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Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Mel'nikova S. V., Pogoreltsev E. I., Flerov I. N., Laptash N. M.
Заглавие : Unusual sequence of phase transitions in (NH4)3TiF7 detected by optic and calorimetric studies
Коллективы : 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]
Место публикации : J. Fluor. Chem.: Elsevier Science, 2014. - Vol. 165. - P.14-19. - ISSN 0022-1139, DOI 10.1016/j.jfluchem.2014.05.016. - ISSN 1873-3328
Примечания : 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).
Предметные рубрики: CRYSTAL-STRUCTURE
DIFFRACTION
NH4F
Ключевые слова (''Своб.индексиров.''): 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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Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Flerov I. N., Kartashev A. V., Gorev M. V., Bogdanov E. V., Mel'nikova S. V., Molokeev M. S., Pogoreltsev E. I., Laptash N. M.
Заглавие : Thermal, structural, optical, dielectric and barocaloric properties at ferroelastic phase transition in trigonal (NH4)2SnF6: A new look at the old compound
Место публикации : J. Fluor. Chem.: Elsevier, 2016. - Vol. 183. - P.1-9. - ISSN 00221139 (ISSN), DOI 10.1016/j.jfluchem.2015.12.010
Примечания : Cited References: 25. - The reported study was partially supported by RFBR, research project No. 15-02-02009a.
Предметные рубрики: Heat-capacity
Ammonium
(NH4)3TiF7
Pressure
Ключевые слова (''Своб.индексиров.''): fluorides--structural disorder--phase transitions--entropy--barocaloric effect
Аннотация: Structural phase transition P-3m1 → P-1 of the first order and nonferroelectric nature was found in (NH4)2SnF6 at about 110 K in the process of thermal, optical, dielectric and X-ray studies. Order-disorder transformation is accompanied by large changes of entropy (ΔS0 = 16.4 J/mol K) and volume (ΔV0/V ≈ 1%). The structural model associated with three orientations of NH4 tetrahedra in P-3m1 phase and their complete ordering in P-1 phase was suggested with the entropy change (ΔS0 = 18.3 J/mol K) close to the experimental value. A good agreement between baric coefficients measured in a direct way (dT0/dp = -157 K/GPa) and evaluated using entropy and volume changes at phase transition (-170 K/GPa) was found. Barocaloric effects in (NH4)2SnF6 are comparable with those of known solid state refrigerants and are characterised by a low-pressure need for realising their maximum values. © 2015 Elsevier B.V. All rights reserved.
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Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Fokina V. D., Gorev M. V., Bogdanov E. V., Pogoreltsev E. I., Flerov I. N., Laptash N. M.
Заглавие : Thermal properties and phase transitions in (NH4) 3ZrF7
Место публикации : Journal of Fluorine Chemistry. - 2013. - Vol. 154. - P.1-6. - ISSN 0022-1139, DOI 10.1016/j.jfluchem.2013.07.001
Ключевые слова (''Своб.индексиров.''): cubic fluorides--entropy--permittivity--phase transitions--pressure effect--thermal dilatation
Аннотация: The heat capacity, thermal dilatation, permittivity, and T-p phase diagram of (NH4)3ZrF7 have been studied in wide temperature and pressure ranges. Two phase transitions were found in addition to previously known structural transformations. The stability of crystal phases to temperature and pressure has been examined and a possibility of transition between two cubic phases has been discussed. The total excess entropy change SDSi = Rln6 is characteristic for the order-disorder processes, but its stepwise increase is not consistent with the structural model associated with the strong disorder assumed in the initial cubic phase. В© 2013 Elsevier B.V. All rights reserved.
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Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Boca M., Molokeev M. S., Rakhmatullin A., Kubikova B., Netriova Z.
Заглавие : The structure of the metastable K18Ta5Zr5F63 phase
Место публикации : New J. Chem. - 2020. - Vol. 44, Is. 22. - P.9264-9270. - ISSN 11440546 (ISSN), DOI 10.1039/d0nj02428g
Примечания : Cited References: 30. - Financial support from TGIR-RMN-THC Fr3050 CNRS for conducting the research is gratefully acknowledged. This work was supported by the Slovak Research and Development Agency under the contract no. APVV-15-0479. This work was financially supported by the Scientific Grant Agency of the Ministry of Education of the Slovak Republic and the Slovak Academy of Sciences, grant no. Vega 2/0024/20
Аннотация: A metastable phase K18Ta5Zr5F63 was prepared by molten salt synthesis of K2TaF7 and K2ZrF6 in a sealed Pt crucible. This is the first example of a structure of a fluoride complex compound containing both tantalum and zirconium as central atoms. The asymmetric part of the unit cell contains two Ta/Zr sites and one pure Zr site. The Ta1/Zr1 ion is coordinated by seven F ions forming one capped trigonal prism. The Ta2/Zr2 ion is coordinated by six F ions forming a trigonal prism, and this polyhedron is fully ordered. The Zr3 ion is coordinated by six F ions, which are disordered over two positions. All (Zr/Ta)Fn (n = 6–8) polyhedra are isolated from each other, although the ZrF6 units have shared faces, forming an infinite channel along the c-axis. 19F MAS NMR experiments agree with the proposed structural model, identifying all five central non-equivalent polyhedra. The K18Ta5Zr5F63 phase decomposes within several months to its initial components; this can be monitored by NMR, DSC and XRD experiments. Moreover, accelerated decomposition can be achieved by thermal treatment, resulting in the formation of a K3ZrF7 phase.
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Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Atuchin V. V., Molokeev M. S., Yurkin G. Yu., Gavrilova T. A., Kesler V. G., Laptash N. M., Flerov I. N., Patrin G. S.
Заглавие : Synthesis, structural, magnetic, and electronic properties of cubic CsMnMoO3F3 oxyfluoride
Место публикации : J. Phys. Chem. C: American Chemical Society, 2012. - Vol. 116, Is. 18. - P.10162-10170. - ISSN 1932-7447, DOI 10.1021/jp302020f
Примечания : Cited References: 64. - We thank Dr. A.M. Ziatdinov for the electron paramagnetic resonance measurements. This study was partly supported by SB RAS (Grant 28).
Предметные рубрики: RAY PHOTOELECTRON-SPECTROSCOPY
PHASE-TRANSITIONS
CORE LEVELS
SURFACE CHARACTERIZATION
CRYSTAL-STRUCTURE
CLEAVED SURFACE
MIXED-VALENCE
OXIDES
MN
MOLYBDENUM
Chemical bondings
Cubic phase
Energy differences
Heat capacity measurements
Oxyfluorides
Powder samples
Solid-state synthesis
Space Groups
Temperature range
Valence electron
Binding energy
Chemical bonds
Electronic structure
Fluorine compounds
Magnetic properties
Metal ions
Photoelectrons
Rietveld method
X ray photoelectron spectroscopy
Electronic properties
Аннотация: A powder sample of CsMnMoO3F3 oxyfluoride has been prepared by solid state synthesis. The pyrochlore-related crystal structure of CsMnMoO3F3 has been refined by the Rietveld method at T = 298 K (space group Fd-3m, a = 10.59141(4) angstrom, V = 1188.123(8) angstrom(3); R-B = 3.44%). The stability of the cubic phase has been obtained over the temperature range T = 110-293 K by heat capacity measurements. Magnetic properties have been measured over the range of T = 2-300 K. The electronic structure of CsMnMoO3F3 has been evaluated by X-ray photoelectron spectroscopy. Chemical bonding effects have been discussed for all metal ions using binding energy difference parameters and wide comparison with related oxides and fluorides. The competition between O-2(-) and F- ions for metal valence electrons has been found.
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Вид документа : Статья из сборника (однотомник)
Шифр издания :
Автор(ы) : Flerov I. N., Pogoreltsev E. I., Mel'nikova S. V., Gorev M. V., Kartashev A. V., Bogdanov E. V., Molokeev M. S., Laptash N. M.
Заглавие : Structure, physical properties and phase transitions in (NH4)2TiF6×NH4F
Коллективы : European Symposium on Fluorine Chemistry (17; 2013 ; June ; 21-25; Paris, France)
Место публикации : 17th European Symposium on Fluorine Chemistry: Abstracts book. - 2013. - P.37
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Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Flerov I. N., Molokeev M. S., Laptash N. M., Udovenko A. A., Pogoreltsev E. I., Mel'nikova S. V., Misyul S. V.
Заглавие : Structural transformation between two cubic phases of (NH4)3SnF7
Место публикации : J. Fluor. Chem.: Elsevier, 2015. - Vol. 178. - P.86-92. - ISSN 0022-1139, DOI 10.1016/j.jfluchem.2015.06.024
Примечания : 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.
Предметные рубрики: CRYSTAL-STRUCTURE
TRANSITION
NH4F
Ключевые слова (''Своб.индексиров.''): 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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Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Gorev M. V., Flerov I. N., Tressaud A., Molokeev M. S., Kartashev A. V., Pogoreltsev E. I., Bayukov O. A.
Заглавие : Phase transitions in fluoride KFe2F6 with tetragonal tungsten bronze structure
Коллективы : RFBR [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]
Место публикации : J. Fluor. Chem.: Elsevier Science, 2014. - Vol. 168. - P.204-211. - ISSN 0022-1139, DOI 10.1016/j.jfluchem.2014.09.031. - ISSN 1873-3328
Примечания : Cited References: 14. - This work was supported by RFBR, project 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 NSh-924.2014.2).
Предметные рубрики: K3FE5F15
490-K
ORDER
Ключевые слова (''Своб.индексиров.''): tetragonal tungsten bronze structure--phase transition--charge ordering--thermal properties
Аннотация: Heat capacity, thermal dilatation, structure, Mossbauer spectra and dielectric permittivity of fluoride KFe2F6 with tetragonal tungsten bronze crystal structure were studied. The as-made sample undergoes two structural phase transitions P4/mbm (T-1 approximate to 340 K) - Pbam (T-2 approximate to 250 K) - G(2) and magnetic phase transformation at T-m approximate to 133 K. Heating up to 600-700 K and subsequent cooling in helium atmosphere leads to a change of phase transition temperatures and diffused anomalies in thermal expansion. The results obtained and influence of thermal prehistory of the sample on its physical properties are discussed in the context of previous studies on related fluorides KFe2F6, which sometimes suggest conflicting structural details. (C) 2014 Elsevier B.V. All rights reserved.
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Вид документа : Статья из сборника (однотомник)
Шифр издания :
Автор(ы) : Molokeev M. S., Bogdanov E. V., Misyul S. V., Tressaud A., Flerov I. N.
Заглавие : Phase transitions in defect pyrochlore structure of CsFe2F6
Коллективы : European Symposium on Fluorine Chemistry (17; 2013 ; June ; 21-25; Paris, France)
Место публикации : 17th European Symposium on Fluorine Chemistry: Abstracts book. - 2013. - P.276
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10.

Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Bogdanov E. V., Molokeev M. S., Gorev M. V., Kartashev A. V., Laptash N. M., Flerov I. N.
Заглавие : Phase transition in RbCdZrF7: Structure and thermal properties
Место публикации : J. Fluor. Chem. - 2021. - Vol. 245. - Ст.109748. - ISSN 00221139 (ISSN), DOI 10.1016/j.jfluchem.2021.109748
Примечания : Cited References: 30. - The reported study was funded by RFBR according to the research project No. 18-02-00269 a. X-ray and dilatometric data were obtained using the equipment of Krasnoyarsk Regional Center of Research Equipment of Federal Research Center "Krasnoyarsk Science Center SB RAS"
Аннотация: X-ray, calorimetric and dilatometric studies of RbCdZrF7 revealed the existence of the second order phase transition Cmcm - P21/m at T0 = 200 K. The structure of the initial and distorted phases is ordered. The phase transition is associated with displacements of fluorine atoms, which leads to minor rotations of the CdF7 and ZrF7 pentagonal bipyramids. A small change in entropy, 0.1R, is characteristic of displacive-type transformations. An anomalously high susceptibility of the transition temperature to hydrostatic pressure was found.
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