Pyroelectric Current Measurements Research Articles

Dielectric and pyroelectric properties of TGS-polystyrene composites

Abstract A composite of triglycine sulphate (TGS) and polystyrene has been fabricated in a multilayer pattern with 2–2 connectivity made up of alternating layers of polystyrene and TGS powder. Samples with TGS powders of varying particle size, ranging from less than 75 μm to more than 400 μm were prepared in the form of thin sheets (2.0 cm × 1.5 cm × 0.15 cm). Samples with same weight percentage (70 to 75%) of TGS, but different particle size, were chosen for dielectric and pyroelectric studies in the ferro- and paraelectric phases. The dielectric constant and loss have been measured in the frequency range of 0.1 to 100 KHz and the pyroelectric current measurements were made by the Byer and Roundy direct method. The magnitude of dielectric constant (ϵ′) and pyroelectric coefficient Py show an increase with increasing particle size and the room temperature values for the biggest particle size are [ϵ′ = 8.3] and Py = 0.6 × 10−10 C cm−2 K−1. Anomalies in ϵ′ and pyroelectric coefficient, indicating the existence of ferroelectricity were observed even for the composites with the lowest particle size of TGS (< 75 μm). A dielectric dispersion in the frequency range 0.1 to 100 KHz and the particle size dependence of pyroelectric coefficient and dielectric constant can be accounted for by assuming non-ferroelectric surface layers at the boundaries of TGS crystallites. The responsivity of TGS-Polystyrene composites for infrared detection has been compared with those of single crystals, hot pressed TGS powders and composites employing other ferroelectrics. The decrease in pyroelectric coefficient with particle size is compensated to some extent by the decrease in dielectric constant, such that responsivity of these composites does not show any marked dependence on particle size.

Heating rate effect on domain structure realignment in gadolinium molybdate crystals

Influence of the heating rate on domain structure realignment processes and associated phenomena in gadolinium molybdate is studied by means of thermal Barkhausen effect, polarized microscopy, pyroelectric current measurements, selective etching. It is shown that the phase transition temperature is lowered when the heating rate is increased. It is supposed that observed effects are associated with mechanical stretching strains in the sample due to heating inhomogenities.

Dielectric and pyroelectric properties of triglycine sulphate-polystyrene composites

Abstract A composite of Triglycine sulphate (TGS) and polystyrene has been fabricated by mixing different particle size TGS powders (75 μm to 400 μm) and polystyrene solution. The dielectric constant has been measured in the frequency range 0.1 to 100 KHz, and the pyroelectric current measurements were made by the Byer and Roundy direct method. Specific heat of the composite was determined by the differential them analysis (DTA) technique. Particle size dependance of dielectric constant, pyroelectric coefficient and responsivity have been studied. Anomalies in ∊′ and Py were observed even in the composite with the lowest particle size of TGS (75 μm). The surface effects have much greater influence on electrical properties but thermal properties are, not affected. This is indicated by a decrease in ∊′ and Py with decreasing particle size of TGS, while specific heat of composite is almost independent of particle size.

Piezoelectricity and pyroelectricity of polyvinylidene fluoride corona‐poled at elevated temperature

AbstractX‐ray diffraction, thermally stimulated depolarization, and piezoelectric and pyroelectric current measurements have been carried out on biaxially oriented polyvinylidene fluoride film, corona‐poled both negatively and positively, at elevated temperature. Larger piezoelectric and pyroelectric coefficients are obtained at lower values of the poling field, when corona charging takes place at elevated temperature rather than room temperature. Negative charging is more effective than positive. The polarization mechanism is dipole alignment, and a conversion of Form‐II crystallites to Form I. The large space‐charge injected by the corona, and trapped in the material, acts through creation of high internal fields, and shows little, if any, piezoelectric and pyroelectric effects of its own.

Pyroelectric and electrocaloric effects in the phase transition region of thin ferroelectrics

The pyroelectric and electrocaloric effects in the phase transition region of thin ferroelectric wafers, as part of a metalferroelectric-metal (MFM) system, are investigated experimentally and theoretically. Experiments on the dynamical pyroelectric effect are carried out on triglycine sulphate crystals (TGS). A theory of dynamical pyroelectric and electrocaloric effects in the presence of an internal electric field (depolarizing, influence of contact and of surface charges) is developed. An expression for the shift of the pyroelectric current maximum temperature (PCMT) with respect to the Curie point is derived and the influence of the electrocaloric effect on this shift is investigated. It is shown that with decreasing thickness of the ferroelectric wafer the phase transition temperature and the PCMT shift to lower temperatures, and also the pyroelectric current maximum decreases. From the pyroelectric current measurements on pure TGS and on TGS doped with L-α-alanine the Curie constant is determined. A...

Pyroelectric detection properties of gadolinium molybdate (gmo)

The pyroelectric detection properties of gadolinium molybdate (GMO) crystals have been studied near and at its 159°C ferroelectric transition temperature. Responsivity and detectivity figures of merit are calculated from measurements of pyroelectric currents induced by white light irradiation and are compared with room temperature figures of merit for TGS and SBN detectors. Since GMO does not exhibit a dielectric anomaly, it can be used as a threshold detector by heating through the transition temperature from a pre-selected temperature increment below the transition. Voltage-sensitive pyroelectric currents at the transition, found previously, permit voltage control of the threshold.

Pyroelectric effect in gadolinium molybdate(GMO)

Measurements of pyroelectric currents in GMO show two major discontinuities in the vicinity of the 159°C phase transition, separated by about 2°K, whose locations do not depend on the heating rate. Applied electric fields neither shift nor broaden these peaks but do enhance the upper 'peak at the expense of the lower one until, at fields of the order of 5,000 v/cm, only the upper peak remains. A tentative explanation of this behavior is offered, based on recent studies of the structure and possible polarization and switching mechanisms in GMO.

Are rare earth orthochromites ferroelectric?

On the basis of dielectric hysteresis, electrical conductivity and pyroelectric current measurements, some polycrystalline rare earth orthochromites are suspected to be associated with ferroelectric phenomena which are not compatible with the assignment of a centrosymmetric space group (Pbnm). Sur la base mesures d'hystérèse de conductibilité électrique et de courant pyroélectrique, quelques orthochromites de terre rare à l'état de poudre semblent être associés avec des phénomènes ferroélectriques, ce qui est incompatible avec un groupe centro-symétrique (Pbnm).