Showing papers on "Pyroelectricity published in 1993"

Electron emission from ferroelectric materials

Abstract: Ferroelectric materials are a new class of electron emitters. Electron emission occurs due to the appearance of an unscreened charge and an electrostatic field at the polar surfaces of these crystals under pyroelectric, piezoelectric, and anomalous photovoltaic effects as well as during spontaneous polarization reversal. Small external perturbation (for example, a temperature variation of a few degrees or less) is enough for this emission effect to occur. Emission current density up to 103 A cm−2 and electron energy up to about 105 eV have been reported. It is shown that this phenomenon drastically differs from other kinds of electron emissions. The physical nature of this effect is discussed.

Exact Results in the Micromechanics of Fibrous Piezoelectric Composites Exhibiting Pyroelectricity

Abstract: Piezoelectric fibrous composites of two, three and four phases are considered. The phase boundaries are cylindrical but otherwise the microgeometry is totally arbitrary. The constituents are transversely isotropic, and exhibit pyroelectricity. Exact relations are derived between the local fields arising under a uniform electromechanical loading and a uniform temperature change in the piezoelectric composite. For given overall material symmetry, exact connections are obtained among the effective elastic, piezoelectric and dielectric constants of two- and three- phase systems. It is also shown that the effective thermal stress and pyroelectric coefficients can be expressed in terms of the effective elastic, piezoelectric, dielectric constants and constituent properties in two-, three- and four-phase composites.

Dielectric, pyroelectric, and thermally stimulated depolarization current investigations on lead‐lanthanum zirconate‐titanate‐x/95/5 ceramics with La content x=0.5%–4%

Abstract: It is shown that La dopants have a strong influence on the antiferroelectric‐ ferroelectric‐paraelectric (AFE‐FE‐PE) phase transitions and properties of the lead‐lanthanum zirconate‐titanate‐x/95/5 ceramics (with La contents x=0.5%–4%). The occurrence of the ferroelectric microdomains, dispersed in the AFE and PE matrices, gives rise to properties typical for ferroelectric relaxors. The space‐charge concentration polarization, formed by some mobile ion defects, plays an important role in this behavior. This space‐charge polarization and its interaction with the spontaneous polarization was investigated by dielectric, pyroelectric, and thermally stimulated depolarization current measurements. A qualitative model of interpretation is discussed.

Structure and properties of ferroelectric copolymers of poly(vinylidene fluoride)

Abstract: The aim of this paper is to review the main structural features and properties which are related to the ferroelectric behavior of copolymers of poly(vinylidene fluoride) (PVF2). These are illustrated by describing the conformation, polymorphism and morphology of PVF2 and its copolymers. Copolymers of PVF2 and trifluoroethylene have special interest because of their prominent ferroelectric behavior as well as strong piezo- and pyroelectric activity. The review covers the study of the influence of molar composition on structure and the temperature induced ferroelectric to paraelectric phase changes. Advances and problems in X-ray diffraction results relating to changes in the long period, size of coherently diffracting domains and lattice spacings with temperature are discussed. A microstructural model to explain the transformation of paraelectric into ferroelectric crystals when cooling through the transition temperature is presented. Special attention is paid to the influence which the changes in structure exert upon mechanical properties. The dependence of polarization upon copolymer composition and temperature is analyzed. Dielectric spectroscopy is shown to be of great interest in showing transitions connected with reorientation of permanent dipoles. Finally, new results on molecular dynamics of these ferroelectric copolymers derived from incoherent neutron scattering are reported.

Dependence of Piezoelectric and Pyroelectric Activities of Aromatic Polyurea Thin Films on Monomer Composition Ratio

Abstract: Thin films of aromatic polyurea were prepared by simultaneous deposition of 4,4'-diamino diphenylmethane (MDA) and 4,4'-diphenylmethane diisocyanate (MDI) on a polyimide film substrate. By changing the evaporation temperature of the monomers, the monomer molar ratio of MDA to MDI of the deposited film was varied to yield MDA-rich, balanced, and MDI-rich films. After poling, the balanced films exhibited the maximum values of pyroelectric and piezoelectric constants, which were stable up to 200°C. Elemental analysis confirmed that oligomers consisting of about five monomers were present in as-deposited films. In the balanced films, an exothermic peak appeared at about 110°C in the first run of DSC measurements and the IR absorption peak due to isocyanate groups disappeared after heat treatment. These results suggest that during the poling process polymerization of oligomers, which forms polar urea bonds, takes place at about 110°C under a high electric field. The large residual polarization thus produced leads to high pyroelectric and piezoelectric activities.

Measurement of the pyroelectric coefficient in composites using a temperature-modulated excitation

Abstract: Ferroelectric polymers such as PVDF and its copolymer P(VDF/TrFE) as well as ferroelectric ceramic-polymer composites have to be annealed at a high temperature for an extended period of time after polling, before the measurement of the pyroelectric coefficient by the direct method can be performed, in order to eliminate the high depolarization current which hinders the determination of the true pyroelectric current. Here it is suggested that a periodic temperature oscillation of a ceramic-polymer composite sample would permit measurement of its true pyroelectric coefficient without the need to anneal the sample. The temperature distribution inside the composite sample, the magnitude of the pyroelectric current and their variation with the frequency of temperature oscillation have been simulated with the present theory. Pyroelectric measurements using this technique have been made on a poled composite of calcium-modified lead titanate (PbTiO3) and a copolymer of vinylidene fluoride and trifluoroethylene P(VDF/TrFE) and compared with the results of the direct measurements before and after annealing, in order to test the validity of the method.

Antipolarity domain nucleation and growth during heat treatment of proton‐exchanged LiTaO3

Abstract: Ferroelectric local domain inversion occurs in LiTaO3 crystals by proton exchange followed by heat treatment at temperatures just below the Curie point, thereby yielding an inversion layer at the −c surface. This article reports the domain inversion phenomenon in LiTaO3 plates and the experiments performed to clarify the mechanism. Measurements of dielectric constant and electrical conductivity near the Curie temperature suggest that the pyroelectric fields induced during the cooling down period are not likely to be the main cause of the domain inversion. This experimental result is reinforced by measurements of the piezoelectric response during heat treatment, which shows that the antipolarity domain nucleates at the initial stage of heat treatment and grows gradually.

Hysteresis measurements on ferroelectric composites

Abstract: Ceramic/polymer composites made of calcium‐modified lead titanate grains in the matrix of a copolymer of vinylidene fluoride and trifluorethylene, in a 65:35 volume fraction percentage, respectively, were produced in order to obtain mechanically strong ferroelectric films with improved piezo‐ and pyroelectric properties. Their poling behavior was studied using a modified ferroelectric hysteresis measurement setup that allowed for the measurement of the remanent polarization Pr and coercive field Ec, as a function of the peak of the sinusoidal applied field, the frequency of the excitation, and the poling temperature. The ranges of variation of the electric field, frequency, and temperature were from 5 to 25 MV/m, from 0.04 to 2 Hz, and from 50 to 120 °C, respectively. Estimates of the activation field and saturation polarization were calculated based on these measurements. The observed properties in the ferroelectric composites were then compared and correlated with the properties of the ceramic material.

Pyroelectric properties of ferroelectric‐polymer composite

Abstract: General formulae of the pyroelectric coefficient and the figure of merit (p/e) of a ferroelectric‐polymer composite are theoretically derived in terms of the volume fraction q, the depolarization coefficient nx, the dielectric constant of the ferroelectric particles and the dielectric constant of the composite. The value of p/e can be expected to be larger than that of pure ferroelectric ceramics. Good agreement is obtained between theoretical and experimental results.

Piezoelectric thin film element

Abstract: PURPOSE: To improve piezoelectric characteristic, ferrodielectric characteristic and pyroelectric characteristic by using a PZT thin film having optimum crystal line orientation property and composition. CONSTITUTION: A titanate zirconate (PZT) film 105 whose chemical formula is Pb 1+y (ZrXTi 1- X)O 3+ Y, composition rate is in the range of O≤X≤0.55 and 0≤Y≤0.5 and crystal structure is rhombohedron system is formed on a substrate 101 wherein a orientation metallic film 104 is formed. A orientation degree of the PZT film 105 to a main surface vertical direction of the substrate 101 is 70% or more. Otherwise, a PZT film 105 whose chemical formula is Pb 1+ Y(ZrXTi 1- X)O 3+ Y, composition rate is in the range of 0.55≤X≤1 and 0≤Y≤0.5 and crystal structure is tetragonal system is orientated on the substrate 101 wherein the orientation metallic film 104 is formed. A orientation degree of the PZT film 105 to a main surface vertical direction of the substrate 101 is 70% or more. COPYRIGHT: (C)1994,JPO

Sputtering of Lead-Based Ferroelectrics

Abstract: PbTiO3(PT), Pb1−xLaxTi1−x/4O3(PLT) and PbZrxTi1−xO3(PZT) thin films were prepared by rf magnetron sputtering. It was found that the thin films have remarkably large pyroelectric effect and high figures of merit for infrared sensors without poling treatment. High performance pyroelectric infrared sensors (single element and linear array) were fabricated by using the PLT(x=0.1) thin films with the new structures and the device process. This type of sensor is carried on the air conditioner to detect a thermal environment. The PZT thin films with x=0.9 showed a large remanent polarization of 46μC/cm3 and small coercive force of 28kV/cm. In addition, good endurance behavior (no degradation of Pr after 1011 cycles) was observed. Recent activities of ferroelectric thin film research in Japan is also reported.

Electric and pyroelectric behaviors of PbTiO3 thin films formed by an excimer laser ablation technique

Abstract: Ferroelectric PbTiO3 thin films have been formed on base electrodes of platinum by an ArF excimer laser ablation technique. X-ray diffraction patterns of the films show c-axis orientation with a rocking angle of 0.8°-0.5° under the cooling rate conditions of less than -75°C/min. These films exhibit ferroelectric hysteresis loops. The PbTiO3 film, formed at 550°C in O2 pressure of 100 mTorr, has a dielectric constant, coercive field and remnant polarization of 130, 280 kV/cm and 80 µC/cm2, respectively. These values are too large but they are rather similar to the values of theoretical data. Voltage responsivities of these films are 1000-1500 V/W at the frequency of 10 Hz even without poling treatment.

Study of modified tgs crystals

Abstract: Based on the relation between the structure and spontaneous polarization of TGS crystal, some modified TGS crystals have been grown by doping with aniline-family dipolar moleculars, inorganic acids and metal ions in the crystals. The effects of different dopants on growth habit and pyroelectric properties were investigated. The experimental results show that the pyroelectric figure of merit (p/e) of these new modified TGS-ATGSP and ATGSAs are one time higher than that of pure TGS crystal. The main approach of study on the modification of TGS crystal is also discussed in this paper.

Thermal stability of internal electric field and polarization distribution in blend of polyvinylidene fluoride and polymethylmethacrylate

Abstract: It is confirmed that a melt‐quenched and annealed blend of 80 wt % polyvinylidene fluoride and 20 wt % polymethylmethacrylate has the β‐crystal form of PVDF with optical clarity and other properties that are desirable for a host material in a guest‐host system where the guest is an optically nonlinear dye that is orientationally stabilized by the strong internal electric field of a poled ferroelectric. Combined measurements, in such a blend, of the internal electric field Ei, the pyroelectric coefficient Cpyro, and the polarization distribution after electrically poling and subsequently thermally aging for 2 h intervals at temperatures up to 120 °C are reported. Ei and Cpyro increase with increasing poling field Ep. Ei was found to be as large as three times Ep. An unexpected thermal stability of Ei was observed at annealing temperatures above the glass transition temperature of 60 °C up to 100 °C when significant loss of Cpyro was measured. Thermal pulse results yield polarization distributions that may ...

Modified triglycine sulphate for pyroelectric infrared detectors

Abstract: Doped single crystals of the TGS family show very good pyroelectric and dielectric properties, which enable them to be applied in pyroelectric detectors. Single domain deuterated and 1-α-alanine doped TGS crystals (DTGS:L-A) and TGS crystals doped with a l-α-alanine/Cr3+ complex (TGS:L-A + Cr3+) were grown. By deuteration Curie temperature can be increased up to 61°C. To improve homogeneity of alanine incorporation and so the uniformity of the internal bias field, the DTGS:L-A crystals were grown at {001} plate seeds10 by the so called box method. TGS:L-A + Cr3+ have extremely high bias fields of more than 50 kV/cm. Thus a high pyroelectric effect is measured even at 100°C. As a result of extensive investigations low dielectric losses of about 2. 10-4… 1.10-3 at a frequency of 103 cps could be achieved with the doped modifications. Finally, the pyroelectric chips of single element, linear and two-dimensional arrays were described and the measured detector properties were summarised.

Piezoelectric material comprising a polymer network

Abstract: The invention relates to a piezoelectric element comprising a piezoelectric material 1, in the form of a polymer network, between at least two electrodes 2, 3. The piezoelectric material is formed from a starring material comprising a liquid crystalline monomeric material and a chiral compound. The starting material is brought to a temperature at which a smectic phase is formed, and an electric field is applied to obtain a dipolar orientation in the starting material, after which the polymer network is formed by means of photopolymerisation. The piezoelectric element thus manufactured can suitably be used for various electromechanical applications, as a sensor material, for pyroelectric applications and, in particular, also for optical applications.

Dielectric and pyroelectric properties of (CH3NH3)3Bi2Br9 crystals in the ferroelectric phase transition region

Abstract: Dielectric and pyroelectric properties of isomorphous crystals (CH3NH3)3Me2Br9 (Me = Sb, Bi) in the low temperature region have been compared. The observed dielectric dispersion in the vicinity of ferroelectric phase transition of both crystals revealed the complex nature. The ferroelastic domain structure in all low temperature phases of these two salts exhibits considerable similarity.

Ferroelectric domain switching in heat-treated LiNbO3 crystals

Abstract: The pyroelectric effect and domain structure of heat-treated (Li2O outdiffused) LiNbO3 crystals have been studied. The heat treatment causes a domain inversion and almost total suppression of the pyroelectric current. Non-inverted domains have been observed in the outdiffused inverted layer. Based on the pyroelectric current-temperature dependence it is suggested that these domains are switched by an intrinsic bulk pyroelectric field.

Thin dielectric film and manufacture thereof

Abstract: PURPOSE: To realize a thin dielectric film damaging no electrical characteristic such as ferroelectricity, pyroelectricity, piezoelectricity, etc., by forming a perovskite type thin dielectric film containing no Zr and a perovskite type thin dielectric film containing Zr in laminated structure. CONSTITUTION: Pb, La and Ti targets 8, 9 and 11 are irradiated with argon ion beams respectively, and a PLT layer 2 in film thickness of 50Å or less having the composition of (Pb 1-x La x )Ti 1-x/4 O 3 (0≤x≤1) is formed onto a substrate 1. Pb, Zr and Ti targets 8, 10 and 11 are sputtered by ion beams, and a PLZT thin-film 3 in film thickness of approximately 700Å having the composition of (Pb 1-x La x )(Zr y Ti 1-y ) 1-x/4 /O 3 (0≤x≤1, 0

Ferroelectric and nonlinear optical properties of ferroelectric-superionic KTP

Abstract: Pyroelectric and nonlinear optical properties of KTP crystals are discussed. The SHG, optical and pyroelectric characteristics of multidomain crystals before and after poling are described and compared to single domain crystals.

Dielectric and pyroelectric properties of [N(CH3)3H]3Sb2Cl9 in the low temperature region

Abstract: Low frequency dielectric investigations of disordered trimethylammonium cations are presented and discussed. Ordering process of N(CH3)3H+ cations are described by means of an asymmetry of doubleminimum potential. Pyroelectric experiment on TMACA provided clear evidence of another continuous phase transition at 127 K between two ferroelectric phases connected most probably with a motion of CH3 groups.

Polyvinylidene fluoride (PVDF) elastic, piezoelectric, pyroelectric, and dielectric coefficients and their non-linearities

Abstract: This work presents a set of material coefficients for a uniaxially 4x stretched 25 μm thick PVDF film. Calculations of the type d = se, where d and e are piezoelectric coefficients and s is the compliance, are used to compare independent measurements of piezoelectric coefficients. The piezoelectric coefficient e333 is found to be constant to strains over 25%. The non-linearities in the dijk coefficients are due to non-linearities in the elastic moduli that are typical of polymers above their glass transition temperature, i.e. strain rate dependent, viscoelastic, temperature dependent.

Pyroelectric Properties of Lead Based Ferroelectric thin Films

Abstract: Lead based thin ferroelectric films have been prepared using both sol-gel and dual ion beam sputtering (DIBS) processes. Material compositions within the PbTiO3 and PLZT system have been deposited by both techniques onto metallised silicon. By using a standard sol-gel prepared solution, modified with acetylacetone and spin-coating, lµm thick fully perovskite layers, were obtained at low temperature (450°C) with some preferred orientation. The grain size was in the range 0.2-0.4µm. A dielectric constant of 400 and a reversible pyroelectric coefficient of 1.2 x 10−4Cm−2K−1 were obtained. In contrast, a range of capping layers (SiO2, A12O3, BPSG) on silicon have been investigated using the DIBS process. Highly crystalline (100) and (111) films were readily produced at temperatures in excess of 550°C, at a growth rate of 0.3µm/hour. Control of stoichiometry has also been studied in detail, by sputtering of a composite metal-ceramic target with a high energy Kr beam and by bombarding the growing film with a low energy oxygen ion-beam. Dielectric constants of 200–300, losses below 0.015 and resistivities above 1010Ωm have been achieved. A pyroelectric coefficient of the order of 2.5 x 10−4Cm−2K−1, pre-poled for a La-doped film on BPSG capped Si was obtained, which did not increase significantly on poling.

Equations of state including the thermal domain of piezoelectric and pyroelectric heterogeneous bimorphs

Abstract: The equations of state for piezoelectric bimorphs made of a piezoelectric and a non-piezoelectric material have been determined. As these bimorphs are nonsymmetric they suffer from considerable temperature sensitivity due to the difference in thermal expansion coefficients of the constituting materials. The deflection, rotation, volume displacement, charge on the electrodes and the entropy change have been calculated for the heterogeneous bimorph.

Theory of electrical properties of molecular crystal surfaces

Abstract: Crystals inevitably have surfaces, near which crystal properties inevitably change. Quantitative changes in magnitude occur because of the loss of interactions near the surface, and qualitative changes in symmetry occur because of the loss of symmetry across the surface. This paper discusses the theory of some surface electrical properties of molecular crystals. All the properties depend on dipolar interactions between the molecules. The interactions are conveniently summed over planes of molecules parallel to the surface, when it is found that interactions between neighbouring planes are generally negligible. This result facilitates computation of surface properties. Applications discussed include surface electric fields, polarization and pyroelectricity, charge-carrier energetics, and nonlinear optics.