V. V. Grebenev

Investigation of the structural conditionality for changes in physical properties of K3H(SO4)2 crystals

AbstractWith the aim of elucidating the nature of anomalies in the physical properties of K3H(SO4)2 crystals that arise as the temperature grows, the dielectric and optical properties of the crystals are studied, an X-ray diffraction analysis of single-crystal and polycrystalline specimens are performed, and the morphology and chemical composition are studied by scanning electron microscopy and energy-dispersive X-ray spectroscopy. As a result of the studies performed, a phase transition from the phase with the monoclinic symmetry (space group C2/c) to the phase with the trigonal symmetry (space group R

Investigation of the structure and properties of (Kx(NH4)1 − x)3H(SO4)2 single crystals

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M(m)H(n)(XO4)((m+n)/2) crystals: structure, phase transitions, hydrogen bonds, conductivity. I. K9H7(SO4)8·H2O crystals--a new representative of the family of solid acid conductors.

m) is found in a number of K3H(SO4)2 specimens at a temperature of ≈457 K, the responsibility of the dynamically disordered hydrogen-bond system for the rise of high proton conductivity in the high-temperature phases of the crystals of this family is confirmed, and data on the solid-phase reactions proceeding at high temperatures are obtained.

Growth and properties of mixed K2NixCo1−x(SO4)2 · 6H2O crystals

At elevated temperatures the crystals of complex acid salts K m H n (SO 4 )(m + n)/2 . xH 2 O (0 ≤ x ≤ 1, m > 3, n ≥ 1) exhibit an anomalous temperature behavior of the dielectric permittivity and conductivity similar to the behavior observed in pure KHSO 4 at the structural phase transition or on melting. This unusual behavior is due to the formation of multiphase states at higher temperatures where phases with different chemical composition coexist. It is shown that K 3 H(SO 4 ) 2 undergoes a ferroelastic phase transition between the point groups 3 2/m with anomalously slow kinetics at 463 K while the multiphase state is formed near 480 K

Phase Transitions in Cs 5 (HSO 4 ) 2 (H 2 PO 4 ) 3 Crystal

The influence of isomorphous replacement in the cation sublattice on the kinetics of the phase transition in single crystals of the solid solutions (Kx(NH4)1 − x)mHn(SO4)(m + n)/2 · yH2O belonging to the K3H(SO4)2-(NH4)3H(SO4)2-H2O salt system was studied. Superproton phase transitions for the end compositions of this system have been found earlier. The optical and thermal properties of crystals with the composition (K,NH4)3H(SO4)2 in the temperature range from 295 to 500 K were investigated, and the crystal structure was determined at 295 K. The results of the study and the comparison with the literature data show that the replacement of potassium atoms with ammonia leads to a fundamental change in the kinetics of the phase transition, the phase-transition temperature remaining virtually unchanged.

Elemental analysis of mixed K2NixCo1–x(SO4)2 ∙ 6H2O crystals

To elucidate the effect of isomorphic substitution on the kinetics of phase transitions, single crystals of (Kx(NH4)1−x)mHn(SO4)(m + n)/2 · yH2O solid solutions are grown from the K3H(SO4)2-(NH4)3H(SO4)2-H2O system, whose end members are known to undergo superprotonic phase transitions of fundamentally different kinetics. The chemical composition of the single crystals grown is determined by energy dispersive X-ray microanalysis. The thermal and optical behavior of (K,NH4)9H7(SO4)8 · H2O single crystals is studied in the temperature range 295–420 K and the crystal structure at 295 K is determined. A comparison of the results of the studies with data for crystal K9H7(SO4)8 · H2O published earlier shows that the substitution of ammonium for potassium atoms lowers the temperature of the structural phase transition by 8 K.

Effect of growth conditions on the functional properties of K2Co(SO4)2·6H2O crystals

To reveal the structural conditionality for anomalies in physical properties, including dielectric and optical properties, diffraction studies of K9H7(SO4)8·H2O crystals were performed using synchrotron radiation in the temperature range 293-450 K and determined at 405 K, taking H atoms into account. The results indicate that the occurrence of high conductivity in K9H7(SO4)8·H2O crystals with a temperature increase is associated with the outward diffusion of water molecules, hydrogen-bond network rearrangement and the formation of channels for the possible motion of K(+) ions. A rearranged system of hydrogen bonds consists of permanent bonds and partly of dynamically disordered bonds. Hydrogen-bond rearrangement and the hindered back diffusion of water to the crystal bulk stabilize the high-temperature crystal structure right down to room temperature.

Temperature-induced changes in the single-crystal structure of K9H7(SO4)8 · H2O

Optically homogeneous mixed K2NixCo(1 − x)(SO4)2 · 6H2O crystals are grown from solutions of different compositions by the temperature-reduction technique in static and dynamic regimes. The optical characteristics of the grown crystals are measured: transmittance reaches 80% in the wavelength range of 240–290 nm and no more than 9% in the visible spectral range. The thermal stability of the crystals is studied. It is established that the thermal stability of mixed K2NixCo1 − x(SO4)2 · 6H2O crystals is higher than that of K2Co(SO4)2 · 6H2O crystal. The defects of the mixed crystals grown in static and dynamic regimes are investigated by X-ray topography.