W. Windsch

Electron spin-lattice relaxation in Mn2+-doped ferroelectric TSCC

Abstract The spin-lattice relaxation of ferroelectric TSCC: Mn 2+ has been investigated by means of the electron spin echo method in the range between 4.2 and 160 K. In the vicinity of the phase transition an anomalous increase of T 1 has been detected deviating from the spin-lattice relaxation in the remaining temperature range.

Estimation of critical exponents for the ferroelectric transition in Mn2+-doped tris-sarcosine calcium chloride (TSCC) by means of EPR

Abstract The static rotation angle of the EPR fine-structure tensor of Mn 2+ centers of ferroelectric TSCC correlates with the order parameter. Its temperature dependence shows two distinct regions. In the vicinity of the phase transition temperature the critical exponent is β = 0.322 ± 0.012, below this critical region its temperature dependence points at a phase transition of weak first order.

Critical fluctuations in trissarcosine calcium chloride (TSCC) observed by the electron spin echo (ESE) method

Abstract In the close vicinity of the second order phase transition in manganese doped ferroelectric TSCC a critical T 2 effect of the paramagnetic Mn 2+ center has been detected by means of the electron spin echo method. The strong decrease of T 2 required the highest time resolution and sensitivity of the spectrometer. The theoretical explanation of the observed effect shows, that TSCC is a ferroelectric material of relaxational type with anisotropic interaction.

EPR investigations of critical order parameter fluctuations in ferroelectric tris-sarcosine calcium chloride (TSCC)

Abstract The EPR spectra of Mn 2+ -doped TSCC show in the immediate vicinity of the ferroelectric transition a critical line broadening. It is angular-dependent and may be related to a critical slowing down of the polarization fluctuations at the phase transition point. The observed line asymmetry points at a strong influence of the real structure of the crystal on the effects investigated.

The concentration dependence of the ferroelectric transition temperature of the solid solution of TSCC and TSCB

Abstract The concentration dependence of the ferroelectric transition temperature Tc of single crystals of the solid solution tris-sarcosine calcium chloride1−x bromidex is studied experimentally by measurement of the static dielectric constant ϵb and described by the empirical relation T c (X) = T c (0) [1−(X/X c )] 1 2 . The Ising model with transverse field and the model of coupled anharmonic oscillators are used to explain the concentration dependence of the transition temperature Tc.

On the pressure dependence of the phase transition temperature for structural phase transitions

Abstract The model of coupled anharmonic oscillators is used to investigate the influence of hydrostatic pressure on the phase transition temperature. Assuming that the model parameters depend on the distance between the ions of the lattice according to some power laws explicit expressions for the pressure dependence of the phase transition temperature are obtained for displacive type transitions both in the classical limit and in the quantum case and for order-disorder type transitions in the classical limit. The theoretical results are used to elucidate the observed experimental situation in tris -sarcosine calcium bromide (TSCB).

On the pressure dependence of the phase transition temperature in hydrogen-bonded ferroelectrics

Abstract The model of coupled anharmoic oscillators is used to investigate the influence of hydrostatic pressure on the phase transition temperature in hydrogen-bonded ferroelectrics. Assuming that the model parameters depend on the distance between the ions of the lattice according to some power laws explicit expressions for the pressure dependence of the phase transition temperature for quantum ferroelectrics of order-disorder type are obtained. The theoretical results are in good agreement with the observed experimental findings in KDP and DKDP.