Thermal and dielectric studies of (ND)MoOF crystals undergoing successive phase transitions at T = 272 K and T = 181 K showed that deuteration is accompanied by an increase in the chemical pressure in the crystal lattice (Δp ≈ 0.02 GPa), which shifts the Cmcm ↔ Pnma transformation for the first order to the tricritical point. The direct participation of ammonium groups in the mechanism of structural distortions is demonstrated by a decrease in the entropy of the high-temperature phase transition (ΔS = R ln 6.
View Article and Find Full Text PDFSingle crystals of silicon double salt (NH)SiF = (NH)SiF·NHF = (NH)[SiF]F were grown and studied by the methods of polarization optics, X-ray diffraction and calorimetry. A sequence of symmetry transformations with the temperature change was established: P4/mbm (Z = 2) (G) ↔ Pbam (Z = 4) (G) ↔ P2/c (Z = 4) (G) ↔ P1[combining macron] (Z = 4) (G) ↔ P2/c (Z = 8) (G). Crystal structures of different phases were determined.
View Article and Find Full Text PDFActa Crystallogr B Struct Sci Cryst Eng Mater
December 2014
An unusual phase transition P4/mnc → Pa\bar 3 has been detected after cooling the (NH4)3TiF7 compound. Some TiF6 octahedra, which are disordered in the room-temperature tetragonal structure, become ordered in the low-temperature cubic phase due to the disappearance of the fourfold axis. Other TiF6 octahedra undergo large rotations resulting in huge displacements of the F atoms by 1.
View Article and Find Full Text PDFJ Phys Condens Matter
May 2010
The thermal expansion along the a, b and c axes of a (NH(4))(2)NbOF(5) crystal was measured from 120 to 300 K. Anomalies of α(T) associated with previously reported phase transitions Cmc2(1) --> C2 --> 1a were observed along all directions at T(1) = 259.3 K and T(2) = 220.
View Article and Find Full Text PDFZh Nevrol Psikhiatr Im S S Korsakova
July 2010
The complex research, including clinical scales (FIM, Mayo-Portland) and data on stabilography and electroencephalography (EEG) studies, was conducted in 10 patients with posttraumatic Korsakov's syndrome (KS) before and after the rehabilitation course using stabilo-training (ST) with feedback (7-12 sessions). A control group consisted of 18 healthy people. In patients with KS, more severe cognitive (memory) disorders were noted before ST that was correlated with the maximal reduction of coherence in all frequency bands in frontal and parietal-occipital areas as well as in the long diagonal pairs between the left frontal and the right parietal-occipital areas which was most distinct for the alpha-band.
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