Browsing by Author "Dolbinina, V. V."
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Item Brillouin light scattering anomalies and new phase transition in Cs5H3(SO4)4 crystals(2000) Lushnikov, Sergey G.; Shuvalov, L. A.; Dolbinina, V. V.; Schmidt, V. HugoThe behavior of hypersonic longitudinal acoustic phonons at temperatures ranging from 290 to 370 K in a crystal of Cs5H3(SO4)4·nH2O was studied by Brillouin light scattering. Anomalies in the temperature dependences of the frequency shift and spectral width of the Brillouin components in the vicinity of T=360K were observed. We found a “point of isotropization” near 360 K where C11=C33=2.6X10 10 N/m2 We attribute it to an isostructural phase transition from P63/mmc⇔P63/mmc where the apparent acoustic symmetry changes from hexagonal to cubic. Possible models for the phase transition have been discussed.Item Brillouin light scattering anomalies and new phase transition in Cs5H3(SO4)4 crystals(2000-02) Lushnikov, Sergey G.; Schmidt, V. Hugo; Shuvalov, L. A.; Dolbinina, V. V.The behavior of hypersonic longitudinal acoustic phonons at temperatures ranging from 290 to 370 K in a crystal of Cs5H3(SO4)4·nH2O was studied by Brillouin light scattering. Anomalies in the temperature dependences of the frequency shift and spectral width of the Brillouin components in the vicinity of were observed. We found a “point of isotropization” near 360 K where We attribute it to an isostructural phase transition from P63/mmc⇔P63/mmc where the apparent acoustic symmetry changes from hexagonal to cubic. Possible models for the phase transition have been discussed.Item Influence of NH4-Rb substitution on the phase transitions with different kinds of proton disorder in mixed [(NH4)1-xRbx]3H(SO4)2 crystals(1998-09) Baranov, A. I.; Dolbinina, V. V.; Yakushkin, E. D.; Vinnichenko, Yu. V.; Schmidt, V. Hugo; Lanceros-Mendez, S.The role of ammonium ions in order–disorder ferroelastic, ferroelectric and structural phase transitions was studied in mixed [(NH4)1–x Rb x ]3H(SO4)2 0 < x < 1 crystals by dielectric spectroscopy and ac calorimetry. A new superprotonic phase was detected in compounds with x > 0·6. It was found that small Rb concentrations, x < 0·05, strongly smear out the temperature anomalies of dielectric constant and specific heat for phase transitions II–III, III–IV, IV–V and V–VIII. At x > 0·09 these phase transitions are fully suppressed. Finally, for Rb concentrations 0·05 < x < 0·9 a proton glass phase appears below 35 K.Item Phase diagram and dielectric properties of mixed Cs1-x(NH4)xH2PO4 crystals(2002) Baranov, A. I.; Dolbinina, V. V.; Lanceros-Mendez, S.; Schmidt, V. HugoInfluence of NH4 M Cs substitution has been studied in the mixed Cs 1 m x (NH 4 ) x H 2 PO 4 crystals system by means of dielectric measurements. The x-T phase diagram was determined: for ammonium concentrations up to 0.1 the system has a monoclinic paraelectric phase with a transition into a ferroelectric phase whose temperature increases with increasing ammonium concentration. For ammonium concentration 0.4 to 1.0 the system shows a tetragonal paraelectric phase and a transition into an antiferroelectric phase. No solid solutions with concentrations between 0.1 and 0.4 could be grown. The system was further studied with the quasi-one-dimensional Ising model and the three-dimensional anisotropic Ising model.