Value Of Pyroelectric Coefficient Research Articles

Peculiarities of the electrocaloric effect in relaxors

A comprehensive study and detailed analysis of pyroelectric and electrocaloric effects in relaxor ferroelectrics based on lead magnesium niobate as a promising object for such investigations have been carried out. It was found that even at the maximum values of pyroelectric coefficients the electrocaloric response inextricably linked with the pyroelectric effect does not exceed 1 °C in the temperature range from 10 to 60 °C under DC electric field up to 60 kV/cm. These conditions are the most demanded for the operation of electrocaloric cooling devices. Vision for the future as to increasing the efficiency of the main elements for such devices is discussed.

Effect of lanthanum dopant on pyroelectric characteristics of lead germanate (Pb5Ge3O11) single crystals

In this article, the behavior of pyroelectric coefficient and spontaneous polarization with temperature have been studied for pure (LG), 0.5 wt% (LG1) and 1 wt% (LG2) lanthanum doped lead germanate (Pb5Ge3O11) single crystals. These crystals were grown by method of controlled cooling of the melt. The pyroelectric coefficient of grown crystals was measured over a temperature range 40–300 °C, which shows a change in sign negative to positive for LG and LG1 while for LG2 it shows only negative sign for a said temperature range. The observed results of pyroelectricity and spontaneous polarization in pure and doped materials are discussed. The comparative study of room temperature values of pyroelectric coefficient measured by various methods, spontaneous polarization and figure of merit is presented in this paper.

Lead-free (Ba0.88Ca0.12)(Ti0.94Sn0.06)O3 piezoceramics: A comprehensive analysis of the phase evolution and enhancement of electrical properties induced by high energy ball milling

The study reveals that high-energy ball milling can be employed to induce controlled phase evolution in lead-free (Ba0.88Ca0.12)(Ti0.94Sn0.06)O3(BCST) ceramics. These piezoceramics were fabricated through solid-state sintering route using nanopowders produced by high-energy milling over durations varying from 5 to 30 h. Rietveld refinements confirm the co-existence of orthorhombic (O)-tetragonal (T) phases in the ceramics with their relative proportions systematically changing with the milling duration. The milling technique demonstrates its capability of enhancing the Curie temperature (Tc) appreciably –BCST's low Tc being a serious drawback for not making it a strong contender for replacing widely used PZT in piezoelectric industry. Additionally, the study shows the possibility of enhancing the high pyroelectric coefficient value by 260% and electrostrictive response to as high as 0.048 m4C-2 by only mechanical milling without any change in the ceramic composition. These observed values of pyroelectric and electrostrictive responses are much higher than even those of Pb-based materials.

Effect of electric field assisted crystallisation of PVDF-TrFE and their functional properties

Uniform thin films of poly(vinylidene fluoride)-trifluoroethylene copolymers were spin-coated and their functional electrical properties were investigated after corona poling. The copolymers were poled in the gel state at room temperature (RT) without stretching or annealing treatment. This E-field crystallisation processing method at RT leads to the formation of improved ferroelectric and pyroelectric properties in the investigated thin films. That processing method has great potential for ferroelectric material coatings on thermally highly sensitive substrates. The selected composition (∼1 µm thick composites of 65/35 mol% PVDF-TrFE) of the copolymer produced a pyroelectric coefficient value of 36 ± 3 µC/m2K1, a dielectric constant of 9, and a dielectric loss of about 0.018 at a frequency of 1 kHz under ambient conditions.

Electro-Optical Properties of Sputtered Calcium Lead Titanate Thin Films for Pyroelectric Detection.

We report the deposition and characterization of calcium lead titanate (PCT) thin films for pyroelectric detectors. PCT films of thicknesses ranging from ~250 to 400 nm were deposited on both silicon and Si/SiN/Ti/Au substrates at 13 mTorr pressure by 200W radio frequency sputtering in an Ar + O2 environment. Substrates were kept at variable temperatures during the deposition. The PCT films were annealed at various temperatures in an O2 environment for 15 min. X-ray diffraction results confirm the polycrystalline nature of these films. Energy dispersive spectroscopy function of scanning electron microscope showed that the films are stoichiometric (Ca0.43Pb0.57) TiO3 (Ca/Ti = 0.5, Pb/Ti = 0.66). Temperature dependence of capacitance, pyroelectric current, and pyroelectric coefficient was investigated for different PCT films. Our results show that films deposited at 550 °C and 600 °C demonstrate better quality and larger values of the pyroelectric coefficient. On the other hand, the capacitance fabricated on the PCT films at 550 °C showed the highest value of pyroelectric current and pyroelectric coefficient which were 14 pA and at 30 °C was ~2 µC/m2K respectively at a higher temperature. In addition, we used density functional theory to determine the atomic and band structure, real and imaginary parts of dielectric constant and refractive index, and absorption and reflection constants with energy.

Lead-free 0.95(K0.6Na0.4)NbO3-0.05(Bi0.5Na0.5)ZrO3 ceramic for high temperature dielectric, ferroelectric and piezoelectric applications

Environment-friendly 0.95(K0.6Na0.4)NbO3-0.05(Bi0.5Na0.5)ZrO3(KNN-BNZ) ceramic have been prepared via high energy ball-milling followed by sintering. The effect of sintering temperature on the structural and piezoelectric properties has been studied and optimization of sintering temperature was carried out. X-ray diffraction (XRD) reveals the coexistence of tetragonal and rhombohedral phases for all the samples sintered at different temperatures. The ceramic sample sintered at 1150 °C showed high piezoelectric charge coefficient (d33 = 340 pC/N) with uniform and dense grains. Relaxor type ferroelectric behaviour with Curie phase temperature around 347 °C (at 1 kHz) was obtained. Well saturated and fatigue resistant P-E hysteresis loops with a remnant polarization (Pr) of 19.58 μC/cm2 and a coercive field (Ec) of 14.24 kV/cm were obtained at room temperature. A high value of pyroelectric coefficient (p ∼1855.1 μC m−2oC−1) was obtained in the temperature range 90–150 °C suitable for pyroelectric applications. Further, piezoelectric generator was fabricated using KNN-BNZ ceramic. An open circuit voltage of ∼6.2 V was generated from the device under periodic compressive force of 2 kgf. Thus, 0.95(K0.6Na0.4)NbO3-0.05(Bi0.5Na0.5)ZrO3 ceramic can serve as promising material for various electromechanical, ferroelectric and pyroelectric based devices.

Electrocaloric effect and pyroelectric energy harvesting in diffuse ferroelectric Ba(Ti1-xCex)O3 ceramics

In the present work Ba(Ti1-xCex)O3 ceramics are prepared through a standard solid-state sintering process. Crystal structures, dielectric properties, ferroelectric properties and electrocaloric effects are exactly studied. Ce4+ ions cannot entirely enter the position of Ti4+, so some impure phases are generated. The diffusivity of phase transition is strengthened by substituting Ti4+ with Ce4+ cations. The maximal pyroelectric coefficient decreases, and the extent of corresponding temperature deviating from the dielectric peak temperature to higher temperature increases with increasing the content of cerium cations. The adiabatic temperature change and isothermal entropy change display the same tendency as that of the pyroelectric coefficient. The Ba(Ti0.9Ce0.1)O3 ceramic shows the largest adiabatic temperature change of 0.41 K and the largest isothermal entropy change of 0.45 J/(kg·K) among the ceramics. Accordingly, the adiabatic temperature change responsivity is 0.090 × 10−6 K·m/V, and the isothermal entropy change responsivity is 0.100 × 10−6 J·m/(kg·K·V). For individual composition, the absolute value of pyroelectric coefficient decreases with increasing the magnitude of applied electric field, and the temperature of maximal pyroelectric coefficient deviates from the dielectric peak temperature shifts to higher temperature. Ba(Ti0.9Ce0.1)O3 ceramics show the largest pyroelectric energy density of 0.14 J/cm3 among all compositions.

Raman study of pyroelectric and injected charge induced fields in PLZT 8/65/35 ceramics

Electric fields of different nature induced in lanthanum doped lead zirconate-titanate (PLZT) ceramics were studied by confocal Raman microscopy. Temperature dependence of the pyroelectric field was determined and the value of pyroelectric coefficient was estimated. An appearance of additional line in Raman spectrum of PLZT after e-beam irradiation was revealed and its spatial distribution was studied. The origin of this spectral line was discussed in terms of defects formation and phase transitions.

Pyroelectric performance of [Bi0.48Na0.4032K0.0768]Sr0.04(Ti0.975Nb0.025)O3 ceramics

In the present work, the pyroelectric performance of [Bi0.48Na0.4032K0.0768]Sr0.04(Ti0.975Nb0.025)O3 (BNT-2.5Nb) ceramics is investigated. At room temperature, the value of pyroelectric coefficient found as 13.2 × 10−4 C/m2 K which is higher than many lead-free ferroelectric materials. Further, the pyroelectric figures of merit (FOMs) for detectivity (Fd), voltage responsivity (Fv), current responsivity (Fi), and energy harvesting (Fe*) are calculated. BNT-2.5Nb ceramics show pyroelectric open circuit voltage as 0.45 V when it was exposed to temporal temperature gradient. This work result indicates that the Nb-doping in Bi0.5Na0.5TiO3-based composition can be beneficial for lead-free pyroelectric device applications.

Dielectric, pyroelectric and ferroelectric properties of lead-doped Sn2P2S6 crystals

ABSTRACTThe dielectric, pyroelectric and ferroelectric properties of (PbySn1−y)2P2S6 (y = 0.1, 0.2 and 0.3) single crystals were analysed in the vicinity of phase transition. The measurements were done covering a wide range of frequency (20 Hz to 1 MHz) and temperature (30350 K) range. Structural phase transition temperature decreases with increased lead concentration and evokes the broadening of the dielectric anomaly. The features of this phase transition are discussed and related to stereoactivity of Sn2+ ions and fluctuations of the concentration of Pb2+ ions. Pyroelectric measurements were performed from 190 K to 325 K during the heating cycle. These investigations showed that an increase of lead concentration does not affect the maximum value of pyroelectric coefficient, and the maximum values of pyroelectric coefficients γmax which (in the vicinity of the phase transition temperature) are nearly equal to 250 nC cm−2 K−1 for all the compositions. The temperature evolution of polarization hysteresis loops proved crystals being ferroelectrics.

Pyroelectric performance of (Ba0.825+xCa0.175-x)(Ti1-xSnx)O3 lead free ceramics

The pyroelectric properties of (Ba0.825+xCa0.175-x)(Ti1-xSnx)O3 ceramics with x = 0.0625, 0.0875 and 0.100 were investigated. Samples were fabricated using solid state reaction route and were exposed to IR lamp periodically to recorded open circuit voltage. Peak value of open circuit voltage was 0.8 V, 0.70 V and 0.53 V for x = 0.0625, 0.0875 and 0.1 samples, respectively. P–E loops were recorded for all the compositions under study. Further pyroelectric coefficient was estimated using P–E loops data. The values of pyroelectric coefficient estimated as 5.70 × 10−4C/m2 K, 5.5 × 10−4C/m2 K and 5 × 10−4C/m2 K for x = 0.0625,0.0875 and 0.1 samples.

Giant piezoelectric behavior in relaxor ferroelectric environment friendly Na0.52K0.44Li0.04Nb0.84Ta0.10Sb0.06O3 ceramics for high temperature applications

Lead free Na0.52K0.44Li0.04Nb0.84Ta0.10Sb0.06O3 (NKLNTS) ferroelectric ceramic was synthesized to replace lead based ceramics with high piezoelectric performance for application in sensors, transducers and other electronic devices. The synthesis of NKLNTS ceramic was carried out using solid state reaction technique and the sintering temperature was taken to be 1090 °C. The structural phase of synthesized ceramic was found to be pure perovskite as observed from powder X-ray diffraction. FE-SEM micrographs revealed the formation of homogeneous microstructure with well defined grains. The excellent dielectric response with a high value of Curie temperature (in the range 305–315 °C for all frequencies) and low dielectric loss (0.06 at high frequency of 2 MHz at room temperature) was observed. J–E curve was analyzed and conduction mechanism in NKLNTS ceramic was found to be Ohmic. A ‘Displacement–Voltage’ butterfly loop was traced and a very large value of piezoelectric charge coefficient (d33* ~ 754 pm/V) was obtained. P–E hysteresis loops were traced to study ferroelectric behavior of NKLNTS ceramic. The value of pyroelectric coefficient was obtained to be very high ∼ 1921.9 µCm− 2 °C−1. Fatigue test was performed over 107 switching cycles and fatigue free nature of NKLNTS ceramic was observed. Remanent hysteresis task was performed to determine the true-remanent polarization of NKLNTS ceramic. Time-dependent compensated hysteresis task was carried out which revealed resistive leakage free nature of the ceramic.

Electrocaloric effect in relaxor ferroelectric Ba(Ti1-xYx)O3-x/2 ceramics over a broad temperature range

Crystal structures, dielectric, ferroelectric properties and electrocaloric effects of hetero-valent substituted Ba(Ti1-xYx)O3-x/2 ceramics were studied in the present work. The polar space group of P4mm was adopted based on the Rietveld refinement at room temperature. The diffusivity of phase transition and relaxor behavior are both strengthened by the yttrium substitution. The maximal pyroelectric coefficient decreases, and the extent of corresponding temperature deviated from the dielectric peak temperature to higher temperature increases with increasing the yttrium content. The adiabatic temperature changes and isothermal entropy changes display the same tendencies as those of the pyroelectric coefficients. The Ba(Ti0.944Y0.056)O2.972 ceramic shows the largest adiabatic temperature change and largest isothermal entropy change among all compositions over a broad temperature range of 50 K. For individual composition, the value of pyroelectric coefficient decreases with increasing the magnitude of applied electric field, and the temperature of maximal pyroelectric coefficient deviates from the dielectric peak temperature to higher temperature. Therefore, the optimal electrocaloric temperature can be adjusted by the magnitude of electric field in relaxor ferroelectricity.

Improvement in dielectric, piezoelectric and ferroelectric properties of 0.64PMN–0.36PT ceramics by Sb modification

Pure and Sb-doped 0.64PMN–0.36PT (PMN–PT) ceramics near MPB have been prepared using columbite precursor technique. The effects of Sb-doping on microstructure and electrical properties were studied systematically. Powder XRD and SEM exhibited the formation of pure perovskite phase with homogeneous microstructure. As compared to the pure PMN–PT ceramics, enhanced dielectric constant, and reduced transition temperature (Tm) and dielectric loss (tan δ) were observed for Sb-doped PMN–PT ceramics. Displacement–Voltage (D–V) butterfly hysteresis loops and quasi-static d33 meter revealed a higher value of piezoelectric charge coefficient (d33) for Sb-doped sample (644 pm/V and 551 pC/N) as compared to pure ceramic (435 pm/V and 410 pC/N). P–E hysteresis curves showed improved ferroelectric properties after Sb doping. A high value of pyroelectric coefficient (p ∼ −1170.4 µC m−2 °C−1) for Sb-doped PMN–PT ceramic was obtained. Sb-doped PMN–PT ceramic showed an excellent anti-fatigue nature over 107 switching cycles. Small leakage current was evident from J–E analysis for both the ceramics. Therefore, Sb-doped PMN–PT ceramic proved to be a better choice for applications in the electronic ceramic industries.

Field induced phase transitions and energy harvesting performance of (Pb,La)(Zr,Sn,Ti)O3 single crystal

(Pb,La)(Zr,Sn,Ti)O3 (PLZST) single crystals with composition close to the morphotropic phase boundary had been grown by the flux method. The antiferroelectric-ferroelectric phase switching electric field was 0.8 kV/mm. Temperature-dependent dielectric and polarization versus electric field hysteresis loops revealed that the electric field induced ferroelectric phase could transform back into the antiferroelectric phase at depolarization temperature (145 °C). An enhanced pyroelectric coefficient value of 1.46 μC/cm2/K was obtained at 145 °C, which is several times larger than that of conventional pyroelectric materials. Furthermore, multiple peak pyroelectric responses and an enhanced harvested energy density value of 0.4 J/cm3 were achieved in the PLZST crystal. The enhanced harvested energy density and multiple peak pyroelectric responses make the PLZST crystal a promising candidate for high sensitive temperature sensors and energy conversion technologies.

Synthesis of 0.64Pb(Mg1/3Nb2/3)O3–0.36PbTiO3 ceramic near morphotropic phase boundary for high performance piezoelectric, ferroelectric and pyroelectric applications

A near MPB composition of 0.64PMN–0.36PT ceramic has been synthesized by solid-state reaction technique using columbite precursor. Sintering at 1030 °C resulted in a single perovskite phase with tetragonal structure having uniform and dense microstructure as revealed by powder XRD, Raman spectroscopy and FESEM analyses. An excellent dielectric response was obtained with room temperature dielectric permittivity value of 142 and high-phase transition temperature (Tm) of 210 °C at 1 kHz. A huge value of piezoelectric charge coefficient (490 pC/N) was obtained, which shows potential of PMN–PT for piezoelectric device applications. Well-shaped and fatigue-free P–E hysteresis loops over a wide temperature range of 30–230 °C were traced. A very large value of pyroelectric coefficient (p ∼ 2739.2 μC m−2 °C−1) was obtained.

Enhanced AlN nanostructures for pyroelectric sensors

AbstractMeasurements of the pyroelectric coefficient and pyroelectric voltage response of polycrystalline AlN films are presented. The results were used to calculate pyroelectric detectivity figures of merit in order to compare potential AlN pyroelectric sensor performance to other pyroelectric materials such as epitaxial AlN, PbSc0.5Ta0.5O3, and Ba0.65Sr0.35TiO3 films. We observed substantial enhancement (∼5x) of pyroelectric coefficient and pyroelectric figure of merit in polycrystalline multi‐oriented AlN films when compared to epitaxial monocrystalline AlN films. A mechanism of such augmentation in polycrystalline AlN films is proposed and discussed. Despite the relatively small absolute value of pyroelectric coefficient, AlN presents pyroelectric detectivity figure of merit near the same magnitude as commonly used pyroelectric materials because of its relatively low dielectric constant. The low dielectric constant enables high speed sensor operation >MHz. The results of these studies are suggesting even higher pyroelectric response might be obtainable for the polycrystalline thin film AlN structures. (© 2014 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Primary and secondary pyroelectric coefficients of rhombohedral and tetragonal single-domain relaxor-PbTiO3 single crystals

The primary and secondary pyroelectric coefficients were determined for binary (1-x)Pb(Mg1/3Nb2/3)O3–xPbTiO3 (PMN-PT) and ternary Pb(In1/2Nb1/2)O3-Pb(Mg1/3Nb2/3)O3–xPbTiO3 (PIN-PMN-PT) relaxor-PT single crystals. The secondary pyroelectric coefficients were calculated from the thermodynamic inter-relationship between the piezoelectric, elastic, and thermal expansion coefficients. Poling along [111] and [001] directions resulted in single-domain state of “1R” and “1T” and a macroscopic symmetry of 3m and 4mm for rhombohedral (x = 0.28) and tetragonal (x = 0.42) crystals, respectively, enabling relatively large values of pyroelectric coefficients p ≥ 5.7 × 10−4 C/m2 K. The calculated results show that the secondary pyroelectric coefficients are in the range of (−0.62 ∼ −1.06) × 10−4 C/m2 K for rhombohedral crystals and (0.70 ∼ 1.14) × 10−4 C/m2 K for tetragonal crystals, significantly lower than that of primary pyroelectric coefficients, which is important for thermal directional and imaging applications. In contrast, high d15 piezoelectric coefficients (>2000 pC/N), together with zero pyroelectric coefficients in thickness shear crystals, also makes them promising candidates for piezoelectric sensors where thermal noise is undesirable.

Environment friendly novel piezoelectric 0.94[Na0.8K0.2NbO3]–0.06LiNbO3 ternary ceramic for high temperature dielectric and ferroelectric applications

A new composition of lead free piezoelectric ternary ceramic 0.94[Na0.8K0.2NbO3]–0.06LiNbO3 has been synthesized. A well defined and less porous microstructure of the ceramic was prepared by optimized sintering at 1155 °C. High temperature orthorhombic to tetragonal phase transitions at 194 °C and Curie phase transition at 438 °C were observed with real dielectric constant values ∼1400 and 10,500 at 1 kHz, respectively. The NKLN ceramic showed normal ferroelectric behavior. Its ac conductivity followed jump relaxation model for lower frequencies and double power law at higher frequencies with strong temperature dependence. A very high value of the piezoelectric charge coefficient 291 pC N−1 was obtained which implies its potential application in piezoelectric devices. Well switchable square shape and fatigue free P–E loops with high remnant polarizations were obtained in the temperature range 20 °C–100 °C. Pyroelectric coefficient value was found to be −874.3 μC m−2 °C−1 and 560 μC m−2 °C−1 for the temperature range 20 °C–60 °C and 60 °C– 100 °C respectively.

Piezoelectric and pyroelectric properties of Sr-doped PZT (PSZT) with minor manganese additions

A systematic study was performed to see the effect of Manganese addition and temperature gradient on the electrical properties of PSZT. Pb0.96 Sr0.04 (Zr0.52Ti0.48) O3 (PSZT) containing 0.3%, 0.5%, and 1% Mn was prepared by the sol gel method in order to ensure good stoichiometry and enhanced purity. The powders were calcined at 550 °C and sintered at 1200 °C to achieve 98% of the theoretical density. High field ac study was performed by (P-E) hysteresis measurements at different temperatures (RT, 60, 90, 120 and 150 °C) using an electric field up to 3 kV/mm. It was observed that for a lower Mn concentration P-E loops are pinched at the center while this constriction is found to decrease for greater concentrations. The optimized results were obtained for the 1 mol% of Mn content with 4 mol% of Sr. The values of Qm, k, d33 and tanδ were measured as 756, 0.38, 257 and 0.002 respectively. Higher temperatures coupled with a gradual increase of the electric field resulted in a shift of the hysteresis loops along electric field axis, indicating the presence of an internal bias field. Dependence of pyroelectric properties on applied electric field was also investigated. The value of pyroelectric coefficient was found maximum 6.25 × 10−4 (C/m2K) at 3 kV/mm.