Marta E. Polomska

Polarized light study of the CsHSO4 and CsDSO4 superprotonic crystals

Abstract The results of an optical polarization study of superprotonic CsHSO 4 and CsDSO 4 crystals in the vicinity of phase transitions are presented. Our observations allow us to state that the temperature of III–II phase transition in `fresh, high quality crystals is 373 K. The temperature of the phase transition of the specimens that have experienced the III–II phase transition earlier is reduced to 330 K. It is established that changes of the domain structure in CsDSO 4 crystals are observed on both increasing and decreasing temperature at 3 K away from the temperature of the superprotonic phase transition. The appearance of the new structure is accompanied by a gradual increase in the conductivity by 1.5–2 order of magnitude and then the conductivity increases abruptly by another two orders of magnitude at the temperature of the superprotonic phase transition.

Ferroelastic domain structure in the vicinity of superionic phase transition in CsDSO4 crystals

Abstract Ferroelastic reversible domain structure with (203) and (101) domain walls is induced in CsDSO4 crystals by [100] and [001] compression at room temperature. About 3–4 K below the superionic phase transition new (101) domain walls appear in the crystal. Changes in the wedge-shaped domain pattern are observed also in (100) cut samples at temperature 3–4 K below Ts, both on heating and on cooling (with thermal hysteresis of ∼ 7 K). The changes of the domain pattern in the close vicinity of Ts are related to an anomaly in thermal expansion along the [001] direction reported at (Ts-3K) by Dilanyan and Shekhtman. Molecular model of the (203) twin is proposed.

DOMAIN WALL ORIENTATION MEMORY AS A RESULT OF CONSECUTIVE FERROIC PHASE TRANSITIONS

Abstract It was shown that pattern of domain structure in ferroic crystals undergoing a sequence of phase transitions, changes and depends on the phase preceding the phase with ferroic arrangement. Two crystals were taken into considerations: β-L1NH4SO4 and (NH4)3H(SeO4)2. The orientation of domain walls, both ferroelectric and ferroelastic, is determined by random domain walls, which appeared in the previous phase both ferroelectric and ferroelastic, or a regular large scale structure, which was found in the vicinity of phase transition in β-LiNH4SO4.

Low-temperature behaviour of (NH4)4H2(SeO4)3 and (ND4)4D2(SeO4)3 superionic conductors

Abstract The structure of (NH 4 ) 4 H 2 (SeO 4 ) 3 and of its deuterated analogue was re-determined at room temperature and at ∼140 K. In the examined temperature range, the same centrosymmetric space group P1 was ascribed to both crystals. A continuous temperature variation of lattice parameters was still apparent there. Splitting of the Raman band at 867 cm −1 , arising from ν 1 vibrations of two-proton donor selenate tetrahedra in (ND 4 ) 4 D 2 (SeO 4 ) 3 , was observed below 215 K. The low-temperature dependence of dielectric permittivity of (NH 4 ) 4 H 2 (SeO 4 ) 3 exhibits a broad maximum which we relate to a glass-like transition and not to a ferroelectric–paraelectric one.

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.

Ferroelastic domain structure of (NH4)3H(SeO4)2 and its deuterated analogue

Abstract The effect of deuteration on ferroelastic-ferroelastic phase transitions and ferroelastic domain structure in (NH4)3H(SeO4)? was investigated. Crystals of various degrees of deuteration were studied. The temperature width of ferroelastic triclinic phase was found to decrease with increasing degree of deuteration. The temperature of superionic (2) - ferroelastic (1) phase transition lowered from 306 K for the non-deuterated crystal to 293 K for the crystal with the highest degree of deuteration. Additional result of deuteration was a change in the pattern of domain structure in the ferroelastic (1) - ferroelastic (2) phase.