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1.

Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Pogoreltsev E. I., Flerov I. N., Kartashev A. V., Bogdanov E. V., Laptash N. M.
Заглавие : Heat capacity, entropy, dielectric properties and T–p phase diagram of (NH4)3TiF7
Коллективы : Russian Foundation for Basic Research [15-02-02009]; Council on Grants from the President of the Russian Federation for the Support of Leading Scientific Schools of the Russian Federation [NSh-924.2014.2]
Место публикации : J. Fluor. Chem.: Elsevier Science, 2014. - Vol. 168. - P.247-250. - ISSN 0022-1139, DOI 10.1016/j.jfluchem.2014.10.016. - ISSN 1873-3328
Примечания : Cited References: 16. - This work was supported by the Russian Foundation for Basic Research (Grant no. 15-02-02009), and the Council on Grants from the President of the Russian Federation for the Support of Leading Scientific Schools of the Russian Federation (Grant no. NSh-924.2014.2).
Предметные рубрики: CRYSTAL-STRUCTURE
TRANSITIONS
FLUORIDES
NH4F
Ключевые слова (''Своб.индексиров.''): cubic fluorides--phase transitions--dielectric--phase diagram--calorimetry
Аннотация: Successive phase transitions G1 -- G2 -- G3 in the double salt (NH4)(3)TiF7 have been studied by detailed calorimetric, DTA under hydrostatic pressure and dielectric measurements. Rather large entropy jumps at phase transition points were found to be followed by large additional contributions associated with the temperature dependence of the excess heat capacity. The permittivity behaviour and the tangent of the dielectric losses proved the nonferroelectric nature of both transformations. Two triple-points were found on the temperature-pressure phase diagram, suggesting the existence of a hypothetical parent G0 = Pm-3m cubic phase. A direct transformation between high (G0) and low (G3) temperature cubic phases takes place at p 0.41 GPa with a baric coefficient dT(G0) -- (G3)/dp = -40 K/GPa. (C) 2014 Elsevier B.V. All rights reserved.
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2.

Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Krylov A. S., Vtyurin A. N., Voronov V. N., Krylova S. N.
Заглавие : Manifestations of Structural Phase Transitions in a Rb2KLuF6 Crystal in Its Raman Spectra
Коллективы : Russian Foundation for Basic Research [16-02-00102, 18-02-00754]
Место публикации : Opt. Spectrosc. - 2019. - Vol. 126, Is. 4. - P.341-345. - ISSN 0030-400X, DOI 10.1134/S0030400X1904012X. - ISSN 1562-6911(eISSN)
Примечания : Cited References: 27. - This work was supported by the Russian Foundation for Basic Research, project nos. 16-02-00102, 18-02-00754.
Предметные рубрики: SCATTERING
ELPASOLITES
LUMINESCENCE
TRANSFORMATIONS
FLUORIDES
Аннотация: The Raman spectra of an Rb2KLuF6 crystal are studied in the temperature range from 8 to 375 K, which includes two phase transitions: one of which proceeds from a cubic to a tetragonal phase, while the other transition takes place from a tetragonal to a monoclinic phase. An analysis of the temperature dependences of parameters of spectral lines shows that the former transition is of the second kind, while the latter transition is of the first kind, close to the tricritical point. It is shown that the structural phase transitions in the Rb2KLuF6 double perovskite are not associated with disordering. The former transition is associated with rotations of LuF6 octahedra around the fourth-order axis, while the latter transition is related with rotations of octahedra and displacements of rubidium ions.
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3.

Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Flerov I. N., Gorev M. V., Fokina V. D., Bovina A. F., Bogdanov E. V., Pogoreltsev E. I., Laptash N. M.
Заглавие : Disorder and phase transitions in oxyfluoride (NH4)(3)Ta(O-2)(2)F-4
Место публикации : J. Fluor. Chem. - 2011. - Vol. 132, Is. 10. - P.713-718. - ISSN 0022-1139, DOI 10.1016/j.jfluchem.2011.05.012
Примечания : Cited Reference Count: 19. - Гранты: This work was supported by the Council on Grants from the President of the Russian Federation for the Support of Leading Scientific Schools of the Russian Federation (NSh-4645.2010.2).Финансирующая организация: Council on Grants from the President of the Russian Federation for the Support of Leading Scientific Schools of the Russian Federation [NSh-4645.2010.2]
Предметные рубрики: HEAT-CAPACITY
COMPLEXES
RB2KTIOF5
FLUORIDES
CRYOLITE
Ключевые слова (''Своб.индексиров.''): cubic oxyfluorides--structural disorder--phase transitions--entropy--permittivity--pressure effect--cubic oxyfluorides--entropy--permittivity--phase transitions--pressure effect--structural disorder
Аннотация: Calorimetric, X-ray, dielectric and DTA under pressure measurements have been performed on oxyfluoride (NH4)(3)Ta(O-2)(2)F-4. The succession of nonferroelectric phase transitions was found associated with the order-disorder processes. The comparative analysis tantalate with related niobate has revealed the important role of the central atom in the physical properties behavior, mechanism of structural distortions and barocaloric effect in oxyfluorides with the eight-coordinated anionic polyhedra. (C) 2011 Elsevier By. All rights reserved.
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4.

Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Atuchin V. V., Isaenko L. I., Kesler V. G., Kang L., Lin Z. S., Molokeev M. S., Yelisseyev A. P., Zhurkov S. A.
Заглавие : Structural, spectroscopic, and electronic properties of cubic G0-Rb2KTiOF5 oxyfluoride
Место публикации : J. Phys. Chem. C: American Chemical Society, 2013. - Vol. 117, Is. 14. - P.7269-7278. - ISSN 1932-7447, DOI 10.1021/jp401391y
Примечания : Cited References: 80. - This study was supported by SB RAS (Grant 28.13), the National Natural Science Foundation of China under Grants 11174297 and 91022036, and the National Basic Research Project of China (Nos. 2010CB630701 and 2011CB922204).
Предметные рубрики: RAY PHOTOELECTRON-SPECTROSCOPY
SURFACE CHEMICAL-STABILITY
EFFECTIVE IONIC-RADII
PHASE-TRANSITIONS
CRYSTAL-GROWTH
HEAT-CAPACITY
CORE LEVELS
RB2KTIOF5
FLUORIDES
OXIDES
Аннотация: The G0-Rb2KTiOF5 single crystals with dimensions up to nearly a centimeter in size have been prepared by slow solidification method. The elpasolite-related crystal structure of G0-Rb2KTiOF5 has been refined by Rietveld method at T = 298 K (space group Fm (3) over barm, Z = 4, a = 8.880(1) angstrom, V = 700.16(2) angstrom(3); R-B = 2.66%). The wide optical transparency range of 0.25-9 mu m and forbidden band gap of E-g = 3.87 eV have been obtained for the G0-Rb2KTiOF5 crystal. Dominating photoluminescence bands at 3.36 and 2.33 eV are related to free and self-trapped excitons, respectively. The electronic structure of G0-Rb2KTiOF5 has been evaluated by X-ray photoelectron spectroscopy and calculated with the first-principles methods. A good agreement between theoretical and experimental results has been achieved. Chemical bonding effects have been discussed for all metal ions using binding energy difference parameters and a wide comparison with related oxides and fluorides. The competition between O2- and F- ions for metal valence electrons has been found.
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5.

Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Xia, Zhiguo, Molokeev M. S., Oreshonkov A. S., Atuchin V. V., Liu R. S., Dong C.
Заглавие : Crystal and local structure refinement in Ca2Al3O6F explored by X-ray diffraction and Raman spectroscopy
Место публикации : Phys. Chem. Chem. Phys.: Royal Society of Chemistry, 2014. - Vol. 16, Is. 13. - P.5952-5957. - ISSN 1463-9076, DOI 10.1039/c3cp53816h. - ISSN 1463-9084
Примечания : Cover illustration: Graphical abstract from this article. - Cited References: 34. - This present work was supported by the National Natural Science Foundations of China (Grant No. 51002146, 51272242), Natural Science Foundations of Beijing (2132050), the Program for New Century Excellent Talents in University of Ministry of Education of China (NCET-12-0950), Beijing Nova Program (Z131103000413047) and Beijing Youth Excellent Talent Program (YETP0635), and this study was also partially supported by SB RAS, Grant 28.13. Part of the work was supported by the National Science Council of Taiwan under contract No. NSC 101-2113-M-002-014-MY3.
Предметные рубрики: EMITTING OXYFLUORIDE PHOSPHOR
PHASE-TRANSITIONS
SOLID-STATE
FLUORIDES
DIODES
Аннотация: We present a combined structural analysis on the powder of the Ca2Al3O6F phase using X-ray diffraction (XRD) and Raman spectroscopy techniques. The crystal structure of Ca2Al3O6F has been refined in the rhombohedral system, R space group, a = 17.3237(7) Å, c = 7.00017(4) Å, V = 1819.38(2) Å3, Z = 6. The Ca2Al3O6F phase consists of almost ideal AlO4 tetrahedrons linked through corners, Ca2+ ions in voids, and F− ions disordered over 6 sites around the Ca2 ion. The two different Ca sites have also been verified by the photoluminescence spectrum and decay curves using Eu2+ as the probe ion substituted onto the Ca2+ sites. A lattice dynamics simulation based on the simplified version of the Born–Karman potential model has been produced. Calculated Raman phonon modes agree qualitatively well with the experimental data. The calculations show that the strong line at 538 cm−1 (Ag) corresponds to the vibrational mode of a six-membered AlO4 tetrahedrons ring, and the line at 572 cm−1 (Ag) corresponds to the full symmetric vibration of fluorine atoms in the ab crystal plane.
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6.

Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Molokeev M. S., Misjul S. V., Flerov I. N., Laptash N. M.
Заглавие : Reconstructive phase transition in (NH4)3TiF7 accompanied by the ordering of TiF6 octahedra
Место публикации : Acta Crystallogr. B: Wiley-Blackwell, 2014. - Vol. 70. - P.924-931. - ISSN 0108-7681, DOI 10.1107/S2052520614021192. - ISSN 1600-5740
Примечания : This study was supported by Russian Fund of Basic Research, project No. 12-02-00056 a
Предметные рубрики: CRYSTAL-STRUCTURE
NEUTRON-DIFFRACTION
POWDER DIFFRACTION
FLUORIDES
DISORDER
MECHANISM
PATHWAYS
COMPLEX
LI3THF7
ALPHA
Ключевые слова (''Своб.индексиров.''): reconstructive phase transition--ammonium heptafluorotitanate--order-disorder transition
Аннотация: An unusual phase transition P4/mnc →Pa3 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 1.5-1.8 Å that implies a reconstructive phase transition. It was supposed that phases P4/mbm and Pm3m could be a high-temperature phase and a parent phase, respectively, in (NH4)3TiF7. Therefore, the sequence of phase transitions can be written as Pm3m → P4/bm → P4/mnc → Pa3. The interrelation between (NH4)3TiF7, (NH4)3GeF7 and (NH4)3PbF7 is found, which allows us to suppose phase transitions in relative compounds.
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