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1.
I. N. Flerov V. D. Fokina M. V. Gorev A. D. Vasiliev A. F. Bovina M. S. Molokeev A. G. Kocharova N. M. Laptash 《Physics of the Solid State》2006,48(4):759-764
Precision studies of the thermophysical properties and structure of an (NH4)2WO2F4 crystal have been performed. It was established reliably that there is a sequence of two phase transitions at T 1 = 201 K and T 2 = 160 K characterized by wedging out of an intermediate phase with an increase in pressure. The role of tetrahedral and octahedral ionic groups in the mechanism of the structural transitions was determined. 相似文献
2.
Different ammonium fluoroferrates (NH4)xFeF2x (2≤x≤3) have been investigated. The thermal decomposition of the compounds obtained can be interpreted by their identical crystal structures (cryolite type). The decomposition products of all ammonium fluoroferrates formed in initial stage are isostructural of NH4FeF4. The decomposition is accompanied by the partial reduction of Fe(III) to Fe(II) by ammonium isolated. The end product of the thermal decomposition is FeF2 and FeF3 mixture. 相似文献
3.
Yu. V. Gerasimova A. S. Krylov A. N. Vtyurin N. M. Laptash S. V. Goryaĭnov 《Physics of the Solid State》2008,50(8):1534-1537
Raman spectra of a polycrystalline sample of the perovskite-like oxyfluoride (NH4)3TiOF5 are measured in the frequency region 100–3600 cm?1 at temperatures ranging from 91 to 370 K under hydrostatic pressures of up to 9 GPa, which include the range of the phase transition from the orientationally disordered cubic phase to the low-symmetry phase. Anomalies in the spectral parameters due to the phase transition are revealed in the range of vibrations of TiOF5 octahedral groups. 相似文献
4.
M. V. Gorev E. V. Bogdanov I. N. Flerov A. G. Kocharova N. M. Laptash 《Physics of the Solid State》2010,52(1):167-175
The thermal expansion along the principal crystallographic axes of the (NH4)2WO2F4 and (NH4)2MoO2F4 oxyfluorides has been studied. The anomalous behavior of α
i
(T) due to the phase transitions has been revealed at T
1 = 271.4 K and T
2 ≈ 180 K for the molybdate and at T
1 = 201.5 K and T
2 ≈ 161 K for the tungstate. The quantities dT/dp and dT/dσ
i
, which characterize the dependence of the phase transition temperatures on the hydrostatic and uniaxial pressures, have been
determined from analyzing the results of studies of the thermal expansion and heat capacity with the use of the Pippard relations.
The p-T and α
i
-T phase diagrams reflect different characters of the influence of the pressure on the stability of the initial and distorted
phases of the oxyfluorides. The magnitudes of the extensive and intensive barocaloric effects determined in the vicinity of
the structural phase transitions are as follows: ΔS
BCE varies from approximately −10 to −17 J/mol K and ΔT
AD ≈ 8−17 K for the molybdate and ΔS
BCE varies from approximately −10 to −17 J/mol K and ΔT
AD ≈ 8−13 K for the tungstate. 相似文献
5.
A. S. Krylov Yu. V. Gerasimova A. N. Vtyurin V. D. Fokina N. M. Laptash E. I. Voĭt 《Physics of the Solid State》2006,48(7):1356-1362
The Raman scattering spectra of polycrystalline samples of the (NH4)3WO3F3 perovskite-like oxyfluoride were measured at frequencies of 70–3600 cm?1 in the temperature range 93–323 K, including the transition from the orientationally disordered cubic phase to the low-symmetry phase. Transitional anomalies in the spectral parameters were revealed in the frequency ranges of internal vibrations of the ammonium ions and WO3F3 octahedral groups. An analysis of the experimental results allowed the conclusion that the phase transition under study is associated primarily with the ordering of the octahedral groups. 相似文献
6.
Hydrolysis of NH4TiOxF5-2x (x0.4) (I) was investigated by 19F, 17O, and 49Ti NMR. The interaction of complex I with water is accompanied by the formation of [TiF6]2- and multinuclear titanium forms. The composition of the main forms resulting from hydrolysis of I has been established. The bonding of titanium octahedra into dimers and other oligomers occurs by formation of hydroxyl bridges, considerably lowering the pH of the solution. Close analogy has been found between hydrolysis of the title complex and that of titanium tetrafluoride. 相似文献
7.
Fluorine-19 and natural abundance 17O and 183W NMR spectroscopy were employed for the characterization of aqueous solutions of (NH4)2WO2F4 and (NH4)3WO3F3. Dissolution of the (NH4)2WO2F4 complex is accompanied by its partial acid hydrolysis to give the trans(mer)-dimer, [W2O5F6]4−, and unreacted cis-[WO2F4]2−. The cis(fac)-[W2O5F6]4− anion is the major soluble product resulting from the alkaline hydrolysis of (NH4)2WO2F4 along with the isolation of the solid (NH4)2WO3F2. In addition, the edge-bridging dimer, [W2O6F4]4−, and the cyclic trimer, [W3O9F6]6−, are also suggested as hydrolysis products. Decomposition of (NH4)3WO3F3 occurs in aqueous solution to give NH4WO3F. 相似文献
8.
(NH4)2MoO2F4 single crystals were grown and studied using polarization-optical methods, and the birefringence was measured in the temperature range 90–350 K. The following sequence of phase transitions is revealed: G 0 ? G 1 ? G 2. It is established that the phase transition at T 01 ≈ 267 K is of the first order and exhibits thermal hysteresis δT 01 ≈ 0.6 K. A weak anomaly is found in Δn(T) at T 02 ≈ 180 K. The crystals are shown to retain the orthorhombic symmetry during the phase transitions. 相似文献
9.
N. M. Laptash E. B. Merkulov I. G. Maslennikova 《Journal of Thermal Analysis and Calorimetry》2001,63(1):197-204
The thermal behaviour of ammonium oxofluorotitanates (NH4)3TiOF5, (NH4)2TiOF4 and NH4TiOF3 was investigated by thermoanalytical, X-ray and IR spectroscopic methods. The first decomposition stages under quasi-isobaric conditions are characterized by the formation of (NH4)2TiF6 and ammonium oxofluorotitanate with the less content of ammonium and fluorine than in the initial compound. The decomposition process is accompanied by the Ti(IV) reducing due to ammonia evolved. The new ammonium oxofluorotitanate of high volatility was isolated and characterized. Ammonium-containing non-stoichiometric titanium oxyfluorides are the final products of thermal decomposition of ammonium oxofluorotitanates.This revised version was published online in November 2005 with corrections to the Cover Date. 相似文献
10.
V. Ya. Kavun B. V. Bukvetskii N. M. Laptash I. G. Maslennikova S. S. Sergienko 《Journal of Structural Chemistry》2001,42(5):771-776
The crystal structure of NH4TiF5 (I) was determined (monoclinic crystals, a = 14.683(1), b = 6.392(1), c = 20.821(2) , = 110.538(2); space group P21/n, Z = 4). Structure I is built from infinite zigzag chains of TiF6 octahedra linked by their cis-vertices in the [101] direction; the chains are connected by the ammonium ions forming hydrogen bonds. The chains of octahedra with the surrounding ammonium ions are staggered in the crystal lattice of I. 19F and 1H NMR spectroscopy was used to study the dynamics of the complex ions in NH4TiF5 in the temperature range 270-530 K. Types of ionic motion in the fluoride and proton subsystems were determined, and activation energies evaluated. 相似文献