians, is analogous to the Chern number classification of the quantum Hall effect. We establish the Z2 order of the QSH phase in the two band model of graphene and propose a generalization of the formalism applicable to multiband and interacting systems.
A water-soluble acetate process was developed for ferroelectric
PLZT materials. It can be readily adapted to the preparation of either
bulk ceramic materials or thin films. Compositions throughout the PLZT
system were prepared from water-soluble precursors consisting primarily
of the acetates of the individual metal oxides. The properties of the
thin films were evaluated and compared with those of the hot-pressed
powders
Electronic Refrigeration
- H J Goldsmid
Topological insulators in three dimensions
- C L Liang
- E J Mele
PLZT electrooptic materials and applications-a review
- G H Haertling