Showing papers on "Pyroelectricity published in 1977"
TL;DR: The development and current state of knowledge of ferroelectric liquid crystals are reviewed in this paper, where the Curie point and effects visible in freely suspended films are compared with crystalline ferroelectrics.
Abstract: The development and the current state of knowledge of ferroelectric liquid crystals are reviewed. Symmetry considerations first indicated that a ferroelectric phase should exist. Synthesis of new molecules led to the first experiments on electro-optical properties, indicating a spontaneous polarization. Various studies of bulk samples, including further electro-optical effects, shear induced polarization, pyroelectric effects, and switching experiments are discussed. Studies of the Curie point and effects visible in freely suspended films are summarized. Comparisons with crystalline ferroelectrics are made. Some further work and possible applications are indicated.
361 citations
TL;DR: In this article, a simple theoretical model for amorphous ferroelectricity and interfacial polarization due to localized ionic motion was proposed to explain the dielectric anomalies of LiNbO3 and LiTaO3.
Abstract: Vitreous LiNbO3 and LiTaO3 have been prepared by roller quenching these compositions from the melt. The transparent glasses exhibit pronounced dielectric anomalies with peaks of e≳105 close to the crystallization temperature which are not characteristic of the crystalline phase. Pyroelectricity is induced after cooling the glass in an electric field. The data are discussed in terms of a simple theoretical model for amorphous ferroelectricity and interfacial polarization due to localized ionic motion.
144 citations
TL;DR: The piezoelectric constant of a uniaxially stretched and polarized poly(vinylidene fluoride) film decreases monotonically with increasing temperature in the range from 65 to 165°C.
Abstract: The piezoelectric constant of a uniaxially stretched and polarized poly(vinylidene fluoride) film decreases monotonically with increasing temperature in the range from 65 to 165 °C. After a specimen is cooled under open‐circuit conditions, the thermally stimulated current reverses in sign and exhibits a peak at around the glass‐transition temperature Tg. Reversible changes in infrared spectra before and after the poling process suggest that the dipoles in the β crystals of poly(vinylidene fluoride) can be aligned along the direction of an applied electric field. The alignment is strongly influenced by the amorphous region; the coercive field in P‐E hysteresis curve observed at 50 Hz increases rapidly at around Tg. Under a high electric field, the uniaxially stretched poly(vinylidene fluoride) film behaves above Tg in the same way as ferroelectric ceramics.
92 citations
TL;DR: The ferroelectric Curie temperature, Tc = 1383 K, has been determined from dielectric, thermal and pyroelectric studies as discussed by the authors, and large transparent crystals have been grown by Czochralski pulling.
Abstract: Ferroelectricity has been discovered in calcium vanadate. Large, transparent crystals have been grown by Czochralski pulling. Electrical 180° domains of millimeter dimensions are observed by etching as-grown crystals. The ferroelectric Curie temperature, Tc = 1383 K, has been determined from dielectric, thermal and pyroelectric studies.
69 citations
TL;DR: The spontaneous polarization of single-domain orthorhombic KNbO3 has been measured with the Camlibel pulse method in this article, and a new value of Ps=0.41±0.02 C/m2, which is about 30% larger than the result obtained in hysteresis measurements, has been observed.
Abstract: The spontaneous polarization Ps of single‐domain orthorhombic KNbO3 has been measured with the Camlibel pulse method. A new value of Ps=0.41±0.02 C/m2, which is about 30% larger than the result obtained in hysteresis measurements, has been observed. The temperature dependence of the pyroelectric coeffficient has been measured using a direct method. The temperature dependence of the spontaneous polarization calculated from these measurements is compared with the results of a Devonshire free‐energy expansion.
50 citations
TL;DR: In this paper, the dielectric properties of a single crystal (NH 4 ) 3 H(SeO 4 ) 2 were measured below room temperature and two phase transitions were found at around +2°C and at -92°C.
Abstract: Dielectric properties of single crystal (NH 4 ) 3 H(SeO 4 ) 2 were measured below room temperature Two phase transitions were found at around +2°C and at -92°C A λ-type peak of the dielectric constant along the c -direction is found at -92°C, and the crystal shows ferroelectricity below the transition The temperature dependence of the spontaneous polarization was measured by a pyroelectric method The Curie temperature linearly increases with increasing hydrostatic pressure up to 85 kbar with a slope of 23 deg kbar -1
47 citations
TL;DR: In this article, preliminary pyroelectric and piezoelectric results obtained with commercial films of nylon 11 were presented, and the results of dielectric-constant measurements in the temperature range 20−130°C were also presented.
Abstract: This paper describes preliminary pyroelectric and piezoelectric results obtained with commercial films of nylon 11. The results of dielectric‐constant measurements in the temperature range 20–130 °C are also presented. Nylon 11 films show quite high pyroelectricity and the evidence indicates that there is probably dipole orientation in crystalline regions. Charge injection or volume polarization, as well as dipole orientation, was shown to contribute to the pyroelectricity unless the sample was thoroughly relaxed.
46 citations
TL;DR: In this paper, Boguslawski's model was tested by refining the structure, at 193 and 293 K, on a sphere of gem-quality elbaite, and it was shown that the pyroelectric effect is due primarily to the asymmetric anharmonic vibrations of O(1), the oxygen atom of point symmetry 3m which has a polar environment.
Abstract: Pyroelectricity in tourmaline, known since antiquity, was ascribed by S. von Boguslawski to a charged, asymmetric, anharmonic oscillator based on the Einstein model of a crystal. His predicted values of the pyroelectric coefficient k were in good agreement with Ackermann's measurements in the range 20-400 K. We have tested Boguslawski's model by refining the structure, at 193 and 293 K, on a sphere of gem-quality elbaite. The pyroelectric effect is due primarily to the asymmetric anharmonic vibrations of O(1), the oxygen atom of point symmetry 3m which has a polar environment. Its centre of gravity moves 0.005 A from 193 to 293 K. It is the only atom with a displacement well above experimental uncertainty. Its large thermal parameters, which are ten times their standard deviation at both temperatures, clearly invalidate the assumption of an ellipsoidal thermal movement. This probably holds for Na and 0(2), which also have abnormally large temperature factors, but show no significant displacement.
34 citations
TL;DR: In this article, it was concluded that a Richardson-Schottky process is dominant at the high fields and temperatures typically employed in poling poly(vinylidene fluoride) to impart pyroelectric and piezoelectric properties.
Abstract: By analysis of steady‐state current‐time‐voltage‐temperature relationships, it is concluded that a Richardson‐Schottky process is dominant at the high fields and temperatures typically employed in poling poly(vinylidene fluoride) to impart pyroelectric and piezoelectric properties. Data on pyroelectric behavior with different layer configurations and with different electrode configurations indicate the primary importance of hole injection.
29 citations
13 citations
TL;DR: In this paper, the 9° tetragonal deformation of the TiO 6 octahedron in PbTiO 3 is monitored as a function of temperature by employing a three-dimensional bond polarizability model to analyze the temperature dependence of optical second harmonic generation.
TL;DR: Quantitative pyroelectric measurements were made on the leaves of the palmlike plant Encephalartos, offering a means for highly increasing the efficiency of conversion of thermal to electrical energy.
Abstract: Quantitative pyroelectric measurements were made on the leaves of the palmlike plant Encephalartos. A pyroelectric response almost 50 times higher than the normal one could be induced by a small bias electric field, offering a means for highly increasing the efficiency of conversion of thermal to electrical energy. No evidence of ferroelectricity was found.
TL;DR: In this article, it was shown that in alanine doped TGS, the pyroelectric coefficient is slightly higher and the dielectric constant and the loss are slightly lower than for pure TGS.
Abstract: Publisher Summary The most sensitive pyroelectric detectors still use what is essentially TGS (triglycine sulfate) However one of the disadvantages of the earlier TGS detectors was that if heated above the Curie point, the material became depoled Although the detector was not permanently damaged, the necessity to repole the detector could be a considerable nuisance This fault is attributed not only to pure TGS, but also to a greater or lesser extent to any ferroelectric with a Curie temperature close to ambient These materials have the most attractive pyroelectric properties, but they must be used with care because of this problem It is also found that in alanine doped TGS, the pyroelectric coefficient is slightly higher and the dielectric constant and the dielectric loss are slightly lower than for pure TGS Thus the performance of detectors made from this material is somewhat better than those made from pure TGS
05 Jul 1977
TL;DR: In this paper, the theory of pyroelectric radiation detectors has been studied in the context of Ferroelectric thermal radiation detectors, and equipment and procedures for determining the characteristics of material and parameters of the detectors have been described.
Abstract: : Contents: Thermal Radiation Detectors; Bases of Physics of Ferroelectric Materials; Pyroelectric Coefficient and Dielectric Constant of Ferroelectric Materials; The Theory of Pyroelectric Radiation Detectors; Pyroelectric Radiation Detectors; Ferroelectric Bolometers; Equipment and Procedures for Determining the Characteristics of Material and Parameters of Ferroelectric Radiation Detectors; Limited Applications of Ferroelectric Thermal Radiation Detectors.
TL;DR: In this paper, a method to study domain structure in ferroelectrics using pyroelectric effect is described, where a triglycine sulphate crystal plate has been studied by scanning the surface of the crystal with a low wattage He-Ne laser beam.
Abstract: A method to study domain structure in ferroelectrics, using pyroelectric effect is described. Variation of pyroelectric signal from the surface of a triglycine sulphate crystal plate has been studied by scanning the surface of the crystal with a low wattage He-Ne laser beam. The integrated pyroelectric signal is due to two components, namely, (1) the primary component arising out of the change in spontaneous polarization with temperature and (2) the delayed component arising out of the possible polarization reversal. The component of an electric field along the ferroelectric axis due to thermal hemisphere within the crystal plate formed by the laser beam has been calculated and shown to exceed coercive field, making polarization reversal possible. The delayed pyroelectric signal is a measure of polarization reversal within the patch illuminated and its observed variation over the surface yields information of the domain structure.
TL;DR: In this paper, a single crystal Pb2.07K0.56Nb0.91Ta4.15O15 has been grown by the flux method and crystallized with the tetragonal tungsten bronze structure.
Abstract: A single crystal Pb2.07K0.56Nb0.91Ta4.15O15 has been grown by the flux method. It crystallizes with the tetragonal tungsten bronze structure. Two transitions have been determined by dielectric, pyroelectric and birefringence measurements: ferroelastic-ferroelectric phase →371 K ferroelastic-paraelectric phase →658 K paraelastic-paraelectric phase. Spontaneous polarization and spontaneous strain are respectively equal to 29 μC · cm-2 and 8 × 10-4 at room temperature. Polar axis is along the [010] direction. Electrical switching of the ferroelastic domains at room temperature shows clearly the existence of a ferroelastic-ferroelectric coupling.
Patent•
19 May 1977
TL;DR: A leaf of suitable dielectrical material bears, trapped on one at least of its two surfaces, equal or substantially equal amounts of positive and negative electrostatic charges, these charges being preferably injected into the leaf by successive ionization in reverse directions of gaseous layers against said surface.
Abstract: A leaf of suitable dielectrical material bears, trapped on one at least of its two surfaces, equal or substantially equal amounts of positive and negative electrostatic charges, these charges being preferably injected into the leaf by successive ionization in reverse directions of gaseous layers against said surface. The device is valuable in piezoelectric or pyroelectric devices such as ultrasonic transducers, pressure or vibration detectors, microphones, heat or infrared radiation detectors.
TL;DR: In this paper, the contact potential difference (CPD) between CdS and Au and the open circuit voltage (OCV) in the direction of c-axis were measured simultaneously on photoconductive insulating cdS crystals with a polar surface and it was concluded that large changes in CPD produced in response to changes in the pressure of the environment in the dark are due to the piezoelectric effect of the crystals.
Abstract: The contact potential difference (CPD) between CdS and Au and the open circuit voltage (OCV) in the direction of c-axis were measured simultaneously on photoconductive insulating CdS crystals with a polar surface. As a result, it was concluded that large changes in CPD produced in response to changes in the pressure of the environment in the dark are due to the piezoelectric effect of the crystals. The changes in CPD produced by changes in temperature from 90 K to 400 K in the dark were also measured on the same crystals and such changes could be accounted for by the generation of pyroelectricity. Moreover, the pyroelectric characteristics were found to show good correspondence to the results of the measurement of the thermally stimulated current in a previous paper.
01 Dec 1977
TL;DR: In this paper, a plasma poling device is described which allows essentially instantaneous poling of polymeric films at room temperature at very high fields using poly(vinylidene fluoride) both undrawn and biaxially drawn (both alpha and beta conformation).
Abstract: : A plasma poling device is described which allows essentially instantaneous poling of polymeric films at room temperature at very high fields Using poly(vinylidene fluoride) both undrawn (comprising essentially pure alpha conformation) and biaxially drawn (both alpha and beta conformation) were polarized in this manner The polarization of the sample was determined from current integration measurements The piezoelectric and pyroelectric coefficients were then measured and compared with those estimated from the polarization theory of Mopsik and Broadhurst, which expresses these coefficients as linear functions of polarization The theory gives an accurate representation of the piezoelectric coefficients, but underestimates the pyroelectric coefficients considerably