Showing papers on "Pyroelectricity published in 2011"
TL;DR: In this article, the electrocaloric properties of PbZr0.52Ti0.48O3 epitaxial films and 0.7PMN-0.3PT single crystals are measured and demonstrated enhanced low temperature refrigeration at morphotropic phase boundary compositions.
Abstract: The electrocaloric properties of PbZr0.52Ti0.48O3 (PZT) epitaxial films and 0.7Pb(Mg1/3Nb2/3)O3-0.3PbTiO3 (0.7PMN-0.3PT) single crystals are measured and demonstrated enhanced low temperature refrigeration at morphotropic phase boundary compositions. The results reveal large adiabatic cooling figures in ∼260 nm PZT films (11 K in 15 V) and 200 μm thick 0.7PMN-0.3PT single crystals (2.7 K in 240 V) at Curie transition temperatures and secondary cooling peaks at lower temperatures, near critical points. This is a very useful aspect of ferroelectric cooling elements to attain effective cooling over wide range of working temperatures in solid-state devices.
97 citations
TL;DR: In this article, a modified solid-state reaction method was used to produce rare-earth (RE) (Eu3+, Gd3+, Tb3+, and Dy3+)-doped BiFeO3 (BFO) ceramics, which adopted higher heating and cooling rates during sintering process.
Abstract: Rare-earth (RE) (Eu3+, Gd3+, Tb3+, and Dy3+)-doped BiFeO3 (BFO) ceramics were prepared by a modified solid-state reaction method, which adopted higher heating as well as cooling rates during sintering process. All the fabricated samples showed ferroelectric hysteresis loops with a remnant polarization of 21–35 μC/cm2. A piezoelectric coefficient (d33) of ∼48 pC/N was obtained and this value was showed to be composition independent. The pyroelectric properties of our samples were studied as a function of temperature. Generally, the pyroelectric coefficient slightly decreased with temperature, and this is attributed to the increase of electrical conduction at higher temperatures. Among the different doped BFO ceramics, Gd-doped samples exhibited the largest pyroelectric coefficient of 146 μC/m2K at room temperature. For the magnetic properties, slim hysteresis loop with remnant magnetizations of 0.016–0.044 emu/g were obtained in all the doped samples. Our results revealed that the RE-doped BFO ceramics posses an improvement in both the electrical and magnetic properties. On the basis of our studies, we demonstrate that RE-doped BFO is a potential candidate for magnetoelectric device applications.
85 citations
TL;DR: In this paper, Pb0.97La0.02(Zr0.95Ti0.05)O3 (PLZT) antiferroelectric films with a thickness of about 1.7 μm were deposited on Pt-buffered silicon substrates via a sol-gel process.
Abstract: (100)-oriented Pb0.97La0.02(Zr0.95Ti0.05)O3 (PLZT) antiferroelectric films with a thickness of about 1.7 μm were deposited on Pt-buffered silicon substrates via a sol-gel process. The room-temperature capacitance density of the films was above 195 nF/cm2 over the frequency range from 1 kHz to 1 MHz. The recoverable energy density was enlarged with increasing measurement field, and a maximum value of 12.4 J/cm3 at 1120 kV/cm was obtained at room temperature. From the temperature-dependent electric-field-induced polarization hysteresis loops, a maximum reversible adiabatic temperature change, ΔT = 8.5 °C, was obtained near the phase-transition temperature.
83 citations
TL;DR: In this article, 500 nm films of HA were spin-coated on silicon wafers and exhibited pyroelectricity, piezoelectricity, and photo effects.
Abstract: Hydroxyapatite (HA) is the major component of bone and is used in artificial form in many biomedical applications. It was once believed to have a centrosymmetric crystal structure. In theoretical and experimental studies published in 2005, it was shown to have a monoclinic P21 structure. In the work reported here, 500 nm films of HA were spin-coated on silicon wafers. The materials were not poled. They had a nonuniform polarization distribution and exhibited pyroelectricity, piezoelectricity, and photoeffects. Structures of this type may have a number of technological applications.
75 citations
TL;DR: Frequency-dependent polarization measurements confirmed that all of the materials are nonferroelectric; that is, the macroscopic polarization is not reversible, or "switchable", and type 1 non-phase-matchable.
Abstract: Two new noncentrosymmetric (NCS) polar oxide materials, Zn2(MoO4)(AO3) (A = Se4+ or Te4+), have been synthesized by hydrothermal and solid-state techniques. Their crystal structures have been determined, and characterization of their functional properties (second-harmonic generation, piezoelectricity, and polarization) has been performed. The isostructural materials exhibit a three-dimensional network consisting of ZnO4, ZnO6, MoO4, and AO3 polyhedra that share edges and corners. Powder second-harmonic generation (SHG) measurements using 1064 nm radiation indicate the materials exhibit moderate SHG efficiencies of 100 × and 80 × α-SiO2 for Zn2(MoO4)(SeO3) and Zn2(MoO4)(TeO3), respectively. Particle size vs SHG efficiency measurements indicate the materials are type 1 non-phase-matchable. Converse piezoelectric measurements resulted in d33 values of ∼14 and ∼30 pm/V for Zn2(MoO4)(SeO3) and Zn2(MoO4)(TeO3), respectively, whereas pyroelectric measurements revealed coefficients of −0.31 and −0.64 μC/m2 K at 5...
74 citations
TL;DR: In this article, the authors reported a large d31 piezoelectric coefficient and corresponding electromechanical coupling factor, Kp, for lead-free piezoceramics.
Abstract: We report a large d31 piezoelectric coefficient and corresponding electromechanical coupling factor, Kp, of 0.5Ba(Zr0.2Ti0.8)O3–0.5(Ba0.7Ca0.3)TiO3 (BCTZ50) and 0.68Ba(Zr0.2Ti0.8)O3–0.32(Ba0.7Ca0.3)TiO3 (BCTZ32) lead-free piezoceramics. The piezoelectric coefficient, d31, reaches a high value of 200 pC/N for BCTZ50 at room temperature which is comparable to the one of the soft PZT. This confirms the previously reported d33 for the same material. A useful way to achieve such performances at the expense of a smaller thermal budget is suggested, enabling better control of the ceramics composition and microstructure. Based on pyroelectric and ferroelectric hysteresis loops measurements, we show that such outstanding properties are likely due to the high flexibility of polarization under thermal and electric stresses.
69 citations
TL;DR: A novel vibrational isolation method for the pyroelectric detector is introduced for the reduction of acoustic noise and the absolute accuracy in energy is within ∼7%-9%.
Abstract: A new ultrahigh vacuum microcalorimeter for measuring heats of adsorption and adsorption-induced surface reactions on complex single crystal-based model surfaces is described. It has been specifically designed to study the interaction of gaseous molecules with well-defined model catalysts consisting of metal nanoparticles supported on single crystal surfaces or epitaxial thin oxide films grown on single crystals. The detection principle is based on the previously described measurement of the temperature rise upon adsorption of gaseous molecules by use of a pyroelectric polymer ribbon, which is brought into mechanical/thermal contact with the back side of the thin single crystal. The instrument includes (i) a preparation chamber providing the required equipment to prepare supported model catalysts involving well-defined nanoparticles on clean single crystal surfaces and to characterize them using surface analysis techniques andin situreflectivity measurements and (ii) the adsorption/reaction chamber containing a molecular beam, a pyroelectric heat detector, and calibration tools for determining the absolute reactant fluxes and adsorption heats. The molecular beam is produced by a differentially pumped source based on a multichannel array capable of providing variable fluxes of both high and low vapor pressure gaseous molecules in the range of 0.005‐1.5 × 10 15 moleculescm −2 s −1 and is modulated by means of the computer-controlled chopper with the shortest pulse length of 150 ms. The calorimetric measurements of adsorption and reaction heats can be performed in a broad temperature range from 100 to 300 K. A novel vibrational isolation method for the pyroelectric detector is introduced for the reduction of acoustic noise. The detector shows a pulse-to-pulse standard deviation ≤15 nJ when heat pulses in the range of 190‐3600 nJ are applied to the sample surface with a chopped laser. Particularly for CO adsorption on Pt(111), the energy input of 15 nJ (or 120 nJcm −2 ) corresponds to the detection limit for adsorption of less than 1.5 × 10 12 CO moleculescm −2 or less than 0.1% of the monolayer coverage (with respect to the 1.5 × 10 15 surface Pt atomscm −2 ). The absolute accuracy in energy is within ∼7%‐9%. As a test of the new calorimeter, the adsorption heats of CO on Pt(111) at different temperatures were measured and compared to previously obtained calorimetric data at 300 K. © 2011 American Institute of Physics.
63 citations
TL;DR: In this article, the polarization vs. electric field hysteresis loops of 0.9PMN-oriented 0.1PT single crystal at different temperatures (20 −110°C) were measured.
60 citations
TL;DR: The huge entropy change at the two-closely spaced high-temperature phase transitions in guanidinium perchlorate, together with the large crystal polarization, suggest a large electrocaloric effect, the property strongly desired for solid-state cooling applications.
Abstract: Dielectric, calorimetric, and X-ray diffraction methods have been employed to characterize the crystals of guanidinium tetrafluoroborate and guanidinium perchlorate, both built of two-dimensional honeycomb hydrogen-bonded sheets. The room-temperature ferroelectricity of these isosymmetric complexes (space group R3m) has been evidenced by the polarization switching in an external electric field and pyroelectric effect. The analysis of structural data as a function of temperature showed that the high values of spontaneous polarization of about 8.5 μC cm–2 originate mainly from the ionic displacements, while the exceptional thermally induced increase of polarization is related with the apparent weakening of the N–H···F/N–H···O hydrogen bonds at elevated temperatures. An excellent correlation between the donor–acceptor distance and the relative displacement of the ions in the crystal lattice along the polar direction has been found. The huge entropy change at the two-closely spaced high-temperature phase tran...
59 citations
TL;DR: Patterned thin films with various shapes and sizes are fabricated by photolithography, which sheds new light on the integration of PVDF-based electroactive polymers into organic microelectronic devices such as flexible pyroelectric/piezoelectric sensor arrays or non-volatile ferroelectric memory devices.
Abstract: Greatly enhanced energy density in poly(vinylidene fluoride-chlorotrifluoroethylene) [P(VDF-CTFE)] is realized through interface effects induced by a photo cross-linking method. Being different from nanocomposites with lowered dielectric strength, the cross-linked P(VDF-CTFE)s possess a high breakdown field as well as remarkably elevated polarization, both of which contribute to the enhanced energy density as high as 22.5 J · cm -3 . Moreover, patterned thin films with various shapes and sizes are fabricated by photolithography, which sheds new light on the integration of PVDF-based electroactive polymers into organic microelectronic devices such as flexible pyroelectric/piezoelectric sensor arrays or non-volatile ferroelectric memory devices.
55 citations
23 Aug 2011
TL;DR: Nalwa et al. as discussed by the authors reviewed the current research status of ferroelectric devices based on poly(vinylidene fluoride-trifluoroethylene) [P(VDF-TrFE) copolymers.
Abstract: The discovery of the piezoelectric properties of poly(vinylidene fluoride) (PVDF) by Kawai [Kawai, 1969], and the study of its pyroelectric and nonlinear optical properties [Bergman et al, 1971; Glass, 1971] led to the discovery of its ferroelectric properties in the early 1970s Since that time, considerable development and progress have been made on both materials and devices based on PVDF This work helped establish the field of ferroelectric polymer science and engineering [Nalwa, 1995a] There are many novel ferroelectric polymers, such as poly(vinylidene fluoride) (PVDF) copolymers, poly(vinylidene cyanide) copolymers, odd-numbered nylons, polyureas, ferroelectric liquid crystal polymers and polymer composites of organic and inorganic piezoelectric ceramics [Nalwa, 1991 and Kepler & Anderson, 1992 as cited in Nalwa, 1995b; Nalwa, 1995a] Among them, PVDF, and its copolymers are the most developed and promising ferroelectric polymers because of their high spontaneous polarization and chemical stability Ferroelectricity is caused by the dipoles in crystalline or polycrystalline materials that spontaneously polarize and align with an external electric field The polarization of the dipoles can be switched to the opposite direction with the reversal of the electric field Similar to inorganic ferroelectric materials such as PbZr05Ti05O3 (PZT) and SrBi2Ta2O9 (SBT), organic ferroelectric materials exhibit ferroelectric characteristics such as Curie temperature (the transition temperature from ferroelectrics to paraelectrics), coercive field (the minimum electric field to reverse the spontaneous polarization) and remanent polarization (the restored polarization after removing the electric field) However, the low temperature and low fabrication cost of organic ferroelectric materials enable them to be used in a large number of applications, such as flexible electronics In this chapter, the discussion is focused on poly(vinylidene fluoride-trifluoroethylene) [P(VDF-TrFE)], one of the most promising PVDF ferroelectric copolymers The main objective of this chapter is to describe the ferroelectric properties of P(VDF-TrFE) copolymer and review the current research status of ferroelectric devices based on this material The chapter is divided in six sections The first section introduces the topic of organic ferroelectrics The second section describes the material properties of the ferroelectric phase of P(VDF-TrFE) including phase structures, surface morphology, crystallinity and molecule chain orientation Next, the electrical properties such as polarization, switching current, etc
TL;DR: In this paper, the authors investigated the dielectric, AC conductivity, pyroelectric and piezoelectric properties of HA-40 wt% BaTiO3 composites.
Abstract: In order to mimic the electrical properties of natural bone, the present work investigated the dielectric, AC conductivity, pyroelectric and piezoelectric properties of HA-40 wt% BaTiO3 (HA-26 vol% BaTiO3) and HA-60 wt% BaTiO3 (HA-44 vol% BaTiO3) composites. Multistage spark plasma sintering was used to achieve the desired combination of properties. The electrical parameters were measured as a function of temperature and frequency. The values of dielectric constant and loss for both the developed composites, measured at room temperature and at 1 KHz frequency was 21, 38 and 0.01 and 0.02, respectively. The AC conductivity for both the composites is found to be of the order of 10−10 and 10−9 (Ωcm)−1, measured under similar conditions. Activation energy calculated from σac vs. temperature plot for HA-40 wt% BaTiO3 is 0.50 eV. The room temperature pyroelectric coefficients for both the compositions are 2.35 and 21 μC/m2K, respectively. The piezoelectric coefficient values (d33) for both the compositions are ...
23 Aug 2011
TL;DR: In this article, the authors studied the effect of spontaneous polarization on the hysteresis loop of a ferroelectric capacitor and found that the leakage can have a significant impact on the performance of the capacitance.
Abstract: Ferroelectrics are multifunctional materials exhibiting a host of appealing properties resulting from the presence of the spontaneous polarization, which is a polarization occurring in the absence of an applied electric field, due to a structural transformation taking place at a certain temperature (Uchino, 2000; Lines & Glass, 1977). Among the most important properties are: ferroelectricity-the ability to switch the spontaneous polarization by the application of a suitable electric field; piezoelectricity-the ability to produce a voltage by the application of a mechanical stress, or the ability to change the strain by applying a voltage; pyroelectricity-the ability to generate current when heated/cooled; birefringencedifferent refraction indices along the polar axis and on other crystalline directions, etc. It is thus of no wonder that ferroelectric materials, especially those with perovskite structure (e.g. Pb(Zr,Ti)O3, known as PZT, or BaTiO3) , quickly found a lot of applications in the electronic industry, security, medicine, different type of automations, etc. In most of the applications the ferroelectrics are used as capacitors, either as bulk ceramics or single crystals or as thin films of polycrystalline or epitaxial quality (Izyumskaya et al., 2008; Dawber et al. 2). Also, most of the applications are based on the application of an external voltage on the ferroelectric capacitor, leading unavoidable to the occurrence of a leakage current. If in the case of bulk ferroelectrics, especially in the form of ceramics, the leakage is usually negligible, only the currents due to polarization variations being of significant value (e.g. pyroelectric or reversal currents), in the case of the thin films the leakage currents can be so large that they hidden any contribution from polarization variation. This fact is not acceptable in applications which are based on reading currents due to polarization changes under the influence of an external voltage, as is the case for the read/write process in nonvolatile ferroelectric memories (Scott J. F., 2000). Solutions to reduce the leakage can be found only if the conduction mechanism is correctly understood, as well as the impact of leakage on other macroscopic properties. For example, the leakage can have a significant impact on the hysteresis loop, considering that the loop is obtained by the integration of the charge released during the polarization switching. A large leakage current, over-imposed on the switching current will alter the hysteresis, masking the presence of ferroelectricity in the analyzed sample. Therefore, the study of the charge transport in ferroelectric thin films is of high importance for all the applications using ferroelectric capacitors subjected to an applied external voltage, in order to indentify the conduction mechanisms responsible for the leakage current (Chentir et al. 2009; Pabst et al. 2007; Meyer et al., 2005; Horii et al., 1999). Traditionally, the possible conduction mechanisms in ferroelectric thin films are divided in two major classes (Pintilie L. & Alexe M., 2005; Pintilie L. et al., 2005):
TL;DR: The PZT sheet was further etched to produce deeper cavities and a smaller electrode width to induce lateral temperature gradients on the sidewalls of cavities under homogeneous heat irradiation, enhancing the temperature variation rate.
Abstract: This paper proposes the idea of etching PZT to improve the temperature variation rate of a thicker PZT sheet in order to enhance the energy conversion efficiency when used as pyroelectric cells. A partially covered electrode was proven to display a higher output response than a fully covered electrode did. A mesh top electrode monitored the temperature variation rate and the electrode area. The mesh electrode width affected the distribution of the temperature variation rate in a thinner pyroelectric material. However, a pyroelectric cell with a thicker pyroelectric material was beneficial in generating electricity pyroelectrically. The PZT sheet was further etched to produce deeper cavities and a smaller electrode width to induce lateral temperature gradients on the sidewalls of cavities under homogeneous heat irradiation, enhancing the temperature variation rate.
TL;DR: In this article, a complete manufacturing process for obtaining pyroelectric thin film sensors composed of a blend of PVDF and PMMA polymers was presented, which consisted of a stack of metallic (Ti/Pt) electrodes around an active pyro electric layer and are able to detect a temperature variation through the pyrotechnic effect.
Abstract: This paper will present a complete manufacturing process for obtaining pyroelectric thin film sensors composed of a blend of PVDF and PMMA polymers. These sensors comprise a stack of metallic (Ti/Pt) electrodes around an active pyroelectric layer and are able to detect a temperature variation through the pyroelectric effect. Deposition is achieved with solution using a spin-coating and hot plate drying method. Addition of PMMA is a technique for promoting the crystallization of PVDF in the β phase, with one of the PVDF polymer chain conformations producing a ferroelectric behaviour. Analysis of the role of the solvent evaporation rate has been carried out with FTIR and indicates that low temperature evaporation (below 70 °C) leads to the presence of β phase in the material. Polarization curve measurement also indicates the ferroelectric behaviour of deposited layers. Finally a thermal transient response indicates a pyroelectric coefficient of 20 μC m−2 K−1 which is close to the bulk material value (27 μC m−2 K−1).
TL;DR: In this article, the authors used molecular dynamics with a first-principles-based shell model to study pyroelectricity in lithium niobate and found that the primary pyro electric effect is dominant.
Abstract: We use molecular dynamics with a first-principles-based shell model potential to study pyroelectricity in lithium niobate. We find that the primary pyroelectric effect is dominant, and pyroelectricity can be understood simply from the anharmonic change in crystal structure with temperature and the Born effective charges on the ions. This opens an experimental route to study pyroelectricity, as candidate pyroelectric materials can be studied with x-ray diffraction as a function of temperature in conjunction with theoretical effective charges. We also predict an appreciable pressure effect on pyroelectricity, so that chemical pressure, i.e., doping, could enhance the pyroelectric and electrocaloric effects.
TL;DR: For example, tourmaline growth on a seed crystal occurs only if separate tourmalines-forming components (monocrystalline corundum and quartz bars) are used as charge.
Patent•
16 Mar 2011
TL;DR: In this article, a ternary system relaxation ferroelectric single crystal material, PIMNT, has been presented, which is an improved Bridgman method and comprises the following steps of: processing raw materials, melting by raising the temperature, and performing crucible degrowth and crystal cooling growth.
Abstract: The invention discloses a ternary system relaxation ferroelectric single crystal material. The material comprises the following chemical components: xPb(In1/2Nb1/2)O3-yPb(Mg1/3Nb2/3)O3-(1-x-y)PbTiO3, wherein the x is equal to 0.1-0.45, and the y is equal to 0.1-0.5. A preparation method of the single crystal material PIMNT is an improved Bridgman method and comprises the following steps of: processing raw materials, melting by raising the temperature, and performing crucible degrowth and crystal cooling growth. The prepared single crystal material overcomes the defects of over low Curie point of PMNT single crystals, difficult crystallization and difficult batch growth of the PINT single crystals in the prior art, has high piezoelectric performance and pyroelectric performance, higher temperature stability and wide application prospect and adds a new product in the field.
TL;DR: A nonlinear thermodynamic theory is used to analyze the influence of thermal stresses on electrocaloric (EC) properties of (001)-textured polycrystalline monodomain BaTiO3, Ba0.6Sr0.4, and PbTiO 3 films on integrated circuit-compatible substrates Si, c-sapphire, and a-Sapphire as discussed by the authors.
Abstract: A nonlinear thermodynamic theory is used to analyze the influence of thermal stresses on electrocaloric (EC) properties of (001)-textured polycrystalline monodomain BaTiO3, Ba0.6Sr0.4TiO3, and PbTiO3 films on integrated circuit-compatible substrates Si, c-sapphire, and a-sapphire. The results show that the EC response can depend strongly on the film growth temperature TG which can shift the maximum in EC properties to a working temperature of interest. For BaTiO3 films on Si, the thermal stresses are sufficient to shift the zero-field Curie temperature TC near to room temperature, resulting in a strong enhancement of the EC properties as compared to the bulk material.
TL;DR: In this article, the authors investigated the energy harvesting capacity of pyroelectric samples fabricated in our laboratory and commercially available pyro electric elements/transducers by capturing thermal energy of pavements.
Abstract: Power harvesting is the process of extracting useful electrical energy from ambient low grade energy sources such as solar energy, mechanical energy, and thermal energy using smart materials as transducers. These materials have the ability to convert one form of energy into another. This paper aims at thermal-electrical energy converters based on a pyroelectric effect for energy harvesting, and examines its possible use in ultralow power devices and sensor modules. The present work investigates theoretically the energy harvesting capacity of pyroelectric samples fabricated in our laboratory and commercially available pyroelectric elements/transducers by capturing thermal energy of pavements. The single- and polycrystalline elements: triglycine selenate; lithium tantalate; modified lead zirconate titanate; modified lead titanate; modified lead metaniobate; and pyroelectric polymer nanocomposites such as Portland cement; nanocarbon fibers; polymer-lithium tantalate embedded with silver nanoparticles; and others were characterized for applicable performance parameters. The modeling and numerical simulation of energy harvesting capacity of these samples with the available pavement's temperature-profile data over an extended period of time were investigated. The results indicate that the electrical energy harvesting via pyroelectricity is a feasible technique for powering autonomous low-duty electric devices.Based on our analysis of a single electric-energy harvesting unit, the triglycine selenate elements shall perform better than others with regard to the amount of voltage and energy densities extracted with respect to time. Possible future work and concepts of developing promising multidomain energy harvesters or hybrid harvesters are also briefly discussed.
TL;DR: In this paper, Lanthanum modified PZT (PLZT) ceramics were prepared with nano powders obtained by the sol gel method and its piezoelectric and pyroelectric behaviour was studied.
Abstract: Lanthanum modified PZT (PLZT) ceramics were prepared with nano powders obtained by the sol gel method and its piezoelectric and pyroelectric behaviour was studied. The piezoelectric properties of the sol gel derived ceramics were compared with the ones prepared by the conventional oxide route. It was found that although the figures of merit of the sol gel derived ones were slightly better (10–15% increase), because of its higher density with respect to conventional ones. The pyroelectric properties of PLZT needs special mention because of its high detectivity and low noise levels. The results are tabulated in the paper and it indicates great figures of merit.
TL;DR: In this paper, relaxor-based ferroelectric single-crystalline materials of the solid solution system of Pb(B 1, 82)03(6): Mg 2+, In 3+..., B 2 : Nb 5+, Ta'"...) and PbTiO 3, which have already been considered as next-generation piezoelectric materials with superhigh pyroelectric effect.
Abstract: We report in this paper our discovery of remarkably excellent pyroelectric performances in the widely investigated, but still not weH understood, relaxor-based ferroelectric single-crystalline materials of the solid solution system of Pb(B 1 , 82)03(6): Mg 2+ , In 3+ ..., B 2 : Nb 5+ , Ta'" ...) and PbTiO 3 , which have already been considered as next-generation piezoelectric materials with superhigh piezoelectric effect. Values of pyroelectric coefficient as high as 17.2 × 10 ―4 C/m 2 K and of figure of merit for detectivity of 40.2 x 10 ― 5 Pa ―1/2 can be produced in the poled crystals specincaHy in the crystaHographic direction along the spontaneous polarization, i.e., the direction in the rhombohedral phase. They show great potential as novel pyroelectric materials for wide applications in infrared (IR) detectors and thermal imagers. Commercialized IR detector prototypes have atso been fabricated with the spectro detectivity of 1.07 x 10 9 cm Hz 1/2 W ―1 , which nearly doubles that of conventional LiTaO 3 single-crystal-based commercialized IR detectors with similar detection mode. The relations :j among crysttU composition, iron doping, orientation, phase structure, domain configuration, and pyroelectric property, as well as between thermal parameters and dietectnc properties wiU also be presented here. They address the physics behind and the IR-sensor application using the strong pyroelectric effect of this complicated but promising family of pyroelectric materials. Examples are given for Pb(Mg 1/3 Nb 2/3 )O 3 -PbTiO 3 (PMNT) and ternary Pb(In 1/2 Nb 1/2 )O 3 -Pb(Mg 1/3 Nb 2/3 )O 3 -PbTiO 3 .
TL;DR: In this article, a typical thermodynamic energy cyclic path is proposed for polar dielectric as cooling devices to experience, with the influence of temperature taken into consideration, the free energy of a thermal electrical coupling system of polar liquid dielectrics is formulated, and the variation of temperature and entropy, the absorption of heat, and work under different electric fields are calculated for BaTiO3, Pb(ZrxTi1-x)O3 and P(VDF-TrFE), and water.
Abstract: Polar dielectric based cooling devices are modeled as a system with two degrees of freedom and represented by either an entropy-temperature or electric displacement-electric field plane. A typical thermodynamic energy cyclic path is proposed for polar dielectric as cooling devices to experience. With the influence of temperature taken into consideration, the free energy of a thermal electrical coupling system of polar dielectrics is formulated, and the variation of temperature and entropy, the absorption of heat, and the work under different electric fields are calculated for BaTiO3, Pb(ZrxTi1-x)O3, P(VDF-TrFE), and water. And the simulation results obtained agree well with the recently published experimental data [B. Neese, et al., Science 321, 821 (2008)]. It is, therefore, suggested that the high polar liquid dielectrics may possess a large electrocaloric effect.
TL;DR: In this paper, an all-optical method to measure the pyroelectric coefficient p of electro-optic crystals was proposed, where the birefringence variation δΔn of the crystal as a function of its temperature T was obtained using a Senarmont phase-compensation configuration.
Abstract: We report an all-optical method to measure the pyroelectric coefficient p of electro-optic crystals. Through this technique, we first acquire the birefringence variation δΔn of the crystal as a function of its temperature T, both in closed and open-circuit conditions, using a Senarmont phase-compensation configuration. Then the pyroelectric field is deduced from the difference between these two measurements, so it leads to the material spontaneous polarization change, whose derivative with respect to the temperature finally gives p. This technique is applied on congruent and stoichiometric lithium niobate.
TL;DR: In this paper, the doping and grain size effects on dielectric and dc bias field-induced pyroelectric properties were systemically investigated, and they showed that the increase of the content of acceptors and the adding of donors simultaneously could contribute to the development of high pyro electric properties of the TiO3 ceramics for uncooled infrared detector.
Abstract: Ba0.7Sr0.3TiO3 (BST) ceramics with different dopants and various grain sizes were fabricated by the solid-state reaction process, and the doping and grain size effects on dielectric and dc bias field-induced pyroelectric properties were systemically investigated. When acceptors were added, the dielectric loss of the BST was decreased effectively, whereas the pyroelectric coefficient was decreased for the broadening of dielectric constant peaks. With the increase of the content of acceptors and the adding of donors simultaneously, the decrease of pyroelectric coefficient caused by the doping effect could be weakened. The dielectric and dc bias field-induced pyroelectric properties were also affected by the grain size effects dramatically. In this paper, the best pyroelectric coefficient of 105 × 10−8 C/cm2 °C and figure-of-merit of 22 × 10−5 Pa−0.5 could be obtained when the grain size was 1 µm. The systemic investigation of doping and grain size effects would contribute to the development of high pyroelectric properties of BST for uncooled infrared detector.
TL;DR: In this article, a network microstructure with large grains isolated from one another by the regions constituted with the agglomerated fine grains of CCTO ceramics fabricated by sol-gel processing has been investigated.
TL;DR: In this article, a relaxor-based ferroelectric single crystal with a rhombohedral perovskite-type structure has been grown by the modified Bridgman technique, and the as-grown PIMNT (21/49/30) crystal shows high phase transition temperature from ferro-electric rombohedral to tetragonal (T RT ∼125) and high Curie temperature (T C ∼180) higher than what was found for the 0.71Pb(Mg 1/3 Nb 2/3 )O 3 [PMNT (
TL;DR: In this paper, the electric-field-induced ferroelectric (FEIN) to antiferroelectric phase transition was reported, which is tuned by the poling temperatures in 0.89Bi0.5Na 0.5NbO3 (0.06BaTiO3-0.05K0.
Abstract: We report the electric-field-induced ferroelectric (FEIN) to antiferroelectric (AFE) phase transition that is tuned by the poling temperatures in 0.89Bi0.5Na0.5TiO3-0.06BaTiO3-0.05K0.5Na0.5NbO3 (0.89BNT-0.06BT-0.05KNN) ceramics. Phase transition and pyroelectric behaviors of the ceramics were investigated as functions of temperature and electric field. Pyroelectric coefficient peaks of (3 ∼ 6.5) × 10−8 C cm−2 K−1 are detected at about 10 °C above the poling temperatures for the samples poled at different temperatures. The poling temperature tuned pyroelectric behaviors are attributed to the FEIN to AFE phase transition when the temperature increases.
01 Jan 2011
TL;DR: In this paper, it was shown that perovskite-phase metal oxides exhibit a variety of interesting physical properties which include ferroelectric, dielectric, pyroelectric and piezoelectric behavior.
Abstract: Perovskite-phase metal oxides exhibit a variety of interesting physical properties which include ferroelectric, dielectric, pyroelectric, and piezoelectric behavior.1-4 Specifically, linear dielectric materials exhibit linear polarization behavior as a function of applied field. Ferroelectric ceramics are dielectrics with a permanent electric dipole, which can be oriented upon the application of an electric field. Pyroelectric materials yield a spontaneous polarization, but the direction of such polarization cannot be reversed upon application of an electric field. Piezoelectrics either exhibit an electrical charge when mechanically stressed or undergo mechanical deformation upon the application of an electric field. In general, these various properties arise from the crystal symmetry adopted by these materials.5,6
05 Jun 2011
TL;DR: In this paper, shape memory alloys (SMA) are used to convert thermal energy into electrical energy with relatively good efficiency by coupling SMA with piezoelectric materials.
Abstract: The increasing demand in alternative energy sources for low-power electronics gives rise to substantial research activity in the field of energy harvesting devices in recent years. Among the different energy sources, thermal sources can be used to produce electrical energy by means of thermoelectric materials, which exploit Seebeck effect [1], or pyroelectric materials [2]. However, thermoelectric devices require large spatial temperature gradients in order to be efficient. In much the same way, pyroelectric materials are inefficient with slow variations of ambient temperature. Nevertheless there is a possibility to convert indirectly thermal energy into electrical energy through mechanical transformations [3]. Taking advantage of the large mechanical deformation (up to 10% [4]) of shape memory alloys (SMA) in the vicinity of their thermally induced phase transition one can convert this mechanical energy into electrical energy with relatively good efficiency by coupling SMA with piezoelectric materials.