J. Wolak

Ferroelastic domains and ferroelastic phase transition of (NH4)4LiH3(XO4)4, X: S, Se

Abstract Dielectric and optical investigations of (NH4)4LiH3(SO4)4 and (NH4)4LiH3(SeO4)4 single crystals showed that these crystals are new ferroelastic below 233 K and 267 K respectively. X-ray studies demonstrated that above mentioned crystals are isomorphous with other representatives of Me4LiH3(XO4)4 family and undergo transition from paraelastic tetragonal (P41 or P43) to ferroelastic monoclinic (P21) phase.

Superionic phase transition in Rb4LiH3(SO4)4, Rb4LiH3(SeO4)4 and K4LiH3(SO4)4 single crystals

Abstract DTA studies of a new family of ferroelastic crystals of Me4LiH3(XO4)4 stoichiometry revealed at Ts another phase transition in the paraelastic phase, accompanied by an anomalous increase in the capacitance. Complex impedance method was used to study temperature variation of electric conductivity and its anisotropy of Rb4LiH3(SO4)4, Rb4LiH3(SeO4)4 and K4LiH3(SO4)4 single crystals. The bulk conductivity of the crystals varies from 10−6 to 10−4 (ωm)−1 in the temperature range from ∼ 400 K to temperatures below melting. The conductivity σc is ∼ one order of magnitude lower than σa ∽ σb. At Ts the activation energy Wa ∽ Wb decreases from 0.94 – 1.35 eV below Ts to 0.27 –0.28 eV at T > Ts. Comparison of the data with the crystallographic structure allowed us to classify the transition as superionic.

Dielectric studies of psnt single crystals

Abstract The paper reports results of dielectric studies of Pb(Sc0.5Nb0.2Ta0.3)O3 single crystals (Nb and Ta ions having the same effective radius) as grown, and thermally treated. Dielectric anomaly at 317 K can be ascribed to the ferroelectric paraelectric phase transition, whereas the disordered phase of the mixed crystal exhibits dielectric anomaly at ∼ 306 K. The existence of polar microregions in a wide temperature range above the Curie point was observed by us directly in dielectric measurements and the activation energy of 0.49 eV can be ascribed to the polar clusters.

Low frequency dielectric relaxation in oxidic pyrochlores Cd2Nb2O7 and Cd2Ta2O7

Abstract Electric permittivity of Cd2Nb2O7 and Cd2Ta2O7 single crystals was investigated in the frequency region of 1 kHz-1 MHz. A low-frequency dielectric relaxation in these isostructural pyrochlores is observed over the whole temperature region from 90 to 300 K, but only below phase transitions. The relaxation results from thermal displacements of the “seventh” oxygens with respect to Cd2+ ions of the (CdO8)n- polyhedra. In Cd2Nb2O7, the dielectric relaxation is also determined by thermal vibrations of domain walls in ferroelectric phase.

XRD and Raman spectroscopy studies of (Bi1–xLaxFeO3)0.5(PbTiO3)0.5 solid solution

(Bi1–xLaxFeO3)0.5(PbTiO3)0.5 solid solution obtained by mechanochemical synthesis was characterized by X-ray diffraction (XRD), atomic force microscopy and Fourier transform near-infrared Raman spectroscopy. The single-phase solid solution with La content between x = 0 and 0.5 was prepared. The solid solution exhibits a tetragonal symmetry P4mm for 0 ≤ x ≤ 0.2. It was found that Raman spectra undergo a significant change for the solid solution with La content between x = 0.16 and 0.20. It may indicate the existence of a morphotropic boundary in this range of the La content. Detailed XRD study on (Bi0.5La0.5FeO3)0.5(PbTiO3)0.5 pointed to a rhombohedral symmetry R3c.

Ferroelastic Domain Structure in some Superprotonic Conductors

The paper reviews the results of our studies concerning the ferroelastic domain structure in the crystals exhibiting superprotonic conductivity. We would like to show the ferroelastic domain structure and its temperature behaviour in solid acids which belong to the family of crystals with a general formula M x Li y H z (XO 4 )(x + y + z)/2 (M = Rb,K,Cs,NH 4 ; X = S and Se). For the majority of crystals, which belong to that family, the transition to the phase with high proton conductivity is simultaneously the ferroelastic-paraelastic one. However, this does not apply to all crystals of the family. Therefore, a question arises about the role of the phenomenon of ferroelasticity in the superprotonic phase transition. Depending on x,y and z, there are different groups of crystals. Our paper presents the results of temperature evolution of ferroelastic domain pattern at ferroelastic-superprotonic phase transitions as well as at other structural phase transitions, which appear in different crystal groups.

Some applications of microwave ceramic ring resonator in laboratory measurements

Abstract We discussed application of a pillbox and open ring short circuited dielectric resonators. A confining of the magnetic field of TE011 mode in the empty region of ring resonator enabled us to employ the resonator as EPR cavity. Experimental results are shown.

Molecular dynamics in (NH4)3H(SeO4)2 at superionic phase transitions: Raman spectroscopy study

This article presents detailed temperature Raman spectra changes at two superprotonic phase transitions of (NH4)3H(SeO4)2. The study of temperature evolution of Raman spectra has shown great changes at low temperature phase transitions at T 3 and T 4, whereas only very small changes have been observed at the two superionic transformations at T 1S and T 2S. The stretching vibration frequencies of proton donor and acceptor selenate tetrahedra have been found to change slightly in the temperature range 295–341 K with a slope change at T 1S and T 2S. A slope change in temperature dependence of proton conductivity has also been observed at the same temperatures.

Molecular dynamics study in the vicinity of ferroelastic : Paraelastic phase transition of [(NH4)1-xRbx]3H(SO4)2

First FT NIR Raman studies of [(NH4)1−x Rbx]3H(SO4)2 in the vicinity of ferroelastic-paraelastic/superprotonic phase transitions TS are presented. Investigations concentrated on molecular dynamics behavior of SO4 and HSO4 entities, which constitute isolated dimers in the crystals. It was found that orientational disorder in the crystals decreases with increasing Rb content. In temperature behavior of band positions and Raman line width related to internal vibrations of molecular groups conspicuous changes were found in the vicinity of TS. The difference between the first and successive heating—cooling runs and for all mixed crystals can be related to the difference in ferroelastic domain states.

Nir-raman studies of poly(ethylene oxide) + (NH4)4H2(SeO4)3 polymer electrolyte

Abstract Infrared Raman scattering studies were made on a composite of poly(ethylene oxide) (PEO) polymer+(NH4)4H2(SeO4)3 crystal. Comparison of the spectra obtained for the composite of PEO+(NH4)4H2(SeO4)3 and the mixture of dry powders of the same contents suggests the existence of a complex in the composite. The degree of crystallinity of the polymer increases with growing content of (NH4)4H2(SeO4)3 in the composite.