Search results for "GST"
showing 10 items of 874 documents
Iekšējās kvalitātes nodrošināšanas sistēmas pilnveide koledžā ''X''
2020
Maģistra darba pētījums “Iekšējās kvalitātes nodrošināšanas sistēmas pilnveide koledžā “X” īstenots nesen dibinātā privātā augstākās izglītības iestādē Rīgā, kurai ir šaura specializācija, t. i., viens studiju virziens un pagaidām tikai viena pirmā līmeņa profesionālās augstākās izglītības programma. Pētījums veikts ar mērķi analizēt un izvērtēt koledžas “X” iekšējās kvalitātes nodrošināšanas sistēmu un izstrādāt ieteikumus koledžas “X” iekšējās kvalitātes nodrošināšanas sistēmas pilnveidošanai. Pētījumā pielietotas zinātnisko pētījumu kvantitatīvās un kvalitatīvās metodes – politisko dokumentu, koledžas “X” iekšējo normatīvo aktu un citu dokumentu, kā arī neatkarīgo ekspertu ziņojumu konte…
CCDC 619252: Experimental Crystal Structure Determination
2007
Related Article: L.Lisnard, P.Mialane, A.Dolbecq, J.Marrot, J.M.Clemente-Juan, E.Coronado, B.Keita, P.de Oliveira, L.Nadjo, F.Secheresse|2007|Chem.-Eur.J.|13|3525|doi:10.1002/chem.200601252
Crystal chemical and dielectric properties of Pb0.5(5-x)LaxNb5-xFexO15system with “tetragonal tungsten bronze” structural type
2005
The lanthanum-lead and iron-niobium coupled substitution in PbNb 2 O 6 have allowed to isolate new materials of a general formula Pb 0.5(5-x) La x Nb 5-x Fe x O 15 crystallising with the tetragonal tungsten bronze structural type. The resulting influence on the lattice parameters, the ferroelectric Curie temperature and Cole - Cole plots are presented. A typical ferroelectric - paraelectric behaviour occurs in the composition range 0 ≤ x ≤ 0.33 while, a relaxor behaviour is observed in the composition range 0.33 < x < 1.
Proton presence and motion in rhenium-oxide films and their application to liquid-crystalline cells
2007
Disordered solid phases, containing appreciable amounts of hydrogen ions, are grown at the surface of rhenium oxide crystals, because of the high reactivity of this compound with ambient moisture. To investigate such phenomena, a comparative study is performed on ground powder and thermally evaporated or sputtered films using x-ray diffraction and micro-Raman spectroscopy. Two types of solid phases were found in the films: HxReO3 distorted perovskite structures, based on corner-sharing ReO6 octahedra as in the bulk crystals, and ordered HReO4 crystalline structures, based on tetrahedral perrhenate ions. The complex impedance measurements on ReO3 films support the hypothesis of mobile hydrog…
Personības veidošanās kolektīvā
1989
Krājumā ietverti materiāli par personības veidošanos skolas un augstskolas kolektīvos. Pētīti kritēriji, kas nosaka personības izveidošanos, individuālo attīstību.
Low-temperature polymorphism in tungsten trioxide powders and its dependence on mechanical treatments
1999
The polymorphism of WO3 powder samples, resulting from mild mechanical treatments and from temperature changes between 30 K and room temperature, has been investigated by using Raman spectroscopy and X-ray di⁄raction. A transition from the monoclinic (I) c-phase to the triclinic d-phase after moderate mechanical treatments has been observed for untreated powder, just what happens when the same samples are rapidly cooled to low-temperature. Evidences of the low temperature monoclinic (II) polar e-phase have been found at room temperature in samples after a stronger milling treatment. The sequence of the low-temperature phase transitions appears to be strongly dependent on the mechanical hist…
Quasi-hydrostatic X-ray powder diffraction study of the low- and high-pressure phases of CaWO4 up to 28 GPa
2014
We have studied CaWO4 under compression using Ne as pressure-transmitting medium at room temperature by means of synchrotron X-ray powder diffraction. We have found that CaWO4 beyond 8.8 GPa transforms from its low-pressure tetragonal structure (scheelite) into a monoclinic structure (fergusonite). The high-pressure phase remains stable up to 28 GPa and the low-pressure phase is totally recovered after full decompression. The pressure dependence of the unit-cell parameters, as well as the pressure volume equation of state, has been determined for both phases. Compared with previous studies, we found in our quasi-hydrostatic experiments a different behavior for the unit-cell parameters of th…
Optical and structural study of the pressure-induced phase transition of CdWO$_4$
2017
Physical review / B 95(17), 174105 (2017). doi:10.1103/PhysRevB.95.174105
Crystal chemistry and phase transitions in mixed niobates crystallizing with tetragonal tungsten bronze structure
1990
Abstract New compounds crystallizing with tungsten bronze structure are reported. A dielectric study and X-ray analysis at various temperatures have allowed to describe some phase transitions.
EXAFS Study of PressureInduced Phase Transition in SrWO4
2005
Pressure-induced scheelite-to-wolframite structural phase transition in SrWO4 was studied using two complementary techniques—x-ray absorption spectroscopy and x-ray diffraction (XRD). In situ XRD and W L3-edge EXAFS measurements were performed using the synchrotron radiation. The experiments were done at room temperature in the pressure range from 0 to 30 GPa using the diamond anvil cell. The XRD results unambiguously show that SrWO4 transforms from the tetragonal scheelite phase to the monoclinic wolframite-type phase at about 11.7 GPa. Locally this transition appears as a change of the tungsten ions coordination from regular tetrahedral to distorted octahedral. The analysis of the EXAFS d…