Pyroelectric Current Research Articles

Role of delocalized charges in the pyroelectric effect

The temperature dependence of the pyroelectric effect is investigated. An increase in dark conductivity resulting from either trap depopulation or proton migration is shown to suppress the pyroelectric-generated high voltage. Electrically shorting crystal z surfaces coated with a transparent conductive layer is shown to be effective in eliminating the breakdown of the surface charge in air and thus provides a means to study weak thermoluminescence in pyroelectric crystals. In addition, a new method to measure proton migration and dark conductivity is proposed; a direct correlation between the emitted light intensity resulting from ionization of air and the pyroelectric current is observed.

Dielectric and Pyroelectric Properties of Pb[(Fe1/3Sb2/3)xTiyZrz]O3 Ceramics

The temperature dependence of pyroelectric and dielectric properties was measured for polycrystalline Pb[(Fe 1/3 Sb 2/3 ) x Ti y Zr z ]O 3 where x = 0.1, y = 0.4–0.5 and x + y + z = 1 in the temperature range from 300 K to 650 K. The total pyroelectric effect was determined by measuring the pyroelectric current. The changes of dielectric permittivity ϵ′ confirmed the temperature points of the phase transitions occurring in Pb[(Fe 1/3 Sb 2/3 ) x Ti y Zr z ]O 3 . Two diffused phase transitions are observed in the system. The paraelectric-ferroelectric transition near T m is demonstrated by a maximum of dielectric permittivity. The anomaly on ϵ′(T) dependence near 530 K for y = 0.43 speaks for ferroelectric(tetragonal)-ferroelectric(rhombohedral) phase transition. For y > 0.44 this transition is definitely diffuse and the coexistence of tetragonal and rhombohedral phases is observed in a wide temperature range around 530 K. The temperature dependences of the pyroelectric coefficient confirmed the diffuse character of phase transitions in Pb[(Fe 1/3 Sb 2/3 ) x Ti y Zr z ]O 3 .

Pyroelectric and Transient Current Properties of Multilayer Pb1.1(Zr0.3Ti0.7)O3/PbTiO3 and Pb1.1 (Zr0.3Ti0.7)O3 Thin Films

Pb 1.1 (Zr 0.30 Ti 0.70 )O 3 (PZT) and Pb 1.1 (Zr 0.30 Ti 0.70 )O 3 /PbTiO 3 (PZT/PT) multi-layered thin films are grown on Pt/Ti/SiO 2 /Si substrate by sol-gel method. The kinetics of current change of pyroelectric and transient response between PZT and PZT/PT ferroelectric thin films is investigated. The shape of peak in the PZT film is sharp, but that of PZT/PT is broadened. An increase in the peak value of switching current and switching time in the PZT/PT film is observed. The change of pyroelectric and transient current between PZT/PT and PZT films is discussed in terms of internal field.

Aging and slow dynamics inSrxBa1−xNb2O6

The uniaxial ``relaxor'' ferroelectric ${\mathrm{Sr}}_{x}{\mathrm{Ba}}_{1\ensuremath{-}x}{\mathrm{Nb}}_{2}{\mathrm{O}}_{6}$ (SBN) is found to crossover from holelike to cumulative aging as it is cooled into the frozen relaxor regime. The cumulative aging contrasts sharply with the behavior of cubic relaxors, supporting ideas that the spin-glasslike aging in cubic relaxors is connected with polarization components orthogonal to the net ferropolarization. In the relaxor regime, small dc fields are found to suppress much of the dissipative response, similar to long-time aging. Pyroelectric currents are measured, along with limits on pyroelectric noise, allowing limits to be set on dynamically coherent domain sizes. Large nonlinear susceptibilities are found near the freezing transition.

Pyroelectricity and Spontaneous Polarization in [111] Oriented0.955 Pb(Zn1/3Nb2/3)O3–0.045PbTiO3 Single Crystals

We report that the measurements of the pyroelectric current of thepre-poled [111]-oriented0.955 Pb(Zn1/3Nb2/3) O3–0.045 PbTiO3(PZN-4.5%PT) single crystals can shed some light on the phasetransition and spontaneous polarization characters of thismaterial in a similar way to measures of remanent polarization anddielectric properties. The pyroelectric current is measured and thecorresponding spontaneous polarization is calculated as a function oftemperature with various poling fields added during cooling the samplefrom 200 degrees C to room temperature. Critical electric field of0.061 kV/cm is found to be essential to induce the intermediateferroelectric orthorhombic phase between the ferroelectric rhombohedraland tetragonal phases. Below the critical field, the polarizationincreases almost linearly with the increase of poling field. At thecritical field, the polarization at 30 degrees C increases abruptly from14 μC/cm2 for a poling field of 0.06 kV/cm to29.5 μC/cm2 for a poling field of 0.061 kV/cm, andafterwards, increases slowly and saturates to 31 μC/cm2 forpoling fields beyond 0.55 kV/cm.

Electrical properties of Pb2Bi3DyTi5O18 ceramic

Single-phase orthorhombic tungsten bronze (OTB) ceramics, Pb2Bi3DyTi5O18, were prepared by a high-temperature solid-state reaction method. Electrical impedance, phase angle, dielectric constant and dielectric loss were measured in the frequency range 0.1 kHz to 3 MHz at room temperature. The temperature variation of the dielectric constant shows a diffuse phase transition having a diffusivity parameter value of 1.71 at 1 kHz. Pyroelectric current was measured using a direct measurement technique. The temperature dependence of spontaneous polarization was evaluated from the pyroelectric coefficient. The values of the pyroelectric coefficient and spontaneous polarization at room temperature were found, respectively, to be 1.308 × 10–10 C cm–2 °C–1 and 1.993 × 10–7 C cm–2. The activation energy (Ea = 0.516 eV) was estimated from the temperature variation of the dc resistivity. (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Dielectric properties and phase transitions of (Pb 0.87La 0.02Ba 0.1)(Zr 0.6Sn 0.4− xTi x)O 3 ceramics with compositions near AFE/RFE phase boundary

The electrical properties and phase transition behavior of (Pb 0.87La 0.02Ba 0.1)(Zr 0.6Sn 0.4− x Ti x )O 3 solid solutions (PLBZST, 0.04≤ x0.2) were investigated by the X-ray diffraction, permittivity, pyroelectric current, and P– E electric hysterisis loops. As the composition x increased from 0.04 to 0.2, the antiferroelectric ceramics ( x≤0.07, AFE) with tetragonal phase changed to the ferroelectric relaxors (RFE, 0.09≤ x). AFE ceramics showed a peculiar diffuse phase transition and dielectric relaxation at the low temperature (down to −100 °C) due to a frustration between AFE and FE state. With an increase in composition x, electrically field-induced AFE–FE switching field ( E AFE–FE) and AFE–paraelectric (PE) phase transition temperature ( T c) are depressed in the temperature ( T)–Ti composition ( x) phase diagram, a FE–AFE–PE triple phase point ( T tr) with the lowest transition temperature occurred at x=0.09. The pyroelectric currents under an application of various external electric field ( E) were measured to identify a T– E phase diagram of the PLBZST compound.

Chromium-and manganese-doped TlInS2—A new relaxor ferroelectric

The dielectric, pyroelectric, and polarization properties of TlInS2 crystals doped with 0.1 mol % Cr and Mn are investigated. It is shown that TlInS2 compounds doped with chromium and manganese can be assigned to the class of relaxor ferroelectric materials. The temperature range of existence of the stable relaxor (nanodomain) state and the temperature of the phase transition from this state to the ferroelectric (macrodomain) state are determined. The temperature dependence of the pyroelectric current is characterized by an anomaly in the range of the phase transition.

Mapping Surface Polarization in Thin Films of the Ferroelectric Polymer P(VDF-TrFE)

Pyroelectric Scanning Microscopy (PSM) has been developed to enable mapping of surface polarization in ferroelectric thin films, in particular the copolymer polyvinylidene fluoride triflourorethylene, or P(VDF-TrFE). The Chynoweth method for dynamically measuring pyroelectric current is employed in conjunction with a micropositioning system to construct two-dimensional images of the film polarization. These images have revealed an enhancement of the polarization near the edges of the film below the average coercive field, with the center's polarization increasing thereafter to meet the edge value at saturation.

Low Temperature Behaviour of Betaine Phosphate-Betaine Arsenate Mixed Crystals

The mixed system of betaine arsenate and betaine phosphate (BP)x(BA)1−x displays, at low temperatures, dielectric anomalies that have been tentatively associated to re-entrant glass phases. In this work, we report results obtained for the composition x = 0.52. The temperature dependence of the complex dielectric constant, polarization hysteresis loops and pyroelectric currents reported prove that an effective ergodicity breaking occurs in the antiferroelectric phase and show that this phase is destabilized at low temperatures. There is also evidence for a high internal bias field, in the whole temperature range studied. Infrared and Raman spectroscopy indicate that the various dielectric anomalies observed reflect structural transformations.

Thermally Stimulated Current Measurement for Degraded Pb(Ti,Zr)O3 Thin-Film Capacitors

Ferroelectric random access memory (FeRAM) application has suffered seriously from the degradation of ferroelectric thin films such as that caused by fatigue. Therefore, we have investigated the degradation of Pb(Ti,Zr)O3 (PZT) films by thermally stimulated current (TSC) measurement. The TSC has been utilized for the analysis of defects in bulk semiconductor materials. However, TSC evaluation in ferroelectric films has not been studied sufficiently because of the noise current from films and the fluctuation in the calculated trap activation energy. Therefore, we have developed and optimized a modified TSC measurement method that involves a repetition of heating and cooling cycles. Our modified method has enabled the elimination of the noise current due to pyroelectric and leakage currents and the detection of a clear TSC signal from crystalline defects. The activation energy can also be analyzed through the comparison of TSCs for several specimens subjected to various degradation treatments, such as fatigue and the introduction of lead and oxygen defects. Identical trap levels of (I) 0.75 eV and (II) 0.95 eV were observed for these films, and the latter seems to be related to the degradation since the densities of trap (II) increased in all of the degraded films. It is believed that trap (II) is attributed to Pb defects. Therefore, we propose the following degradation mechanism: polarization reversal induces crystalline defects, and the trap level of a Pb site increases with the presence of the defects. The degradation of ferroelectric properties seems to occur because of the existence of the trap.

Pyroelectric Technique for Measurement of Thermal Diffusivity of Thin Solid Materials

A technique for the measurement of the thermal diffusivity of thin samples of solid materials is presented. It is based on the measurement of the phase retardation of a thermal wave passing through the test material. The test material, which can be either ferroelectric or non-ferroelectric, is attached by means of a high thermal conductivity cement to a LiTaO3 pyroelectric detector. A sinusoidally-modulated laser beam impinges on the upper surface of the sample and is absorbed as heat. The heat diffuses in the form of thermal waves through the test sample to the LiTaO3 detector, generating a pyroelectric current. The phase lag between the pyroelectric current and the laser beam intensity is a unique function of the sample thickness and its thermal diffusivity. It is not necessary to know either the pyroelectric coefficient of the detector or the intensity of the laser beam. Thermal diffusivity measurements on LiTaO3, glass and a porous PZT 3-3 composite are presented.

Corona charging and pyroelectric behavior in acrylonitrile-co-methylacrylate films

Annealed and stretched films of P(AN-MA) were charged with negatively constant-voltage corona at different temperatures. Electric field induces phase transition, which is determined by the wide angle X-ray diffraction. Using the thermally stimulated depolarization technique, pyroelectric currents have been investigated in unpolarized and corona charged P(AN-MA) films over the temperature range 25-140C. Stretching films produces an enhancement in pyroelectricity. The increase in crystallinity and the presence of space charge build-up during corona charging are believed to be the chief contributors to the higher pyroelectric activity in the stretched films.

Determination of the polarization distribution in a weakly-poled PVDF film using the surface laser intensity modulation method (SLIMM)

The surface laser intensity modulation method (SLIMM) is used for the determination of the spatial distribution of the polarization normal to and near the surface of a ferroelectric sample. The experimental data measured are pyroelectric currents as functions of frequency. The data analysis requires the solution of a Fredholm integral equation of the first kind. This is an ill-posed problem which has multiple and very different solutions. The experimental method and a technique for data analysis are described. Experimental data on a weakly-poled polyvinylidene fluoride (PVDF) film are presented and the polarization distribution is calculated.

Polarization and space charge analysis in thermally poled PVDF

The spatial distribution of the polarization and space charge in thermally poled poly (vinylidene fluoride) is studied using the laser intensity modulation method. Injected space charge, localized near the electrode polymer interface, tends to prevent the formation of uniform polarization in the polymer bulk. The actual amount of charge existing in the poled specimen is determined using hysteresis measurements and thermally stimulated discharge current (TSDC) measurements. By using the peak cleaning technique and by measuring the pyroelectric current during the cooling of the specimen, the contribution of depolarization current and space charge detrapping to the TSDC measurement is considered. From hysteresis measurements a relaxation process was observed around 65°C which was related to the dipolar relaxation in the crystalline phase known as the αc relaxation. A significant increase of the TSDC at temperatures higher than 130°C was observed meaning that the dipolar charge and the space charge are very stable up to high temperature. In this temperature range, the pyroelectric current is significant. Two relaxation processes were identified for a polarizing temperature lower than 120°C. One is centred around the polarizing temperature and is related to space charge release. The second is related to dipole relaxation in the crystalline phase. The position of the last peak is determined by interaction between the dipoles and the internal electric field, resulting from the charge stored in the sample. We propose to call this as the αcρ interaction. The higher temperature of the dipolar peak was identified as 86°C with an activation energy of 0.52±0.04 eV.

Polarization correlation and pyroelectric properties of Pb(Zr, Ti)O3 and La doped Pb(Zr, Ti)O3 multilayer thin films

Polarization correlation was found in the alternatively deposited Pb(Zr, Ti)O3 (PZT 30/70) and La doped Pb(Zr, Ti)O3 (PLZT 17/30/70) multilayered thin films prepared by a modified sol-gel process. HRTEM results revealed that the multilayered thin films had their (111)-pre-ferred orientation and crystalline size of 300 nm. Dielectric constants and losses at 1 kHz for the un-poled sample and the sample poled at 357 kV/cm were 880, 800, and 0.022, 0.019 respectively. A high pyroelectric current was observed in the PZT/PLZT multilayered thin film near the PLZT phase transition point even after several thermal cycles above the phase transition temperature of the PLZT layer. This phenomenon was termed as the self-biased dielectric bolometer (SBDB) effect, and was attributed to the induced polarization in PLZT layers by the remnant polarization in their adjacent PZT layers.

Pyroelectric characteristics of thin PbTiO3 and la-modified PbTiO3 films on platinum films for infrared sensors

In this work, we grew lead titanate (PbTiO3) and La-modified PbTiO3 thin films on platinized silicon (Si(100)) substrates under controlled substrate temperature and ambient by a modified jet-vapor deposition (JVD) process described in this paper. The x-ray diffraction patterns obtained from these films showed a single-phase perovskite structure. We examined locally homogeneity and thickness of these films through the comparative use of laser Raman spectroscopy. We also collected Raman and x-ray data on pure PbTiO3, as well as prepared lead zirconate titanate (PZT) (54/46), and PZT (50/50) films using the JVD process. This paper discusses the temperature variations of the pyroelectric and dielectric properties of three compositions of La-modified PbTiO3 films containing 5.2% to 15% of La, respectively, with a view toward studying the effect of La in place of Pb on these electrical properties. We detected significant pyroelectric currents on all three La-modified PbTiO3 films before performing poling treatments, and observed pyroelectric coefficeints as high as 84 nC/cm2·°C in the poled La-doped PbTiO3 films containing 5.2% La. The pyroelectric coefficient and dielectric constant varied significantly with La content. We compared the calculated figures of merit, which were based on the measured physical properties, with pure PbTiO3 as well as PZT and lead lanthanide zirconate titanate (PLZT) films. These properties just described illustrate that these films would be suitable for IR detectors.

Corona charging and pyroelectric behaviour in acrylonitrile-co-methylacrylate films

Annealed and stretched films of P(AN-MA) were charged with negatively constant voltage corona at different temperatures. Electric fields induce a phase transition which is determined by wide angle X-ray diffraction. Using the thermally stimulated depolarisation technique, pyroelectric currents have been investigated in unpolarised and corona charged P(AN-MA) films over the temperature range 25–140°C. Stretching films produces an enhancement in pyroelectricity. The increase in crystallinity and the presence of space charge build-up during corona charging are believed to be the chief contributors to the higher pyroelectric activity in the stretched films.

Self-biased dielectric bolometer from epitaxially grown Pb(Zr,Ti)O3 and lanthanum-doped Pb(Zr,Ti)O3 multilayered thin films

A self-biased dielectric bolometer has been realized by epitaxially grown lead zirconate titanate Pb1.1(Zr0.3Ti0.7)O3 (PZT 30/70) and lanthanum-doped lead zirconate titanate Pb0.83La0.17(Zr0.3Ti0.7)0.9575O3 (PLZT 17/30/70) multilayered thin films using the sol-gel technique. The high-resolution transmission electron microscopy images and electron diffraction pattern showed that the multilayered film had its preferred (111) orientation and the epitaxial growth between the PZT 30/70 and PLZT 17/30/70 layers. The self-biased phenomenon and a large pyroelectric current were observed in the prepoled sample without any external bias at the PLZT 17/30/70 phase transition temperature of 120 °C. Pyroelectric coefficient as high as 990 μC/m2K is obtained in the multilayer thin films around 120 °C. It is obvious that there exists an induced polarization in the PLZT 17/30/70 layer. We attribute this self-biased effect to the strong remnant polarization in the immediately contacted tetragonal PZT 30/70 layers.

Corona-charged thin films composed from antiferroelectric solid mixtures of achiral side-chain liquid crystalline polymers and their monomers

The results of investigations on corona charged thin mesogenic films consisting of solid mixtures of achiral liquid crystalline side-chain polymers and their monomers are presented. A pyroelectric modulation and a low frequency piezoelectric technique were used to confirm the polar properties of these compounds. The pyroelectric coefficient γ and the apparent longitudinal piezoelectric coefficient d33 were measured in the glassy state to be 3.2 nC/cm2K and 9 pC/N. The pyroelectric currents versus modulation frequency for various polar materials were studied for comparison.