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Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Mikhaleva E. A., Gorev M. V., Molokeev M. S., Kartashev A. V., Flerov I. N.
Заглавие : Anisotropy of piezocaloric effect at ferroelectric phase transitions in ammonium hydrogen sulphate
Место публикации : J. Alloys Compd. - 2020. - Vol. 839. - Ст.155085. - ISSN 09258388 (ISSN), DOI 10.1016/j.jallcom.2020.155085
Примечания : Cited References: 31. - The reported study was supported by the Russian Science Foundation (project no. 19-72-00023 ). 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: The role of anisotropy of the thermal expansion in formation of piezocaloric effect (PCE) near ferroelectric phase transitions in NH4HSO4 was studied. Strong difference in linear baric coefficients and as a result in intensive and extensive PCE associated with the different crystallographic axes was found. PCE giving the main contribution to the barocaloric effect were determined at both phase transitions. Rather strong effect of the lattice dilatation on the tuning of PCE was observed. Comparative analysis of PCE at the phase transitions in different materials showed that NH4HSO4 can be considered as a promising solid-state refrigerant. A hypothetical cooling cycle based on alternate using uniaxial pressure along two axes was considered.
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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 журнала
Шифр издания :
Автор(ы) : Gorev M. V., Kartashev A. V., Bogdanov E. V., Flerov I. N., Laptash N. M.
Заглавие : Calorimetric, dilatometric and DTA under pressure studies of the phase transitions in elpasolite (NH4)2KZrF7
Место публикации : J. Fluor. Chem. - 2020. - Vol. 235. - Ст.109523. - ISSN 00221139 (ISSN), DOI 10.1016/j.jfluchem.2020.109523
Примечания : Cited References: 45. - 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: Heat capacity, thermal expansion, and sensitivity to the hydrostatic pressure of (NH4)2KZrF7 elpasolite are studied in a wide temperature range. The changes in deformation and entropy during successive phase transitions are determined: Δ(ΔV/V) = 3·10−4; ΔS = 8 J/mol K The temperatures and entropies of phase transitions turned out to be slightly sensitive to pressure changes. An analysis of the entropy of phase transformations was performed in the framework of the model of the cubic phase structure Fm-3 m. In the low temperature phase, an anomalous behavior of thermodynamic properties, which is not characteristic of phase transitions, was observed, accompanied by a significant change in the crystal lattice entropy.
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Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Flerov I. N., Gorev M. V., Bogdanov E. V., Laptash N. M.
Заглавие : Chemical pressure as an effective tool for tuning the structural disordering and barocaloric efficiency of complex fluorides (NH4)3MF7 (M: Sn, Ti, Ge, Si)
Колич.характеристики :18 с
Место публикации : J. Phys. D: Appl. Phys. - 2024. - Vol. 57, Is. 17. - Ст.175301. - ISSN 00223727 (ISSN), DOI 10.1088/1361-6463/ad211b. - ISSN 13616463 (eISSN)
Примечания : Cited References: 39. - The study was supported by a Grant from the Russian Science Foundation No. 23-22-00115, https://rscf.ru/project/23-22-00115/
Аннотация: Double fluoride salts (NH4)3M4+F7 (M4+: Sn, Ti, Ge, Si) demonstrate a high efficiency of using chemical pressure as a tool for control and tuning structural ordering/disordering, sensitivity to hydrostatic pressure, successions of the phase transitions, etc and, as a result, for purposeful variation within a wide range of parameters of barocaloric effect (BCE). The conventional and inverse BCEs near the triple points were found on the T − p phase diagrams, combination of which can be used to construct original cooling cycle in narrow temperature and pressure ranges. Reconstructive transformation between two cubic phases, Pm3-m ↔ Pa3-, realized in (NH4)3SnF7 at atmospheric pressure and in (NH4)3TiF7 at p ˃ 0.4 GPa are characterized by rather low thermal hysteresis, δT0 = 1 K, and a great entropy change, ΔSBCE = 110–152 J (kg · K)−1, depending on the size of the central atom. At above 300–350 K, a contribution to BCE associated with the regular thermal expansion of the crystal lattice becomes comparable to entropy and temperature changes under pressure in the region of the phase transitions. An analysis of the absolute, relative and integral barocaloric characteristics of (NH4)3M4+F7 compounds showed their high competitiveness with respect to other barocaloric materials considered as promising solid-state refrigerants.
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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) : Mikhaleva E. A., Gorev M. V., Bondarev V. S., Bogdanov E. V., Flerov I. N.
Заглавие : Comparative analysis of elastocaloric and barocaloric effects in single-crystal and ceramic ferroelectric (NH4)2SO4
Место публикации : Scripta Mater. - 2021. - Vol. 191. - P.149-154. - ISSN 13596462 (ISSN), DOI 10.1016/j.scriptamat.2020.09.030
Примечания : Cited References: 47. - The reported study was supported by the Russian Science Foundation (project no. 19-72-00023 ). 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: We report the influence of anisotropy and texture on elasto(ElCE)- and baro(BCE)-caloric effects in single-crystal and ceramic (NH4)2SO4. Inverse extensive and intensive ElCE in ceramics, (ΔSElCE)cer = 87 J/kg·K; ΔTAD = - 11.6 K), as well as in a single crystal along the ferroelectric axis a, (ΔSElCE)a = 115 J/kg·K; (ΔTAD)a = - 16 K, significantly exceed BCE, ΔSBCE = 75 J/kg·K; ΔTAD = - 9.8 K, even at low pressure ~ 0.3 GPa. Caloric parameters of ammonium sulphate are comparable with those for promising solid-state refrigerants.
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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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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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Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Bondarev V. S., Mikhaleva E. A., Gorev M. V., Flerov I. N.
Заглавие : Direct and indirect studies of the electrocaloric effect in single crystalline ferrielectric (NH4)2SO4
Место публикации : J. Alloys Compd. - 2022. - Vol. 892. - Ст.162130. - ISSN 09258388 (ISSN), DOI 10.1016/j.jallcom.2021.162130
Примечания : Cited References: 38. - The reported study was supported by the Russian Science Foundation (project no. 19-72-00023)
Аннотация: The influence of an electric field on the phase transition parameters and the electrocaloric response in ferrielectric (NH4)2SO4 was studied using a universal multifunctional adiabatic calorimeter. The very low sensitivity of the phase transition temperature to the electric field, dT0/dE ≈ 5·10-3 K/(kV/cm), was shown to be the reason for the low maximum value of the intensive electrocaloric effect, ΔTAD, at E = 11 kV/cm: direct and indirect measurements gave the values of 0.01 K and 0.05 K, respectively. However, the extensive electrocaloric response revealed by an analysis of the entropy–temperature–electric field phase diagram was relatively large, with a value of ΔSECE ≈ − 19 J/kg K, due to the significant contribution of a jump in the excess entropy to the total value, δS0/ΔS0 ~ 0.37. An additional irreversible increase in temperature under the electric field was associated with the Joule effect and indicated a significant electrical conductivity of ammonium sulphate.
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10.

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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11.

Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Bogdanov E. V., Gorev M. V., Flerov I. N.
Заглавие : Effect of deuteration on the barocaloric properties of complex vanadates (NH4)3VOxF6−x (x: 1, 2)
Место публикации : Solid State Sci. - 2022. - Vol. 133. - Ст.107022. - ISSN 12932558 (ISSN), DOI 10.1016/j.solidstatesciences.2022.107022
Примечания : Cited References: 28
Аннотация: We report on the analysis of intensive and extensive barocaloric properties and their sensitivity to deuteration of complex oxyfluorides (NH4)3VOxF6−x (x: 1, 2) undergoing a similar sequence of structural phase transitions. Due to the high sensitivity to hydrostatic pressure and the strong disordering of six-coordinated anionic fluoro-oxygen species, (NH4)3VO2F4 and (ND4)3VO2F4 crystals demonstrate the highest barocaloric efficiency at low pressure, p = 0.1 GPa, during the phase transition from the initial cubic phase: barocaloric coefficients reach large values |ΔSBCE|/p ≈ 400 J/(kg K GPa) and ΔTAD/p ≈ 80 K/GPa. Anionic, [VOF5] → [VO2F4], and cationic, [ND4] → [NH4] substitutions are accompanied by a decrease in the disorder of structural units in the cubic phase, which leads to a decrease in changes in entropy and temperature under pressure. The contribution of thermal expansion of the crystal lattice to the total intensive and extensive barocaloric effects is large and amounts to about 30–40%.
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12.

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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13.

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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14.

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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15.

Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Mikhaleva E. A., Flerov I. N., Gorev M. V., Bondarev I. A., Bogdanov E. V.
Заглавие : Features of the behavior of the barocaloric effect near ferroelectric phase transition close to the tricritical point
Место публикации : Crystals. - 2020. - Vol. 10, Is. 1. - Ст.51. - ISSN 2073-4352, DOI 10.3390/cryst10010051
Примечания : Cited References: 28. - The reported study was supported by the Russian Science Foundation (project no. 19-72-00023)
Аннотация: A detailed study of the effect of temperature and pressure on heat capacity, entropy and hysteresis phenomena near the ferroelectric phase transition in ammonium sulfate (AS) was performed. An analysis of experimental results within the framework of the phenomenological theory showed that taking into account the temperature-dependent part of the anomalous entropy leads to a significant increase in the barocaloric effect (BCE). The maximum values of extensive and intensive BCE near the tricritical point are outstanding: ΔSmaxBCE≈85 J/kgK, ΔTmaxAD≈12 K and can be achieved at low pressure ∼0.5 GPa.
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16.

Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Mikhaleva E. A., Gorev M. V., Bondarev V. S., Molokeev M. S., Zaitsev A. I., Nemtsev I. V., Fokin A. V., Flerov I. N.
Заглавие : Heat capacity and thermal expansion of nanosized ferroelectric (NH4)2SO4 embedded in borosilicate glasses
Место публикации : J. Non-Cryst. Solids. - 2022. - Vol. 597. - Ст.121935. - ISSN 00223093 (ISSN), DOI 10.1016/j.jnoncrysol.2022.121935
Примечания : Cited References: 29. - The authors are grateful to Dr. Ewa Rysiakiewicz-Pasek (Wroclaw University of Science and Technology, Poland) for the preparation and characterization of borosilicate glasses. 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: The thermal properties of nanocomposites obtained by incorporating a ferroelectric (NH4)2SO4 (AS) into porous glasses (PG) was studied for the first time. X-ray diffraction studies showed a strong increase in the ratio of the size of nanocrystallites grown in glass matrices to pore size, dcryst/ dpore = 0.47→1.50→5.00, with a decrease in dpore = 320→46→7 nm. Calorimetric and dilatometric measurements showed a change from a first-order phase transition in AS single crystal to a second-order transformation in AS nanocrystallites. A restricted geometry also led to a significant decrease in the anomalous entropy in AS+PG samples compared to AS (J/mol∙K): 17.7 (AS)→12.4 (AS+PG320)→10.4 (AS+PG46)→8.1 (AS+PG7). A discussion of the nontrivial behavior of the phase transition temperature in embedded AS was carried out using the degree of PG filling, the ratio dcryst/dpore, texture, and the volumetric and linear baric coefficients for the bulk AS.
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17.

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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18.

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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19.

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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20.

Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Gorev M. V., Molokeev M. S., Kartashev A. V., Pogoreltsev E. I., Mel'nikova S. V., Laptash N. M., Flerov I. N.
Заглавие : Investigation of thermal properties and structure of complex fluoride K3ZrF7
Место публикации : J. Fluor. Chem. - 2021. - Vol. 241. - Ст.109677. - ISSN 00221139 (ISSN), DOI 10.1016/j.jfluchem.2020.109677
Примечания : Cited References: 44. - 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 K3ZrF7 revealed the existence of the phase transition Fm-3m ↔ R-3m at T0 = 320 K. The structural model assumes a disorder of a pentagonal bipyramid ZrF7 with the following ratio of equivalent orientation positions in the initial and distorted phases: 12 to 6. A good agreement was found between the experimental and model-calculated changes in strain and entropy during the phase transition. A comparative analysis of entropy and structural parameters of related fluorides K3ZrF7 - (NH4)2KZrF7 - (NH4)3ZrF7 was performed. The anomalous behavior of thermodynamic properties in the range 140−230 K is not typical for phase transitions and is accompanied by a significant change in the entropy of the crystal lattice.
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