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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) : 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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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) : Kartashev A. V., Gorev M. V., Bogdanov E. V., Flerov I. N., Laptash N. M.
Заглавие : Thermal properties and phase transition in the fluoride, (NH4)3SnF7
Место публикации : J. Solid State Chem. - 2016. - Vol. 237. - P.269-273. - ISSN 00224596 (ISSN), DOI 10.1016/j.jssc.2016.02.027
Примечания : Cited References: 18. - This study was partially supported by the Russian Foundation for Basic Research (RFBR), research Project no. 15-02-02009a.
Предметные рубрики: Heat-capacity
Chemistry
Ключевые слова (''Своб.индексиров.''): phase transition--fluorides--heat capacity--entropy--thermal expansion--high pressure
Аннотация: Calorimetric, dilatometric and differential thermal analysis studies were performed on (NH4)3SnF7 for a wide range of temperatures and pressures. Large entropy (δS0=22 J/mol K) and elastic deformation (δ(ΔV/V)0=0.89%) jumps have proven that the Pa-3虠Pm-3m phase transition is a strong first order structural transformation. A total entropy change of ΔS0=32.5 J/mol K is characteristic for the order-disorder phase transition, and is equal to the sum of entropy changes in the related material, (NH4)3TiF7, undergoing transformation between the two cubic phases through the intermediate phases. Hydrostatic pressure decreases the stability of the high temperature Pm-3m phase in (NH4)3SnF7, contrary to (NH4)3TiF7, characterised by a negative baric coefficient. The effect of experimental conditions on the chemical stability of (NH4)3SnF7 was observed. © 2016 Elsevier Inc.
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Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Volkov N. V., Sablina K. A., Eremin E. V., Boni P., Shah V. R., Flerov I. N., Kartashev A., Rasch JCE, Boehm M., Schefer J.
Заглавие : Heat capacity of a mixed-valence manganese oxide Pb(3)Mn(7)O(15)
Коллективы :
Разночтения заглавия :авие SCOPUS: Heat capacity of a mixed-valence manganese oxide Pb3Mn 7O15
Место публикации : J. Phys.: Condens. Matter: IOP PUBLISHING LTD, 2008. - Vol. 20, Is. 44. - Ст.445214. - ISSN 0953-8984, DOI 10.1088/0953-8984/20/44/445214
Примечания : Cited References: 11. - This study was supported by the INTAS (project No 061000013-9002), the Division of Physical Sciences of RAS, program `Spin-dependent Effects in Solids and Spintronics' (project No. 2.4.2 of SB RAS), the President of the Russian Federation, grant for Support of Leading Scientific Schools (project No. NSh-1011.2008.2), KRSF-RFBR `Enisey2007', project No. 07-02-96801-a, and the Siberian Branch of RAS, Integration project No. 3.7.
Ключевые слова (''Своб.индексиров.''): antiferromagnetism--crystallography--entropy--lead alloys--magnetic materials--magnetism--manganese--manganese compounds--powders--single crystals--specific heat--spin dynamics--antiferromagnetic orders--charge localizations--entropy losses--excess heat capacities--experimental datums--heat capacities--magnetic contributions--magnetic orders--magnetic states--magnetic subsystems--magnetic transitions--manganese oxides--nonmagnetic--spin systems--temperature curves--temperature dependences--temperature intervals--temperature ranges--manganese alloys
Аннотация: We present the results of a heat capacity study of Pb(3)Mn(7)O(15) single crystals with approximately equal concentrations of Mn(3+) and Mn(4+) ions. In the temperature interval between 210 and 260 K, an excess heat capacity of nonmagnetic origin, most likely associated with the process of charge localization, has been observed. Also, three pronounced anomalies corresponding to the changes in a magnetic subsystem of the crystal have been observed in the temperature dependence of the heat capacity. A broad hump near 150 K is related to the formation of a short-range magnetic order. This process of short-range ordering is rather prominent, considering the appreciable value of the entropy loss accompanying the change in the magnetic state. A clear lambda-shaped peak at 70 K marks the onset of a long-range antiferromagnetic order. Another anomalous contribution to the heat capacity of magnetic origin has been revealed at temperatures below 20 K. This contribution is associated with a magnetic transition of an unknown nature, which is also clearly evident in magnetization versus temperature curves. The total magnetic contribution to the entropy deduced from the actual experimental data over the entire temperature range is much smaller than is expected for a completely ordered Mn spin system in the crystal. We suggest several possible reasons that may account for this `missing' entropy.
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Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Gorban A., Popova T., Zinovyev A.
Заглавие : Codon usage trajectories and 7-cluster structure of 143 complete bacterial genornic sequences
Разночтения заглавия :авие SCOPUS: Codon usage trajectories and 7-cluster structure of 143 complete bacterial genomic sequences
Место публикации : Physica A: ELSEVIER SCIENCE BV, 2005. - Vol. 353. - P365-387. - ISSN 0378-4371, DOI 10.1016/j.physa.2005.01.043
Примечания : Cited References: 46
Предметные рубрики: DNA-BASE COMPOSITION
ASYMMETRIC SUBSTITUTION PATTERNS
PROTEIN-CODING REGIONS
MICROBIAL GENOMES
GENE IDENTIFICATION
MARKOV-MODELS
G+C CONTENT
BIAS
PREDICTION
SELECTION
Ключевые слова (''Своб.индексиров.''): genome--cluster--codon usage--correlations--entropy--mean field--cluster--codon usage--correlations--entropy--genome--mean field--approximation theory--correlation methods--database systems--entropy--functions--genes--mathematical models--clusters--codon usage--genomes--mean field--bacteria
Аннотация: Three results are presented. First, we prove the existence of a universal 7-cluster structure in all 143 completely sequenced bacterial genomes available in Genbank in August 2004, and explained its properties. The 7-cluster structure is responsible for the main part of sequence heterogeneity in bacterial genomes. In this sense, our 7 clusters is the basic model of bacterial genome sequence. We demonstrated that there are four basic "pure" types of this model, observed in nature: "parallel triangles", "perpendicular triangles", degenerated case and the flower-like type. Second, we answered the question: how big are the position-specific information and the contribution connected with correlations between nucleotide. The accuracy of the mean-field (context-free) approximation is estimated for bacterial genomes. We show that codon us-age of bacterial genomes is a multi-linear function of their genomic G+C-content with high accuracy (more precisely, by two similar functions, one for eubacterial genomes and the other one for archaea). Description of these two codon-usage trajectories is the third result. All 143 cluster animated 3D-scatters are collected in a database and is made available on our web-site: http://www.ihes.fr/similar to zinovyev/7clusters. (c) 2005 Elsevier B.V. All rights reserved.
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Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Gorev M. V., Flerov I. N., Tressaud A., Durand E.
Заглавие : The p-T phase diagram of ammonium hexafluoroaluminate
Место публикации : J. Phys.: Condens. Matter: IOP PUBLISHING LTD, 2002. - Vol. 14, Is. 25. - P6447-6453. - ISSN 0953-8984, DOI 10.1088/0953-8984/14/25/312
Примечания : Cited References: 17
Предметные рубрики: NUCLEAR MAGNETIC-RESONANCE
TRANSITIONS
MOTIONS
F-19
H-1
Ключевые слова (''Своб.индексиров.''): entropy--hydrostatic pressing--mathematical models--order disorder transitions--phase diagrams--specific heat of solids--ammonium hexafluoroaluminate--crolite--elpasolite--ammonium compounds
Аннотация: The heat capacity and the effect of hydrostatic pressure on structural phase transitions in ammonium hexafluoroaluminate, (NH4)(3)AlF6, have been studied. Two heat capacity anomalies have been found with maxima at T-1 = 218.5 +/- 0.5 K and T-2 = 179 +/- 2 K. Respective entropy changes of phase transitions are DeltaS(1) = 15.3 +/- 0.5 J mol(-1) K-1 and DeltaS(2) = 2.5 +/- 0.5 J mol(-1) K-1. It is shown that the p-T phase diagram of this compound is rather complex and contains a triple point (p(tp) = 0.12 GPa, T-tp = 221 K) and high-pressure phase. The mechanism of transformations and generalized p-T phase diagram for compounds of the (NH4)(3)(MF6)-F-III family are discussed within the framework of the rotational order-disorder model.
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Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Flerov I. N., Gorev M. V.
Заглавие : Entropy and the mechanism of phase transitions in elpasolites
Место публикации : Phys. Solid State: AMER INST PHYSICS, 2001. - Vol. 43, Is. 1. - P127-136. - ISSN 1063-7834, DOI 10.1134/1.1340198
Примечания : Cited References: 33
Предметные рубрики: ORDERED PEROVSKITE PB2MGTEO6
ELASTIC NEUTRON-DIFFRACTION
THERMODYNAMIC PROPERTIES
CUBIC PEROVSKITES
CRYSTAL-STRUCTURE
HIGH-RESOLUTION
PB2MGWO6
CSPBCL3
Аннотация: The phase transitions in series of crystals with the general formulas A(2)BB'X-6 (X = F, Cl, Br, or CN) and Pb2BB'O-6 that belong to the elpasolite family (space group Fm(3) over bar m) are analyzed. The influence of the size and the shape of cations and anions on the entropy and the mechanism of structural distortions is discussed. (C) 2001 MAIK "Nauka/Interperiodica".
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Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Vasiliev A. N., Popova E. A., Bezmaternykh L. N., Temerov V. L., Hiroi Z.
Заглавие : Specific heat of YFe3(BO3)(4), Y0.5Gd0.5Fe3(BO3)(4), and GdFe3(BO3)(4)
Разночтения заглавия :авие SCOPUS: Specific heat of YFe3(BO3)4, Y 0.5Gd0.5Fe3(BO3)4, and GdFe3(BO3)4
Место публикации : J. Exp. Theor. Phys.: MAIK NAUKA/INTERPERIODICA/SPRINGER, 2006. - Vol. 102, Is. 2. - P262-265. - ISSN 1063-7761, DOI 10.1134/S1063776106020075
Примечания : Cited References: 10
Предметные рубрики: TRIGONAL GDFE3(BO3)(4)
Ключевые слова (''Своб.индексиров.''): antiferromagnetism--gadolinium compounds--heat transfer--ions--magnetic fields--single crystals--temperature measurement--yttrium compounds--magnetic entropy--magnetic system--reorientational transitions--scaling procedure--specific heat of solids
Аннотация: The specific heat was measured in the range 0.4-300 K in YFe3(BO3)(4), Y0.5Gd0.5Fe3(BO3)(4), and GdFe3(BO3)(4) single crystals. Sharp anomalies were found at temperatures of first-order structural, second-order antiferromagnetic, and first-order spin-reorientational transitions. A Neel temperature of about 37 K was found to be virtually independent of presence of rare-earth ions, indicating rather weak coupling of Gd and Fe subsystems. The contribution of the magnetic system to specific heat was separated through the scaling procedure allowing determination of the magnetic entropy of Fe and Gd subsystems. At the lowest temperatures, the specific heat in GdFe3(BO3)(4) exhibits a Schottky-type anomaly, which is due to Gd3+ eightfold degenerate ground-level splitting by the internal magnetic field of the Fe subsystem of about 7 T.
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10.

Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Flerov I. N., Gorev M. V., Voronov V. N.
Заглавие : Entropy of Rb2KB3+F6 (B3+: Se, In, Lu, Er, Ho) ferroelastics and the triple point on T(R(B)(3+)) diagram
Место публикации : Fiz. Tverd. Tela: MEZHDUNARODNAYA KNIGA, 1996. - Vol. 38, Is. 3. - P717-727. - ISSN 0367-3294
Примечания : Cited References: 26
Предметные рубрики: STRUCTURAL PHASE-TRANSITIONS
RB2KMIIIF6 ELPASOLITES
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11.

Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Pogoreltsev E. I., Bogdanov E. V., Kartashev A. V., Molokeev M. S., Flerov I. N., Laptash N. M.
Заглавие : Thermal properties of (NH4)2MeF6·NH4F (Me: Ti, Sn) crystals undergoing transformation between two cubic phases
Место публикации : Ferroelectrics: Taylor and Francis, 2016. - Vol. 501, Is. 1. - P.20-25. - ISSN 00150193 (ISSN), DOI 10.1080/00150193.2016.1198659
Примечания : Cited References: 9. - The reported study was partially supported by RFBR, research project No 15-02-02009-a
Ключевые слова (''Своб.индексиров.''): phase transitions--fluorides--heat capacity--entropy--phase diagram
Аннотация: The heat capacity, thermal expansion, and T-p phase diagrams of (NH4)3TiF7 and (NH4)3SnF7 were studied in wide temperature and pressure ranges. The total excess entropies at successive Pa-3 ↔ P4/mnc ↔ 4/m (Ti) and single Pa-3 ↔ Pm-3m (Sn) phase transitions are close to each other and characteristic for the order–disorder processes. The Pm-3m cubic phase and direct Pa-3 ↔ Pm-3m transformation were found at high pressure in (NH4)3TiF7. The different sign of baric coefficients for phase transition between two cubic phases in (NH4)3TiF7 and (NH4)3SnF7 was supposed due to nonlinear phase boundary with pressure in the latter fluoride.
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12.

Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Mikhaleva E. A., Flerov I. N., Kartashev A. V., Gorev M. V., Bogdanov E. V., Bondarev V. S.
Заглавие : Thermal, dielectric and barocaloric properties of NH4HSO4 crystallized from an aqueous solution and the melt
Место публикации : Solid State Sci.: Elsevier, 2017. - Vol. 67. - P.1-7. - ISSN 12932558 (ISSN), DOI 10.1016/j.solidstatesciences.2017.03.004
Примечания : Cited References: 27. - We are grateful to T.N. Davydova for the preparation of the sample from an aqueous solution and Dr. M.S. Molokeev for X-ray characterization of the samples. The study was partially supported by the Russian Foundation for Basic Research, research project No. 16-32-00092 mol_а.
Ключевые слова (''Своб.индексиров.''): entropy--ferroelectric--phase diagram--phase transition--thermal and dielectric properties
Аннотация: A study of heat capacity, thermal dilatation, permittivity, dielectric loops and susceptibility to hydrostatic pressure was carried out on quasi-ceramic samples of NH4HSO4 obtained from an aqueous solution as well as the melt. The main parameters of the successive P21/c (T1) ↔ Pc (T2) ↔ P1 phase transitions did not depend on the method of preparation of the samples, and were close to those determined in previous studies of single crystal and powder, except for the sign and magnitude of the baric coefficient for T2. Direct measurements of the pressure effect on the permittivity and thermal properties showed dT2/dp = −123 K·GPa−1, which is consistent in terms of magnitude and sign with the baric coefficient evaluated using dilatometric and calorimetric data in the framework of the Clausius-Clapeyron equation. Thus, the temperature region of the ferroelectric Pc phase existence is extended under pressure. A strong decrease in the entropy jump at the Pc ↔ P1 transformation with an increase in pressure, and the linear dependence of T2 on pressure, indicate that an increase in pressure shifts this phase transition towards the tricritical point on the T–p phase diagram. A significant barocaloric effect was found in the region of the Pc ↔ P1 phase transition.
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13.

Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Zinenko V. I., Pavlovskii M. S.
Заглавие : Thermodynamics of spin ice in staggered and direct (along the [111] axis) fields in the cluster approximation
Коллективы : Russian Foundation for Basic Research; Government of the Krasnoyarsk Territory; Krasnoyarsk Territory Foundation for Supporting the Scientific and Research Activity [16-42-243039]
Место публикации : J. Exp. Theor. Phys.: MAIK Nauka-Interperiodica / Springer, 2017. - Vol. 124, Is. 2. - P.295-303. - ISSN 1063-7761, DOI 10.1134/S1063776117020182. - ISSN 1090-6509(eISSN)
Примечания : Cited References:15. - This work was supported by the Russian Foundation for Basic Research, the Government of the Krasnoyarsk Territory, and the Krasnoyarsk Territory Foundation for Supporting the Scientific and Research Activity (project no. 16-42-243039).
Предметные рубрики: ENTROPY
HEAT
Аннотация: We have analyzed the low-temperature thermodynamic properties of spin ice in the staggered and direct (acting along the [111] axis) fields for rare-earth oxides with the chalcolamprite structure and general formula Re23+Me24+O72- . Calculations have been performed in the cluster approximation. The results have been compared with experimental temperature dependences of heat capacity and entropy for Dy2Ti2O7 compound for different values of the external field in the [111] direction. The experimental data and calculated results have also been compared for the Pr2Ru2O7 compound with the antiferromagnetic ordering of magnetic moments of ruthenium ions, which gives rise to the staggered field acting on the system of rare-earth ions. The calculated temperature dependences of heat capacity and entropy are in good agreement with experimental data.
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14.

Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Gorev M. V., Bogdanov E. V., Flerov I. N.
Заглавие : Conventional and inverse barocaloric effects around triple points in ferroelastics (NH4)3NbOF6 and (NH4)3TiOF5
Место публикации : Scripta Mater. - 2017. - Vol. 139. - P.53-57. - ISSN 13596462 (ISSN), DOI 10.1016/j.scriptamat.2017.06.022
Примечания : Cited References: 17
Ключевые слова (''Своб.индексиров.''): barocaloric effect--entropy--order-disorder phenomena--phase diagram--polymorphic phase transformation
Аннотация: We report the conventional and inverse barocaloric effect (BCE) in ferroelastics (NH4)3NbOF6 and (NH4)3TiOF5. We found a rich set of the structural phase transitions and triple points on the T − p phase diagrams. Extensive and intensive BCE near some transformations and around triple points in both crystals are outstanding (|∆ SBCE max | = 30–100 J/kg·K; |∆ TAD max | = 4–22 K) and can be achieved at low pressure 0.01–0.60 GPa.
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15.

Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Gorev M. V., Bogdanov E. V., Flerov I. N.
Заглавие : T-p phase diagrams and the barocaloric effect in materials with successive phase transitions
Коллективы : Russian Foundation for Basic Research, Government of Krasnoyarsk Territory, Krasnoyarsk Region Science and Technology Support Fund [17-42-240076 p-a]
Место публикации : J. Phys. D: IOP Publishing, 2017. - Vol. 50, Is. 38. - Ст.384002. - ISSN 0022-3727, DOI 10.1088/1361-6463/aa8025. - ISSN 1361-6463(eISSN)
Примечания : Cited References:51. - The reported study was funded by Russian Foundation for Basic Research, Government of Krasnoyarsk Territory, Krasnoyarsk Region Science and Technology Support Fund to the research project no. 17-42-240076 p-a.
Предметные рубрики: SOLID-STATE REFRIGERATION
ELECTROCALORIC REFRIGERATION
MAGNETIC
Ключевые слова (''Своб.индексиров.''): barocaloric effect--phase transition--phase diagram--entropy
Аннотация: An analysis of the extensive and intensive barocaloric effect (BCE) at successive structural phase transitions in some complex fluorides and oxyfluorides was performed. The high sensitivity of these compounds to a change in the chemical pressure allows one to vary the succession and parameters of the transformations (temperature, entropy, baric coefficient) over a wide range and obtain optimal values of the BCE. A comparison of different types of schematic T-p phase diagrams with the complicated dependences observed experimentally shows that in some ranges of temperature and pressure the BCE in compounds undergoing successive transformations can be increased due to a summation of caloric effects associated with distinct phase transitions. The maximum values of the extensive and intensive BCE in complex fluorides and oxyfluorides can be realized at rather low pressure (0.1-0.3 GPa). In a narrow temperature range around the triple points conversion from conventional BCE to inverse BCE is observed, which is followed by a gigantic change of both |ΔSBCE| and |ΔTAD|.
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16.

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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17.

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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18.

Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Mel'nikova S. V., Bogdanov E. V., Molokeev M. S., Laptash N. M., Flerov I. N.
Заглавие : Optical and calorimetric studies of K2TaF7
Место публикации : J. Fluor. Chem. - 2019. - Vol. 222-223. - P.75-80. - ISSN 00221139 (ISSN) , DOI 10.1016/j.jfluchem.2019.04.016
Примечания : Cited References: 26. - The reported study was funded by RFBR according to the research project № 18-02-00269.
Аннотация: Optical and calorimetric experiments on K2TaF7 are performed in a wide temperature range. No features were found in the behavior of the birefringence Δnb(T), the angle of rotation of the indicatrix ϕ(T) and the heat capacity ΔCp(T) except for those associated with the Pnma↔P21/c phase transition. Structural transformation was characterized as strong first order “proper” ferroelastic accompanied by a huge angle ϕ ≈40° and strong pre-transition phenomena in Δnb(T). Two contributions to the anomalies of the optical properties were found associated with the photoelastic effect and the transition parameter related linearly to the spontaneous deformation. Thermal treatments cause correlated changes in temperature and enthalpy of the phase transition, which leads to the invariance of the large magnitude of the corresponding entropy ΔS = 22 J/mol·K which does not match the model with the absence of structural disorder in the Pnma phase.
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19.

Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Pogoreltsev E. I., Mel'nikova S. V., Molokeev M. S., Flerov I. N., Laptash N. M.
Заглавие : Structural, thermal and optical properties of elpasolite-like (NH4)2KZrF7
Место публикации : J. Solid State Chem. - 2019. - Vol. 277. - P.376-380. - ISSN 00224596 (ISSN), DOI 10.1016/j.jssc.2019.06.013
Примечания : Cited References: 28. - The reported study was funded by RFBR according to the research project No. 18-02-00269 a . The authors are grateful to Krasnoyarsk Center of collective use of SB RAS for providing X-ray analytical equipment.
Аннотация: New fluoride compound (NH4)2KZrF7 with the elpasolite structure (sp. gr. Fm-3m) was synthesized by partial cationic substitution in (NH4)3ZrF7 cryolite. Due to small difference in ionic radii of K+ and NH4+, non-equivalent crystallographic positions 8c and 4b are occupied by both cations. Investigations of thermal, optical and structural properties in a wide range of temperature revealed two phase transitions Fm-3m ↔ P42/ncm ↔ P42/nmc of the first order. The results obtained are discussed in comparison with the data for the previously studied related cryolite (NH4)3ZrF7.
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20.

Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Gorev M. V., Mikhaleva E. A., Flerov I. N., Bogdanov E. V.
Заглавие : Conventional and inverse barocaloric effects in ferroelectric NH4HSO4
Место публикации : J. Alloys Compd. - 2019. - Vol. 806. - P.1047-1051. - ISSN 09258388 (ISSN), DOI 10.1016/j.jallcom.2019.07.273
Примечания : Cited References: 22
Аннотация: In this study, the conventional and inverse barocaloric effects (BCE) in ferroelectric NH4HSO4 are reported. Maximum extensive and intensive BCE near order–disorder phase transition can be achieved at low pressure p≤0.1 GPa. Large thermal expansion of the crystal lattice plays a very important role in the developing conventional BCE and conversation between BCE of different sign in the narrow temperature range.
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