Ultrasonic investigation in KTaO3

Dielectric Behaviour of Ba_xSr_1–xTiO₃ Perovskites

“…Recently, we have applied the Green's function technique in observing the field dependent microwave loss 34 and attenuation constant 35 and KDP type ferroelectric36 also in displacive ferroelectics.…”

“…The value of Curie constant (C )is obtained from our previous study Deorani et.al. 22 . We have shown the variation of real part of dielectric constant with temperature in Fig.3 in paraelectric phase for Ba x Sr 1-x TiO 3 for different values of x and also the variation of reciprocal of dielectric constant with temperature in Fig.4 for same values of x..…”

“…al. 21,22 have theoretically studied the temperature and frequency dependence of dielectric constant using the method of double time Green's function in Barium Titatnate, Strontium Titanate and Potassium Titanate, anharmonic ferroelectric crystals, using Silverman -Joseph's modified Hamiltonian taking into account anharmonic effect up to fourth order. There has been considerable interest in the physical properties of mixed crystals as they find interesting applications and their study helps in understanding basic mechanism of mixed crystal formation.…”

“…The aim of the present paper is to study theoretically the dielectric property in polycrystalline mixture of Ba x Sr 1 -x TiO 3 by forming a model Hamiltonian for the polycrystalline mixtures of ferroelectric perovskites and than applying it to Ba x Sr 1-x TiO 3 . Double time Green's function 21 technique is used to obtain thermally averaged correlation functions and hence the observable quantities with the help of model Hamiltonian taking into account anharmonic effect upto fourth order with substitutional defect. For simplicity the ions are assumed nonpolarizable.…”

Frequency and temperature dependent attenuation constant in Barium Titanate

“…Expression for ⎡ A (ω) in these perovskites has already been obtained in our previous studies 18 and it has been shown that the presence of scattering, anharmonic and resonant interaction terms increase the value of ⎡ A (ω), which is also known as the half width of the response of acoustic phonons of mode k.This increase is obtained via the stabilized soft mode frequency Ω, which has an imaginary value in the harmonic approximation but is stabilized in presence of higher order anharmonic term 22 . If one is interested in the anomalies and temperature is not too high, the temperature dependence of Ω is given by 17 Ω 2~K (T-T c ), K being a temperature independent coefficient.…”