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Unusual sequence of phase transitions in (NH4)3TiF7 detected by optic and calorimetric studies / S. V. Mel'nikova [et al.] // J. Fluor. Chem. - 2014. - Vol. 165. - P. 14-19, DOI 10.1016/j.jfluchem.2014.05.016. - Cited References: 13. - This work was supported by Russian Foundation for Basic Research (Grant no. 12-02-00056), 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). . - ISSN 0022-1139. - ISSN 1873-3328

РУБ Chemistry, Inorganic & Nuclear + Chemistry, Organic
Рубрики:
CRYSTAL-STRUCTURE
DIFFRACTION
NH4F
Кл.слова (ненормированные):
Cubic fluorides -- Phase transitions -- Crystal-optic -- Calorimetry
Аннотация: For the first time structural transformations were observed for one of the compounds belonging to the family of double salt fluorides A3MeF7 = A2MeF6·AF. Single crystals of (NH4)3TiF7 = (NH4)2TiF6·NH4F were grown by evaporation of the aqueous solution. Polarizing optical observations, heat capacity and birefringence Δn = (no − ne) measurements were performed in a wide temperature range 100–400 K. Two reversible, first order structural phase transitions were found to be followed by an unusual sequence of symmetry changes: cubic (G3) (T2↓ = 287.5 K; T2↑ = 291–310 K) ↔ P4/mnc (G2) (T1↓ = 358.5 K; T1↑ = 360 K) ↔ 4/m (G1). The twin structures observed were described assuming the existence of cubic parent phase G0 with P m 3 ¯ m symmetry.

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Держатели документа:
RAS, LV Kirensky Phys Inst, Siberian Dept, Krasnoyarsk 660036, Russia
Siberian Fed Univ, Krasnoyarsk 660074, Russia
Russian Acad Sci, Inst Chem, Far Eastern Dept, Vladivostok 690022, Russia

Доп.точки доступа:
Mel'nikova, S. V.; Мельникова, Светлана Владимировна; Pogoreltsev, E. I.; Погорельцев, Евгений Ильич; Flerov, I. N.; Флёров, Игорь Николаевич; Laptash, N. M.; Russian Foundation for Basic Research [12-02-00056]; 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]
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Heat capacity, entropy, dielectric properties and T–p phase diagram of (NH4)3TiF7 / E. I. Pogoreltsev [et al.] // J. Fluor. Chem. - 2014. - Vol. 168. - P. 247-250, DOI 10.1016/j.jfluchem.2014.10.016. - 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). . - ISSN 0022-1139. - ISSN 1873-3328

РУБ Chemistry, Inorganic & Nuclear + Chemistry, Organic
Рубрики:
CRYSTAL-STRUCTURE
   TRANSITIONS
   FLUORIDES
   NH4F
Кл.слова (ненормированные):
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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Держатели документа:
RAS, Siberian Dept, LV Kirensky Phys Inst, Krasnoyarsk 660036, Russia
Siberian Fed Univ, Krasnoyarsk 660074, Russia
Krasnoyarsk State Agr Univ, Krasnoyarsk 660049, Russia
Russian Acad Sci, Far Eastern Dept, Inst Chem, Vladivostok 690022, Russia

Доп.точки доступа:
Pogoreltsev, E. I.; Погорельцев, Евгений Ильич; Flerov, I. N.; Флёров, Игорь Николаевич; Kartashev, A. V.; Карташев, Андрей Васильевич; Bogdanov, E. V.; Богданов, Евгений Витальевич; Laptash, N. M.; 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]
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    Structural transformation between two cubic phases of (NH4)3SnF7 / I. N. Flerov [et al.] // J. Fluor. Chem. - 2015. - Vol. 178. - P. 86-92, DOI 10.1016/j.jfluchem.2015.06.024. - Cited References: 19. - We thank T.A. Kaidalova for the idea of doubling the unit cell parameter of (NH4)3SnF7 at room temperature. The reported study was partially supported by RFBR, research project No. 15-02-02009 a. . - ISSN 0022-1139
   Перевод заглавия: Структурный переход между двумя кубическими фазами в (NH4)3SnF7

РУБ Chemistry, Inorganic & Nuclear + Chemistry, Organic
Рубрики:
CRYSTAL-STRUCTURE
TRANSITION
NH4F
Кл.слова (ненормированные):
Cubic fluorides -- Phase transitions -- X-ray -- Calorimetry -- Crystal optics
Аннотация: Reinvestigations of the room temperature structure of ammonium heptafluorostannate (NH4)3SnF7 = (NH4)2SnF6·NH4F = (NH4)3[SnF6]F by both powder and single crystal X-ray diffractions have revealed that its real symmetry is Pa−3 (Z = 8) instead of Pm−3m (Z = 1) suggested earlier. Polarizing optical observations, heat capacity, X-ray powder, and single crystal measurements were performed in a wide temperature range (100–420 K). A reversible structural phase transition of the first order between two cubic modifications Pa−3 ↔ Pm−3m was found at about T0 = 360 K. The structural models associated with partially disordered and totally ordered high and low temperature phases, respectively, comply with a large value of phase transition entropy.

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Держатели документа:
L.V. Kirensky Institute of Physics, Siberian Branch of RAS, Krasnoyarsk, Russian Federation
Siberian Federal University, Krasnoyarsk, Russian Federation
Far Eastern State Transport University, Khabarovsk, Russian Federation
Institute of Chemistry, Far Eastern Branch of RAS, Vladivostok, Russian Federation

Доп.точки доступа:
Flerov, I. N.; Флёров, Игорь Николаевич; Molokeev, M. S.; Молокеев, Максим Сергеевич; Laptash, N. M.; Udovenko, A. A.; Pogoreltsev, E. I.; Погорельцев, Евгений Ильич; Mel'nikova, S. V.; Мельникова, Светлана Владимировна; Misyul, S. V.; Мисюль, Сергей Валентинович
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    A non-typical sequence of phase transitions in (NH4)3GeF7: optical and structural characterization / S. V. Mel'nikova [et al.] // Dalton Trans. - 2016. - Vol. 45, Is. 12. - P. 5321-5327, DOI 10.1039/c5dt04907e. - Cited References:25. - The reported study was partially supported by RFBR, research project no. 15-02-02009 a . - ISSN 1477-9226. - ISSN 1477-9234
   Перевод заглавия: Необычная последовательность фазовых переходов в (NH4)3GeF7: Оптическое и структурное исследование

РУБ Chemistry, Inorganic & Nuclear
Рубрики:
Crystal-structure
   Powder diffraction
   NH4F
   Fluorination
Аннотация: Single crystals of germanium double salt (NH4)3GeF7 = (NH4)2GeF6·NH4F = (NH4)3[GeF6]F were grown and studied by the methods of polarization optics and X-ray diffraction. The birefringence Δn = (no − ne), the rotation angle of the optical indicatrix ϕ(T) and unit cell parameters were measured in the temperature range 100–400 K. Three structural phase transitions were found at the temperatures: T1↓ = 279.2 K (T1↑ = 279.4 K), T2↑ = 270 K (T2↓ = 268.9 K), T3↓ = 218 K (T3↑ = 227 K). An unusual sequence of symmetry transformations with temperature change was established: P4/mbm (Z = 2) (G1) ↔ Pbam (Z = 4) (G2) ↔ P21/c (Z = 4) (G3) ↔ Pa (Z = 8) (G4). The crystal structures of different phases were determined. The experimental data were additionally interpreted by a group-theoretical analysis of the complete condensate of order parameters taking into account the critical and noncritical atomic displacements. Strengthening of the N–H⋯F hydrogen bonds can be a driving force of the observed phase transitions.

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Держатели документа:
SB RAS, Lab Crystal Phys, Kirensky Inst Phys, Krasnoyarsk 660036, Russia.
Far Eastern State Transport Univ, Dept Phys, Khabarovsk 680021, Russia.
RAS, Inst Chem, Far Eastern Branch, Vladivostok 690022, Russia.
Siberian Fed Univ, Krasnoyarsk 660074, Russia.

Доп.точки доступа:
Mel'nikova, S. V.; Мельникова, Светлана Владимировна; Molokeev, M. S.; Молокеев, Максим Сергеевич; Laptash, N. M.; Misyul, S. V.; Мисюль, Сергей Валентинович; RFBR [15-02-02009 a]
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