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Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Pogoreltsev E. I., Bogdanov E. V., Melnikova S.V., Flerov I. N., Laptash N. M.
Заглавие : (NH4)3HfF7: Crystallooptical and calorimetric studies of a number of successive phase transitions
Место публикации : J. Fluor. Chem.: Elsevier, 2017. - Vol. 204. - P.45-49. - ISSN 00221139 (ISSN), DOI 10.1016/j.jfluchem.2017.10.004
Примечания : Cited References: 14
Аннотация: Single crystals of (NH4)3HfF7 were grown. Polarising optical observations as well as measurement of the heat capacity and birefringence Δn(Т) were performed in the temperature range of 200–310 K. Reversible phase transitions at temperatures T0 = 290 K, Т1 = 280.5 K, Т2 ≈ 273 K, Т3 = 266 K, Т4 = 259 K, Т5 = 231 K, Т6 = 229 K were found. Observations in polarised light make it possible to suggest a sequence of changes in the symmetry groups for these transitions: Fm3m ⟵Т0→ cub. ⟵Т1→ mmm (1) ⟵Т2→ mmm (2) ⟵Т3→ mmm (3) ⟵Т5→ 2/c. The T-p phase diagram was studied and the temperature boundaries of the stability of the distorted crystalline phases were determined. A significant change of the entropy at successive phase transitions ΣΔS = 10.6 J/mol K indicates a disordering of the initial cubic phase.
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Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Bogdanov E. V., Kartashev A. V., Pogoreltsev E. I., Gorev M. V., Laptash N. M., Flerov I. N.
Заглавие : Anomalous behaviour of thermodynamic properties at successive phase transitions in (NH4)3GeF7
Место публикации : J. Solid State Chem. - 2017. - Vol. 256. - P.162-167. - ISSN 00224596 (ISSN), DOI 10.1016/j.jssc.2017.09.010
Примечания : Cited References: 23. - The reported study was partially supported by the Russian Foundation for Basic Research, research project no. 15-02-02009 a.
Ключевые слова (''Своб.индексиров.''): phase transition--fluorides--heat capacity--entropy--thermal expansion--high pressure
Аннотация: Heat capacity, thermal dilatation, susceptibility to hydrostatic pressure and dielectric properties associated with succession of three phase transitions below room temperature in double fluoride salt (NH4)3GeF7 were studied. A possible transformation into the parent Pm-3m cubic phase was not observed up to the decomposition of compound. Nonferroelectric nature of structural distortions was confirmed. The DTA under pressure studies revealed a high temperature stability of two phases: P4/mbm and Pbam. The entropies of the phase transitions agree well with the model of structural distortions. Analysis of the thermal properties associated with the individual phase transitions in the framework of thermodynamic equations has shown a high reliability of the data obtained. © 2017 Elsevier Inc.
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Вид документа : Статья из сборника (однотомник)
Шифр издания :
Автор(ы) : Bogdanov E. V., Pogoreltsev E. I.
Заглавие : Calorimetric study of the fluoro-oxygen crystal (ND4)2MoO2F4
Коллективы : International conference on thermal analysis and calorimetry in Russia, Международная конференция по термическому анализу и калориметрии в России, Институт общей и неорганической химии им. Н.С. Курнакова РАН, Санкт-Петербургский политехнический университет им. Петра Великого
Место публикации : Proc. of int. conf. on therm. analys. and calorim. in Russia (RTAC-2016). - 2016. - Vol. I. - P.181. - ISBN 978-5-7422-5447-8
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Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Abramova G. M., Freydman A. L., Eremin E. V., Pogoreltcev E. I., Velikanov D. A.
Заглавие : Dielectric and magnetic anomalies in α-MnS single crystals at applied magnetic fIelds
Место публикации : J. Supercond. Nov. Magn. - 2022. - Vol. 35, Is. 1. - P.277-281. - ISSN 1557-1939, DOI 10.1007/s10948-021-06045-z. - ISSN 1557-1947(eISSN)
Примечания : Cited References: 22
Предметные рубрики: MAGNETOSTRICTION
ANISOTROPY
Аннотация: Temperature and magnetic field dependences of the magnetic susceptibility and dielectric permittivity of the α-MnS single crystal with NaCl structure are first investigated at around Neel temperature and at 4.2 K and H up to 70 kOe. A relation between the investigated properties was established. The founded phenomena can be due to the magnetostriction or magnetoelastic mechanism and the spin-dependent dipole moment.
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Вид документа : Статья из сборника (однотомник)
Шифр издания :
Автор(ы) : Pogoreltsev E. I., Flerov I. N., Laptash N. M.
Заглавие : Dielectric properties and phase transitions in some oxyfluorides with the MeOxF6-x (x = 1, 2, 3) anion in structure
Коллективы : IEEE International Symposium on Applications of Ferroelectrics, International Meeting on Ferroelectricity
Место публикации : The 12th International Meeting on Ferroelectricity and 18th IEEE International Symposium on Applications of Ferroelectrics (IMF-ISAF 2009): Xi'an, China, August 23-27, 2009 . - 2009
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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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Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Gerasimova Yu. V., Krylov A. S., Vtyurin A. N., Laptash N. M., Pogoreltsev E. I., Dubrovskiy A. A., Gerasimov M. A.
Заглавие : Dynamic processes of the water sublattice in FeTiF6·xH2O·yD2O crystal
Место публикации : J. Raman Spectrosc. - 2022. - Vol. 53, Is. 10: Special Issue: Vibrational Spectroscopy of Water. - P.1704-1709. - ISSN 03770486 (ISSN), DOI 10.1002/jrs.6430
Примечания : Cited References: 31. - The reported study was funded by the Russian Foundation for Basic Research, Government of Krasnoyarsk Territory and Krasnoyarsk Regional Foundation of Science according to the research project “Spectral and magnetic properties of single crystals of transition metal fluoride hexahydrates” No. 20-42-240014
Аннотация: Phase transition in FeTiF6·xH2O·yD2O crystals has been studied by Raman spectroscopy. The 611 cm-1 line corresponding to mode A1g of [TiF6]2- system does not exhibit anomalous behavior associated with the phase transition. The temperature studies showed that below the phase transition temperature, the equivalence of D2O molecules in FeTiF6·xH2O·yD2O octahedron is broken. The phase transition mechanism in the compound under study is associated with Fe(xH2O·yD2O) complex.
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Вид документа : Статья из сборника (однотомник)
Шифр издания :
Автор(ы) : Fokina V. D., Flerov I. N., Molokeev M. S., Pogoreltsev E. I., Bogdanov E. V., Laptev Y. V.
Заглавие : Effect of central cation substitutionon the properties and phase transitions in (NH4)3Me(O2)2F4 oxyfluorides
Коллективы : Воронежский государственный технический университет, Российская академия наук, International Seminar on ferroelastic physics (6; 2009 ; Sept. 22-25; Voronezh), Международный семинар по физике сегнетоэластиков (6(11); 2009 ; 22-25 сент.; Воронеж)
Место публикации : The 6th International Seminar on Ferroelastic Physics: abstract book. - Voronezh, 2009. - P.5
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Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Bogdanov E. V., Pogoreltsev E. I., Gorev M. V., Flerov I. N.
Заглавие : Effect of deuteration on orientational ordering and ferroelastic phase transitions in dioxotetrafluorovanadate (NH4)3VO2F4
Коллективы : International Seminar on Ferroelastic Physics
Место публикации : AOJ Mater. Devices. - 2019. - Vol. 4, Is. 1. - С. 24. - ISSN 2495-3911, DOI 10.23647/ca.md20191506
Примечания : Cited References: 2. - The reported study was funded by Russian Foundation for Basic Research, Government of Krasnoyarsk Territory, Krasnoyarsk Regional Fund of Science to the research project: «Effect of deuterium on orientational ordering and phase transitions in ammonium fluorine oxygen vanadates» № 18-42-243003.
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10.

Вид документа : Статья из сборника (однотомник)
Шифр издания :
Автор(ы) : Bogdanov E. V., Pogoreltsev E. I., Gorev M. V., Flerov I. N.
Заглавие : Effect of deuteration on orientational ordering and ferroelastic phase transitions in dioxotetrafluorovanadate (NH4)3VO2F4
Коллективы : International Seminar on Ferroelastic Physics, Международный семинар по физике сегнетоэластиков, Российская академия наук, Воронежский государственный технический университет
Место публикации : Ninth international seminar on ferroelastic physics (ISFP-9): book of abstracts/ org. com. I. N. Flerov [et al.] ; progr. com. V. I. Zinenko [et al.]. - 2018. - P.25
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11.

Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Bogdanov E. V., Pogoreltsev E. I., Gorev M. V., Molokeev M. S., Flerov I. N.
Заглавие : Effect of Deuteration on Phase Transitions in Vanadium Dioxotetrafluoride
Место публикации : Phys. Solid State. - 2019. - Vol. 61, Is. 2. - P.192-200. - ISSN 10637834 (ISSN), DOI 10.1134/S1063783419020082
Примечания : Cited References: 35. - The reported study was funded by Russian Foundation for Basic Research, Government of Krasnoyarsk Territory, Krasnoyarsk Regional Fund of Science to the research project: "Effect of deuterium on orientational ordering and phase transitions in ammonium fluorine oxygen vanadates," no. 18-42-243003.
Аннотация: The crystals of (ND4)3VO2F4 with a high degree of deuteration (~87%) have been grown and a significant (~1.5%) increase in the unit cell volume has been detected. The decrease in the chemical pressure leads to a change in the sequence of phase transitions due to wedging-out of one of the rhombic phases observed in (NH4)3VO2F4. The thermal physical studies have been carried out and the entropies, deformations, and pressure coefficients related to structural transformations have been determined. The T–p phase diagram has been built and the pressure and temperature boundaries of crystal phase stability have been determined. The dielectric studies demonstrate a nonferroelectric nature of the phase transitions in (ND4)3VO2F4. The experimental and model entropies are compared. Based on the decrease in the entropy as a result of deuteration, a hypothesis on significant but not limited anharmonism of vibrations of ammonia tetrahedral corresponding to the disordering is proposed.
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12.

Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Bogdanov E. V., Pogoreltsev E. I., Gorev M. V., Flerov I. N.
Заглавие : Effect of deuteration on the thermodynamic properties of dioxotetrafluoromolybdate(VI), (NH4)2MoO2F4
Место публикации : Inorg. Chem.: American Chemical Society, 2017. - Vol. 56, Is. 11. - P.6706-6711. - ISSN 00201669 (ISSN), DOI 10.1021/acs.inorgchem.7b00811
Примечания : Cited References: 14. - We are grateful to A. G. Kocharova for preparation of the sample and Dr. A. M. Pugachev for examination of the second harmonic generation. This study was partially supported by the Russian Foundation for Basic Research (Project 16-32-00201mol_a).
Аннотация: Thermal and dielectric studies of (ND4)2MoO2F4 crystals undergoing successive phase transitions at T1 = 272 K and T2 = 181 K showed that deuteration is accompanied by an increase in the chemical pressure in the crystal lattice (Δp ≈ 0.02 GPa), which shifts the Cmcm ↔ Pnma transformation for the first order to the tricritical point. The direct participation of ammonium groups in the mechanism of structural distortions is demonstrated by a decrease in the entropy of the high-temperature phase transition (ΔS1 = R ln 6.0). An external hydrostatic pressure leads to an expansion of the temperature interval of the intermediate antiferroelectric Pnma phase. The triple point on the T–p phase diagram, where the Cmcm, Pnma, amd Pnma* phases coexist, can be realized at a negative pressure of ptrp ≈ −0.8 GPa.
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13.

Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Bogdanov E. V., Pogoreltsev E. I., Gorev M. V., Mel'nikova S. V., Molokeev M. S., Laptash N. M., Flerov I. N.
Заглавие : Effect of the size of the central atom on the stability of crystalline phases in solid solutions (NH4)3TixSn1-xF7
Колич.характеристики :8 с
Место публикации : J. Solid State Chem. - 2023. - Vol. 328. - Ст.124373. - ISSN 00224596 (ISSN), DOI 10.1016/j.jssc.2023.124373. - ISSN 1095726X (eISSN)
Примечания : Cited References: 20. - The study was supported by a grant from the Russian Science Foundation № 23-22-00115, https://rscf.ru/project/23-22-00115/X-ray and dilatometric data and SEM images were obtained using the equipment of the Krasnoyarsk Regional Center for Collective Use of the Federal Research Center — Krasnoyarsk Science Center of the Siberian Branch of the Russian Academy of Sciences. We are grateful to Dr. A.V. Shabanov for examination of the SEM images
Аннотация: The effect of a change in internal pressure as a result of partial substitution of the central atom on the realization and stability of the initial and distorted crystalline phases in (NH4)3TixSn1-xF7 solid solutions has been studied. It was found that at a Ti concentration in the range of x = 0.15–0.40, the reconstructive transition Pm-3m ↔ Pa-3 is transformed into a sequence of phase transitions Pm-3m ↔ P4/mbm ↔ P4/mnc ↔ Pa-3. In the (NH4)3Ti0.15Sn0.85F7 solid solution, the first-order phase transition between two cubic phases at T0 = 352 K is characterized by a significant volume jump δ(ΔV/V0) ≈ 1 %, comparable with that in (NH4)3SnF7. An increase of the Ti concentration leads to a strong decrease in the stability of the Pm-3m cubic phase: the first tetragonal P4/mbm phase appears in (NH4)3Ti0.4Sn0.6F7 at T0 = 400 K, which proves the existence of the predicted high-temperature cubic phase in (NH4)3TiF7. In solid solutions, a decrease in birefringence and entropy of phase transitions was observed in comparison with the initial compounds with Sn and Ti as central atoms. The role of critical parameters (unit cell volume, temperature, external pressure) in the formation of cubic and distorted phases is discussed.
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14.

Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Fokina V. D., Bondarev V. S., Pogoreltsev E. I., Flerov I. N.
Заглавие : Efficiency of energy harvesting and storage using a multilayer capacitor based on BaTi0.86Sn0.14O3 ferroelectric lead-free ceramics
Место публикации : Ceram. Int. - 2022. - Vol. 48, Is. 22. - P.32966-32972. - ISSN 02728842 (ISSN), DOI 10.1016/j.ceramint.2022.07.227
Примечания : Cited References: 45
Аннотация: The study of the parameters of energy harvesting and storage in the lead-free solid solution BaTi0.86Sn0.14O3 (BTSnO) was performed. The permittivity shows the behavior similar to a diffuse phase transition with the critical exponent γ = 1.84, which is close to the value characteristic of relaxors. Large values of the recoverable energy density, Wrec=(5.8–7.0)∙104 J/m3, and the energy storage efficiency coefficient, η=(82–94) %, are implemented in a wide temperature range, 30–87°С, at a low electric field, E = 18.5 kV/cm. For the first time, the analysis of the Olsen cycle was performed using two phase diagrams: polarization – electric field and entropy – temperature. A fairly good agreement was found between the values of the energy conversion density, ND ≈ 0.15 J/cm3, which was determined using two approaches. A universal parameter is proposed for comparing the energy harvesting density for the materials studied in different ranges of temperature and electric fields.
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15.

Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Kazak N. V., Platunov M. S., Knyazev Yu. V., Moshkina E. M., Gavrilkin S. Yu., Bayukov O. A., Gorev M. V., Pogoreltsev E. I., Zeer G. M., Zharkov S. M., Ovchinnikov S. G.
Заглавие : Fe-induced enhancement of antiferromagnetic spin correlations in Mn2−xFexBO4
Место публикации : J. Magn. Magn. Mater. - 2018. - Vol. 452. - P.90-99. - ISSN 03048853 (ISSN), DOI 10.1016/j.jmmm.2017.12.037
Примечания : Cited References: 34. - This study was supported in part by the grants of: The Council for Grants of the President of the Russian Federation (project nos. SP-938.2015.5, NSh-7559.2016.2), the Russian Foundation for Basic Research (project nos. 16-32-60049 mol_a_dk, 16-32-00206 mol_a, 17-02-00826-a, 16-32-50058). The magnetic measurements were carried out in the Shared Facility Centre of P. N. Lebedev Physical Institute of RAS.
Ключевые слова (''Своб.индексиров.''): sro spin correlations--spin-glass--rehac--magnetic frustrations
Аннотация: Fe substitution effect on the magnetic behavior of Mn2−xFexBO4 (x = 0.3, 0.5, 0.7) warwickites has been investigated combining Mössbauer spectroscopy, dc magnetization, ac magnetic susceptibility, and heat capacity measurements. The Fe3+ ions distribution over two crystallographic nonequivalent sites is studied. The Fe introduction breaks a long-range antiferromagnetic order and leads to onset of spin-glass ground state. The antiferromagnetic short-range-order spin correlations persist up to temperatures well above TSG reflecting in increasing deviations from the Curie-Weiss law, the reduced effective magnetic moment and “missing” entropy. The results are interpreted in the terms of the progressive increase of the frustration effect and the formation of spin-correlated regions.
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16.

Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Pogoreltsev E. I., Mel'nikova S. V., Kartashev A. V., Molokeev M. S., Gorev M. V., Flerov I. N., Laptash N. M.
Заглавие : Ferroelastic phase transitions in (NH4)2TaF7
Место публикации : Phys. Sol. St.: Pleiades Publishing, 2013. - Vol. 55, Is. 3. - P.611-618. - DOI 10.1134/S1063783413030232
Аннотация: The heat capacity, unit cell parameters, permittivity, optical properties, and thermal expansion of the (NH4)2TaF7 compound with a seven coordinated anion polyhedron have been measured. It has been found that the compound undergoes two successive phase transitions with the symmetry change: tetragonal (T1 = 174 K) orthorhombic (T2 = 156 K) tetragonal. The ferroelastic nature of structural transformations has been established, and their entropy and susceptibility to hydrostatic pressure have been determined.
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17.

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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18.

Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Fokina V. D., Flerov I. N., Molokeev M. S., Pogoreltsev E. I., Bogdanov E. V., Krylov A. S., Bovina A. F., Voronov V. N., Laptash N. M.
Заглавие : Heat capacity, p-T phase diagram, and structure of Rb2KTiOF5
Коллективы :
Разночтения заглавия :авие SCOPUS: Heat capacity, p-T phase diagram, and structure of Rb2KTiOF 5
Место публикации : Phys. Solid State: MAIK NAUKA/INTERPERIODICA/SPRINGER, 2008. - Vol. 50, Is. 11. - P2175-2183. - ISSN 1063-7834, DOI 10.1134/S1063783408110280
Примечания : Cited References: 23. - This work was supported by the Russian Foundation for Basic Research, project no. 06-02-16102.
Предметные рубрики: ELECTRON-DIFFRACTION
TRANSITIONS
OXYFLUORIDES
(NH4)(2)KWO3F3
TEMPERATURE
XRD
CS
Ключевые слова (''Своб.индексиров.''): 61--50--ks--65--40--ba--65--40--gd--78--30--hv--81--30--dz
Аннотация: Elpasolite Rb2KTiOF5 (space group, Fm was synthesized using a solid-phase reaction method. The temperature dependences of the heat capacity, the unit cell parameters, the structure, the permittivity, the response to an external pressure, and the Raman spectra were studied. A nonferroelectric phase transition was revealed at T (0) = 215 K; the transition is accompanied by a tetragonal distortion of the unit cell (space group I4/m, Z = 10) and a change in the entropy (S (0) = Rln8), which is anomalously large for perovskite-like oxyfluorides with atomic cations. The specific features of the mechanism of structure distortion are discussed in combination with the previous experimental data obtained for cryolite (NH4)(3)TiOF5 and elpasolite Rb2KGaF6.
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19.

Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Flerov I. N., Gorev M. V., Kartashev A. V., Pogorel'tsev E. I., Laptash N. M.
Заглавие : Heat capacity, thermal expansion and barocaloric effect in fluoride K2TaF7
Место публикации : J. Mater. Sci. - 2019. - Vol. 54, Is. 23. - P.14287–14295. - ISSN 00222461 (ISSN), DOI 10.1007/s10853-019-03924-8
Примечания : Cited References: 20. - The reported study was funded by RFBR according to the research Project No. 18-02-00269_a.
Аннотация: The heat capacity and thermal expansion of potassium heptafluorotantalate were studied. The room temperature phase P21/c is stable at least to 4 K. The strong first-order phase transition P21/c−Pnma at T0=486.2K is accompanied by giant changes in the entropy, ΔS0=22.3J(molK)−1, and volume strain, δV0/V=−3.6%. A rather high sensitivity of K2TaF7 to pressure was found, dT0/dp=−220KGPa−1. Significant extensive and intensive barocaloric effects are found at low pressure. The possibility of improving the barocaloric properties is discussed.
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20.

Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Bogdanov E. V., Pogoreltsev E. I., Gorev M. V., Kartashev A. V., Laptash N. M., Flerov I. N.
Заглавие : Heat capacity, thermal expansion and sensitivity to hydrostatic pressure of (NH 4 ) 3 SiF 7 at successive structural phase transitions
Место публикации : J. Solid State Chem. - 2019. - Vol. 276. - P.152-158. - ISSN 00224596 (ISSN) , DOI 10.1016/j.jssc.2019.04.029
Примечания : Cited References: 20
Аннотация: Heat capacity, thermal dilatation, permittivity and sensitivity to external pressure of (NH4)3SiF 7 were studied. Due to the absence of cubic phases Pm3¯m and Pa3¯, a strong decrease in the total entropy change ∑ΔSi =19 J/mol K associated with four successive transformations P4/mbm↔Pbam↔P2 1 /c11↔P1¯↔P12 1 /c1 was found in silicate in comparison with other double fluoride salts (NH4)3MeF7 (Me: Ge, Ti, Sn) Using analysis of the excess heat capacity in the framework of the thermodynamic theory, the entropies associated with each individual phase transition were determined. In accordance with the entropic parameters, the complete ordering of the structural elements occurs in the monoclinic phase P21/c11. Further change in symmetry is associated with small entropy changes which prove insignificant displacement of structural units. A T−p phase diagram was constructed and good agreement was found between measured and calculated baric coefficients. © 2019 Elsevier Inc.
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