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Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : ZEIN N. E., ZINENKO V. I., FEDOROV A. S.
Заглавие : ABINITIO CALCULATIONS OF PHONON FREQUENCIES AND DIELECTRIC-CONSTANTS IN A(4)B(6) COMPOUNDS
Место публикации : Phys. Lett. A: ELSEVIER SCIENCE BV, 1992. - Vol. 164, Is. 1. - P115-119. - ISSN 0375-9601, DOI 10.1016/0375-9601(92)90916-A
Примечания : Cited References: 20
Предметные рубрики: IV-VI COMPOUNDS
CRYSTAL-STRUCTURE
Аннотация: The transverse and longitudinal optical frequencies at q = 0, the dielectric constant and the effective charges are calculated for the A4B6 type family of the semiconducting compounds GeTe, SnTe and PdTe. The calculations are performed in the framework of the density functional method with the use of the norm-conserving "first-principles" pseudopotentials. The estimated ferroelectric phase transition temperatures and a number of other calculated quantities turned out to be in good agreement with the experimental data. The variations of the electronic structure in the row PbTe-GeTe, which promote the ferroelectric phase transition for GeTe, are discussed.
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Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Flerov I. N., Aleksandrov K. S., Tressaud A., Grannec J., Couzi M.
Заглавие : Phase transitions in elpasolites (ordered perovskites)
Место публикации : Materials Science and Engineering R: Reports. - 1998. - Vol. 24, Is. 3. - P.81-151. - ISSN 0927-796X
Примечания : Cited References: 174
Предметные рубрики: ELASTIC NEUTRON-DIFFRACTION
MII = CO
RAMAN-SCATTERING
THERMODYNAMIC PROPERTIES
CRYSTAL-STRUCTURE
SINGLE-CRYSTALS
RB2KMIIIF6 ELPASOLITES
CUBIC PEROVSKITES
TEMPERATURE FORM
HIGH-RESOLUTION
Ключевые слова (''Своб.индексиров.''): crystal atomic structure--crystal growth--crystal lattices--crystallization--crystallography--ferroelectricity--hydrostatic pressure--order disorder transitions--single crystals--thermodynamics--elpasolites--landau theory--perovskite
Аннотация: Many compounds with general chemical formula A2BB?X6 and with tolerance factor value t < 1 crystallize in the elpasolite (ordered perovskite) structure. Different preparative methods have been considered. For example, the Bridgman technique is the most suitable method of growing single crystals of halogenated elpasolites with monoatomic cations. Group-theory and symmetry analyses have allowed us to build a scheme of possible structural distortions connected with octahedral rotations and displacements of ions. Experimental observations have proven that ferroelastic phase transitions occurring most frequently in elpasolites are due to small octahedra tilts. Quantitative analysis allows the possibility of describing these transitions in the framework of the thermodynamic Landau theory. Hydrostatic pressure and the substitution of atoms in different crystallographic sites allow to change significantly the succession and the temperature of phase transitions. The hypothesis of bond stresses is able to predict the possible occurrence of a phase transition for a particular elpasolite and/or the role of the octahedra rotations in the transformation. The mechanism of phase transitions in elpasolites and related compounds has also been considered. One can assume that a displacive mechanism associated with a strong anharmonicity plays a large role in phase transitions occurring in compounds with monoatomic cations. On the other hand, for instance, in cryolites with ammonium cations, the transitions originate from an order-disorder phenomenon. В© 1998 Elsevier Science S.A. All rights reserved.
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Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Flerov I. N., Gorev M. V., Sciau P.
Заглавие : Heat capacity and p-T phase diagrams of the ordered perovskites Pb2MgWO6 and Pb2CoWO6
Место публикации : J. Phys.: Condens. Matter: IOP PUBLISHING LTD, 2000. - Vol. 12, Is. 5. - P.559-567. - ISSN 0953-8984, DOI 10.1088/0953-8984/12/5/304
Примечания : Cited References: 25
Предметные рубрики: CRYSTAL-STRUCTURE
X-RAY
TRANSITIONS
PRESSURE
Аннотация: The heat capacities of Pb2MgWO6 and Pb2CoWO6 and the effect of hydrostatic pressure on the phase transitions have been studied on powdered samples by means of an adiabatic calorimeter and DTA performed under pressure, respectively. Thermodynamic parameters, such as change of total excess entropy, latent hear and hysteresis of the phase transition temperature were determined. Entropies and p-T phase diagrams are discussed in connection with structural data.
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Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Lundin U., Sandalov I., Eriksson O., Johansson B.
Заглавие : Modification of the standard model for the lanthanides
Место публикации : Solid State Commun.: PERGAMON-ELSEVIER SCIENCE LTD, 2000. - Vol. 115, Is. 1. - P7-12. - ISSN 0038-1098, DOI 10.1016/S0038-1098(00)00126-5
Примечания : Cited References: 33
Предметные рубрики: ELECTRONIC-STRUCTURE CALCULATIONS
DENSITY-FUNCTIONAL THEORY
PARTICLE BAND-STRUCTURE
AB-INITIO CALCULATIONS
FERROMAGNETIC NICKEL
COHESIVE PROPERTIES
CRYSTAL-STRUCTURE
MOTT INSULATORS
FERMION SYSTEMS
PR METAL
Ключевые слова (''Своб.индексиров.''): metals--electronic band structure--band structure--elastic moduli--kohn-sham scheme--rare earth elements
Аннотация: We show that incorporation of strong electron correlations into the Kohn-Sham scheme of band structure calculations leads to a modification of the standard model of the lanthanides and that this procedure removes the existing discrepancy between theory and experiment concerning the ground state properties. Within the picture suggested, part of the upper Hubbard f-band is occupied due to conduction band-f-mixing interaction (that is renormalized due to correlations) and this contributes to the cohesive energy of the crystal. The lower Hubbard band has zero width and describes fermionic excitations in the shell of localized f-s. Fully self-consistent calculations (with respect to both charge density and many-electron population numbers of the f-shell) of the equilibrium volume V-0 and the bulk modulus of selected lanthanides have been performed and a good agreement with experiment is obtained. (C) 2000 Elsevier Science Ltd. All rights reserved.
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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) : Gorev M. V., Flerov I. N., Sciau P.
Заглавие : Heat capacity and the p-T phase diagram of Pb2MgTeO6 elpasolite
Место публикации : Phys. Solid State: AMER INST PHYSICS, 2001. - Vol. 43, Is. 2. - P345-349. - ISSN 1063-7834, DOI 10.1134/1.1349486
Примечания : Cited References: 17
Предметные рубрики: ORDERED PEROVSKITE PB2MGTEO6
CRYSTAL-STRUCTURE
PB2COWO6
PB2MGWO6
Аннотация: The heat capacity of Pb2MgTeO6 is measured in the temperature range 80-300 K. It is found that the heat capacity exhibits an anomaly associated with the phase transition at T-0 = 186.9 K. The thermodynamic parameters of the structural transformation are determined. The effect of hydrostatic pressure up to 0.5 GPa on the phase transition temperature is examined. (C) 2001 MAIK "Nauka/Interperiodica".
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Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Gorev M. V., Flerov I. N., Bondarev V. S., Sciau P.
Заглавие : Studies of the thermodynamic properties of the ordered perovskites Pb2CdWO6 and Pb2YbTaO6 within a broad temperature range
Место публикации : Phys. Solid State: AMER INST PHYSICS, 2002. - Vol. 44, Is. 2. - P353-357. - ISSN 1063-7834, DOI 10.1134/1.1451027
Примечания : Cited References: 18
Предметные рубрики: CRYSTAL-STRUCTURE
PB2COWO6
PB2MGWO6
PHASE
HEAT
Аннотация: This paper reports on measurements of the specific heat of Pb2CdWO6 made at temperatures ranging from 80 to 750 K and of Pb2YbTaO6 within the 350- to 700-K temperature range. First-order phase transitions from the cubic phase at 677.3 and 581 K, respectively, were observed, and their thermodynamic characteristics were determined. The entropy change on the phase transitions is close to Rln4 for both compounds. The results obtained are discussed in terms of the model of position disordering of the lead ions. It was established that below 350 K, Pb2CdWO6 can exist in two states, stable and metastable, depending on the sample thermal prehistory. (C) 2002 MAIK "Nauka/Interperiodica".
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Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Balaev A. D., Bayukov O. A., Vasil'ev A. D., Velikanov D. A., Ivanova N. B., Kazak N. V., Ovchinnikov S. G., Abd-Elmeguid M. M., Rudenko V. V.
Заглавие : Magnetic and electrical properties of Fe1.91V0.09BO4 warwickite
Разночтения заглавия :авие SCOPUS: Magnetic and electrical properties of Fe1.91V 0.09BO4 warwickite
Место публикации : J. Exp. Theor. Phys.: AMER INST PHYSICS, 2003. - Vol. 97, Is. 5. - P989-995. - ISSN 1063-7761, DOI 10.1134/1.1633954
Примечания : Cited References: 22. - This study was supported in part by the Russian Foundation for Basic Research (project no. 03-02-16286) and by the Federal Program “Integration” (project no. B0017)
Предметные рубрики: ELECTRONIC-STRUCTURE
CRYSTAL-STRUCTURE
FE2OBO3
CHAINS
FE2BO4
FEBO3
Ключевые слова (''Своб.индексиров.''): electric conductivity--magnetic variables measurement--magnetization--single crystals--hopping conductivity--warwickite--iron compounds
Аннотация: We have performed a complex investigation of the structure and the magnetic and electrical properties of a warwickite single crystal with the composition Fe1.91V0.09BO4 . The results of Mossbauer measurements at T = 300 K indicate that there exist "localized" (Fe2+, Fe3+) and "delocalized" (Fe2.5+) states distributed over two crystallographically nonequivalent positions. The results of magnetic measurements show that warwickite is a P-type ferrimagnet below T = 130 K. The material exhibits hopping conductivity involving strongly interacting electrons. The experimental data are analyzed in comparison to the properties of the initial (unsubstituted) Fe2BO4 warwickite. The entire body of data on the electric conductivity and magnetization are interpreted on a qualitative basis. (C) 2003 MAIK "Nauka / Interperiodica".
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Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Volkov N. V., Sablina K. A., Bayukov O. A., Eremin E. V., Petrakovskii G. A., Velikanov D. A., Balaev A. D., Bovina A. F., Boni P., Clementyev E.
Заглавие : Magnetic properties of the mixed-valence manganese oxide Pb(3)Mn(7)O(15)
Разночтения заглавия :авие SCOPUS: Magnetic properties of the mixed-valence manganese oxide Pb 3Mn7O15
Место публикации : J. Phys.: Condens. Matter: IOP PUBLISHING LTD, 2008. - Vol. 20, Is. 5. - Ст.55217. - ISSN 0953-8984, DOI 10.1088/0953-8984/20/5/055217
Примечания : Cited References: 16
Предметные рубрики: CRYSTAL-STRUCTURE
PHASE-SEPARATION
Ключевые слова (''Своб.индексиров.''): crystal structure--magnetization--manganese compounds--phase interfaces--x ray diffraction--manganese oxide--space groups--temperature range--single crystals
Аннотация: A Pb(3)Mn(7)O(15) single crystal has been grown by the flux method and studied using x-ray diffraction and magnetization measurements. The crystal is hexagonal (P6(3)/mcm space group, Z = 4) and exhibits a pronounced layered nature. Along the [001] direction (c axis), the structure consists of layers of edge-sharing MnO(6) octahedra. Pairs of Mn atoms occupy the octahedral sites located between layers forming 'bridges' along the c axis, which link neighboring Mn layers. The magnetic properties of the crystal have been investigated using ac and dc magnetization measurements in the temperature range 2-900 K at magnetic fields up to 90 kOe. The experimental data obtained suggest that in the temperature region under study several different magnetic phases can be distinguished. Down to similar to 250 K, the crystal is in the paramagnetic state. Below this temperature, short-range antiferromagnetic ordering apparently starts forming within Mn layers, although a transition to long-range magnetic order occurs at 70 K. The magnetization data obtained leads us to conclude that this state is canted antiferromagnetic with moments lying in the basal plane of the crystal. In addition, below 20 K the crystal undergoes one more magnetic transition that corresponds to spin reorientation.
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10.

Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Zvyagina G. A., Zhekov K. R., Bezmaternykh L. N., Gudim I. A., Bilych I. V., Zvyagin A. A.
Заглавие : Magnetoelastic effects in terbium ferroborate
Место публикации : Low Temp. Phys. - 2008. - Vol. 34, Is. 11. - P.901-908. - ISSN 1063-777X, DOI 10.1063/1.3009584; \b Физика низких температур
Примечания : Cited References: 17
Предметные рубрики: CRYSTAL-STRUCTURE
ND
Ключевые слова (''Своб.индексиров.''): acoustic wave velocity--antiferromagnetic materials--elastic moduli--exchange interactions (electron)--iron compounds--magnetoelastic effects--solid-state phase transformations--terbium compounds
Аннотация: The behavior of the elastic moduli and sound absorption in a terbium orthoborate single crystal at low temperatures is studied. The components of the tensor of the elastic moduli of this system are determined. A structural phase transition and a transition of the magnetic subsystem into an antiferromagnetically ordered state appear in the temperature dependences of the sound velocities and absorption. The magnetic field dependences of the velocities of transverse sound exhibit singularities in the form of jumps at a magnetic field equal to the field of the spin-flop transition of the antiferromagnetic subsystem. Theoretical analysis shows that the observed behavior of the acoustic characteristics are associated not with the rare-earth subsystem of ferroborate but rather with the renormalization of the exchange interaction between iron ions as a result of the magnetoelastic coupling.
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11.

Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Ivanova N. B., Ovchinnikov S. G., Korshunov M. M., Eremin I. M., Kazak N. V.
Заглавие : Specific features of spin, charge, and orbital ordering in cobaltites
Коллективы : RFBR [09-02-00171-a, 07-02-00226, 09-02-00127]; Federal Agency of Science and Innovation [MK-4278.2008.2]; Presidium of the Russian Academy of Sciences [5, 7]; Leading Science Schools of the Ministry of Education and Science of the Russian Federation [2.1.1/3199]
Место публикации : Phys. Usp.: Turpion Ltd, 2009. - Vol. 52, Is. 8. - P.789-810. - ISSN 1063-7869, DOI 10.3367/UFNe.0179.200908b.0837
Примечания : Cited References: 278. - This work was financially supported by the RFBR (projects 09-02-00171-a, 07-02-00226, and 09-02-00127), the Federal Agency of Science and Innovation (grant MK-4278.2008.2), and the Presidium of the Russian Academy of Sciences Program No. 5, Quantum Physics of Condensed Media (project No. 7). I.M.E.'s work was supported by the program for Leading Science Schools of the Ministry of Education and Science of the Russian Federation (grant 2.1.1/3199).
Предметные рубрики: PEROVSKITE-TYPE OXIDES
METAL-INSULATOR-TRANSITION
HIGH-TEMPERATURE SUPERCONDUCTIVITY
ONE-DIMENSIONAL CA3CO2O6
ELECTRONIC-STRUCTURE
MAGNETIC-PROPERTIES
TRANSPORT-PROPERTIES
STATE TRANSITION
FUEL-CELLS
CRYSTAL-STRUCTURE
Ключевые слова (''Своб.индексиров.''): cobalt oxides--lanthanides--orbital degrees of freedom--orbital ordering--quasi-one-dimensional--spin state--superconducting compounds--theoretical result--calcium--cobalt--lanthanum--oxide minerals--perovskite--spin dynamics--superconductivity--cobalt compounds
Аннотация: Complex cobalt oxides known as cobaltites are reviewed, including LnCoO(3)-based perovskite-structured rare-earth cobaltites (where Ln is lanthanum or a lanthanide), quasi-two-dimensional and quasi-one-dimensional cobaltites of the types LnCo(2)O(5+delta), La2CoO4, and Ca3Co2O8, and NaxCoO2 center dot yH(2)O superconducting compounds. Key experimental and theoretical results are presented, with emphasis on the interplay between charge, spin, and orbital degrees of freedom. Two problems of specific relevance to cobaltites - the spin state instability of Co3+ ions in LnCoO(3), and the nature of superconductivity in NaxCoO2 center dot yH(2)O - are also given significant attention.
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12.

Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Mel'nikova S. V., Isaenko L. I., Gorev M. V., Vasil'ev A. D., Lobanov S. I.
Заглавие : Investigation of the structure, physical properties, and phase transition in SrAlF5
Коллективы :
Место публикации : Phys. Solid State: MAIK NAUKA/INTERPERIODICA/SPRINGER, 2010. - Vol. 52, Is. 3. - P509-514. - ISSN 1063-7834, DOI 10.1134/S1063783410030108
Примечания : Cited References: 16. - This study was supported by the Russian Foundation for Basic Research (project no. 07-02-00442) and the Siberian Branch of the Russian Academy of Sciences within the framework of the Interdisciplinary Integration Project No. 34.
Предметные рубрики: CRYSTAL-STRUCTURE
BEHAVIOR
GROWTH
SRAIF5
Аннотация: Crystals of SrAlF5 have been grown by the Bridgman method from the melt and by sintering of the components. Optical polarization studies and measurements of the thermal expansion and birefringence coefficients have been carried out over a wide temperature range. The electromechanical coefficient d (33) has been measured, and the optical second harmonic, dielectric hysteresis loop, and optical quality of the crystal have been assessed. X-ray diffraction investigations have been performed to identify the revealed compounds. It has been demonstrated that the SrAlF5 crystals obtained under the growth conditions chosen have I4(1)/a symmetry and do not undergo structural phase transitions in the temperature range 100-800 K. Crystalline inclusions of the AlOF oxyfluoride have been revealed in crystals grown with an AlF3 excess. The birefringence of the AlOF crystal is an order of magnitude higher than that of SrAlF5, does not depend on temperature, and has no anomalies up to 800 K.
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13.

Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Fokina V. D., Bogdanov E. V., Gorev M. V., Molokeev M. S., Pogorel'tsev E. I., Flerov I. N., Laptash N. M.
Заглавие : Phase transitions in the (NH4)(2)NbOF5 oxyfluoride
Коллективы :
Разночтения заглавия :авие SCOPUS: Phase transitions in the (NH4)2NbOF5 oxyfluoride
Место публикации : Phys. Solid State: MAIK NAUKA/INTERPERIODICA/SPRINGER, 2010. - Vol. 52, Is. 4. - P781-788. - ISSN 1063-7834, DOI 10.1134/S1063783410040189
Примечания : Cited References: 13. - We would like to thank A. A. Udovenko (Institute of Chemistry, Far Eastern Branch, Russian Academy of Sciences, Vladivostok, Russia) for kindly supplied detailed data on the atomic coordinates in the structure of the (NHINF4/INF)INF2/INFNbOFINF5/INF oxyfluoride.This study was supported by the Russian Foundation for Basic Research (project no. 09-02-00062) and the Council on Grants from the President of the Russian Federation for Support of Leading Scientific Schools of the Russian Federation (grant no. NSh-1011.2008.2).
Предметные рубрики: CRYSTAL-STRUCTURE
(NH4)(2)WO2F4
MECHANISM
DISORDER
Аннотация: The thermal and dielectric properties of the (NH4)(2)NbOF5 oxyfluoride have been investigated. It has been established that the structural phase transitions Cmc2(1) - C2 - Ia observed at the temperatures T (1) = 258.0 K and T (2) = 218.9 K exhibit a nonferroelectric nature. The hydrostatic pressure, which stabilizes the initial phase and destabilizes the low-temperature phase, hardly affects the temperature range of stability of the intermediate phase. The model of sequential ordering of the structural elements due to phase transitions has been analyzed using experimental data on the entropies of the phase transitions.
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14.

Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Popova E. A., Vasiliev A. N., Temerov V. L., Bezmaternykh L. N., Tristan N., Klingeler R., Buchner B.
Заглавие : Magnetic and specific heat properties of YFe3(BO3)(4) and ErFe3(BO3)(4)
Коллективы :
Разночтения заглавия :авие SCOPUS: Magnetic and specific heat properties of YFe3(BO3) 4 and ErFe3(BO3)4
Место публикации : J. Phys.: Condens. Matter: IOP PUBLISHING LTD, 2010. - Vol. 22, Is. 11. - Ст.116006. - ISSN 0953-8984, DOI 10.1088/0953-8984/22/11/116006
Примечания : Cited References: 26. - This work was supported by DFG grants 436 RUS and HE 3439/6 (FOR 520). The authors are indebted to M N Popova and B Z Malkin for valuable discussions.
Предметные рубрики: LINEAR-CHAIN ANTIFERROMAGNETISM
CRYSTAL-STRUCTURE
GDFE3(BO3)(4)
MULTIFERROICS
BA2COS3
ORDER
Ключевые слова (''Своб.индексиров.''): antiferromagnetic orders--basal planes--experimental data--magnetically ordered state--antiferromagnetism--calorimetry--erbium--magnetic moments--single crystals--specific heat--magnetic domains
Аннотация: The present paper reports on the specific heat and magnetization of the YFe3(BO3)(4) and ErFe3(BO3)(4) single crystals. In both compounds, antiferromagnetic order of the iron spins evolves at T-N = 38 K. The experimental data suggest that the magnetic moments are in the basal plane of the trigonal crystal for both compounds. In the magnetically ordered state the crystal is subdivided into three types of domains, the magnetic moments of the Fe3+ ions being aligned along the a axis within each domain. For ErFe3(BO3)(4), two non-equivalent magnetic positions of the Er3+ ions in each domain are observed.
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15.

Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Vasiliev, Alexander D., Cherepakhin, Alexander V., Zaitsev, Alexander I.
Заглавие : The trigonal polymorph of strontium tetraborate, beta-SrB4O7
Место публикации : Acta Crystallogr. Sect. E.-Struct Rep. Online. - MALDEN: WILEY-BLACKWELL, 2010. - Vol. 66, Part 6. - С. I48-U132. - JUN. - ISSN 1600-5368, DOI 10.1107/S1600536810019069
Примечания : Cited Reference Count: 22. - Гранты: We thank the State Program for Support of Leading Scientific Schools (grant LS-4645.2010.2.)Финансирующая организация: Leading Scientific Schools [LS-4645.2010.2]
Предметные рубрики: CRYSTAL-STRUCTURE
SRB4O7
LUMINESCENCE
MODEL
Ключевые слова (''Своб.индексиров.''): tetra
Аннотация: The asymmetric unit of the title compound, beta-SrB4O7, contains five Sr atoms (three located on a threefold rotation axis), twelve B and 21 O atoms. The structure is made up from BO3 triangles and BO4 tetrahedra in a 1:1 ratio. Pairs of BO3 triangles are linked to BO4 tetrahedra via common corners, forming chains. These chains are further linked to adjacent chains through corner-sharing, leading to a three-dimensional framework with channels running parallel to [001]. The Sr2+ ions reside in the channels and exhibit strongly distorted polyhedra The density of the beta-polymorph is considerably lower than that of beta-SrB4O7, which is constructed solely from BO4 tetrahedra.
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16.

Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Gorev M., Bogdanov E. V., Flerov I. N., Laptash N. M.
Заглавие : Thermal expansion, phase diagrams and barocaloric effects in (NH4)(2)NbOF5
Коллективы :
Разночтения заглавия :авие SCOPUS: Thermal expansion, phase diagrams and barocaloric effects in (NH 4)2NbOF5
Место публикации : J. Phys.: Condens. Matter: IOP PUBLISHING LTD, 2010. - Vol. 22, Is. 18. - Ст.185901. - ISSN 0953-8984, DOI 10.1088/0953-8984/22/18/185901
Примечания : Cited References: 17. - This work was supported in part by the Krasnoyarsk Regional Foundation for Support of Scientific and Scientific-Technological Investigations and RFBR in the framework of project 'Siberia' (Grant No. 09-02-98001), and the Council on Grants from the President of the Russian Federation for Support of Leading Scientific Schools (project No. Nsh-1011.2008.2).
Предметные рубрики: CRYSTAL-STRUCTURE
SOLID-STATE
OXYFLUORIDE
TRANSITION
ANION
Ключевые слова (''Своб.индексиров.''): antiferromagnets--ferromagnets--heat capacities--high stress--intermediate phase--pippard relations--structural phase transition--transition temperature--uniaxial pressures--financial data processing--phase diagrams--phase transitions--thermal stress--tools--thermal expansion
Аннотация: The thermal expansion along the a, b and c axes of a (NH4)(2)NbOF5 crystal was measured from 120 to 300 K. Anomalies of alpha(T) associated with previously reported phase transitions Cmc2(1) - C-2 - I a were observed along all directions at T-1 = 259.3 K and T-2 = 220.5 K. The analysis of thermal expansion and heat capacity in the frame of the Pippard relations has permitted us to determine the uniaxial pressure derivatives of the transition temperatures dT/d sigma(i). The T-sigma(i) phase diagrams have shown a tendency for the intermediate phase to disappear at high stress along the b and c axes. Intensive and extensive barocaloric effects near the structural phase transitions were found to be comparable with the caloric parameters of some ferroelectrics, ferromagnets and antiferromagnets.
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17.

Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Ovchinnikov S. G., Antipina L. Yu., Tomilin F. N., Kuzubov A. A.
Заглавие : Effect of electron correlations on the structure of photoprotein substrates
Коллективы :
Место публикации : JETP Letters. - 2010. - Vol. 91, Is. 9. - P.490-493. - ISSN 0021-3640, DOI 10.1134/S0021364010090122
Примечания : Cited References: 14. - This work was supported by the Russian Foundation for Basic Research (project no. 07-04-00930-a), by the Presidium of the Russian Academy of Sciences (program "Molecular and Cellular Biology"), and by the Siberian Branch, Russian Academy of Sciences (project no. 2).
Предметные рубрики: ANGSTROM RESOLUTION
CRYSTAL-STRUCTURE
AEQUORIN
ENERGY
OBELIN
GAS
Аннотация: The electronic structure and total energy of various isomeric forms of coelenterazine and coelenteramide have been calculated by quantum chemistry methods both in the single-electron approximation and taking into account correlation effects. It has been shown that the inclusion of electron correlations makes it possible to obtain the structure of the coelenteramide close to the experimentally determined structure, as well as to choose the structure of the coelenterazine CLZ(1H) as the most probable isomeric form.
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18.

Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Atuchin V. V., Chimitova O. D., Gavrilova T. A., Molokeev M. S., Kim S. J., Surovtsev N. V., Bazarov B. G., Bazarova Zh.G.
Заглавие : Synthesis, structural and vibrational properties of microcrystalline RbNd(MoO4)(2)
Коллективы : International Conference on Crystal Growth, International Conference on Vapor Growth and Epitaxy
Место публикации : J. Cryst. Growth: Elsevier Science BV, 2011. - Vol. 318, Is. 1. - P.683-686. - ISSN 0022-0248, DOI 10.1016/j.jcrysgro.2010.09.076
Примечания : Cited References: 26
Предметные рубрики: MOLYBDENUM TRIOXIDE
DOUBLE MOLYBDATES
CRYSTAL-STRUCTURE
GROWTH
LASER
MOO3
Ключевые слова (''Своб.индексиров.''): crystal structure--solid state synthesis--molybdate
Аннотация: Rubidium neodymium dimolybdate, RbNd(MoO4)(2), microcrystals have been fabricated by solid state synthesis at T=550-600 degrees C by t=324 ks. Crystal structure of RbNd(MoO4)(2) has been refined by Rietveld method in space group Pbcn with cell parameters a = 5.1772(1) angstrom, b = 18.7293(4) angstrom, and c = 8.2774(1) angstrom (R-B=5.05%). The crystal structure of RbNd(MoO4)(2) consists of layers of MoO4 tetrahedrons cornersharing with NdO8 square antiprisms. These layers are perpendicular to b-axis of the unit cell. About 20 narrow Raman lines have been observed in Raman spectrum recorded for RbNd(MoO4)(2) powder sample. (C) 2010 Elsevier B.V. All rights reserved.
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19.

Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Antonova A. B., Chudin O. S., Vasiliev A. D., Rubaylo A. I., Verpekin V. V., Sokolenko W. A., Pavlenko N. I., Semeikin O. V.
Заглавие : Chemistry of vinylidene complexes. XX. Intramolecular carbonylation of vinylidene on the MnFe center: Spectroscopic and structural study. X-ray structure of the new trimethylenemethane type MnFe complex
Место публикации : J. Organomet. Chem.: Elsevier, 2011. - Vol. 696, Is. 4. - P.963-970. - ISSN 0022-328X, DOI 10.1016/j.jorganchem.2010.10.035
Примечания : Cited References: 52. - This work was partially supported by the Presidium of the Russian Academy of Sciences (Program for Basic Research, Project No. 7.18) and Russian Foundation for Basic Research (Grant No. 09-03-90745-mob_st). Authors are grateful to Prof. N.A. Ustynyuk for useful discussions, Dr. E.A. Shor and Dr. A.M. Shor for giving the data of quantum chemical study.
Предметные рубрики: MOLECULAR-STRUCTURE
ORGANOMETALLIC CHEMISTRY
TRICARBONYL COMPLEXES
UNSATURATED CARBENES
METAL VINYLIDENES
TRANSITION-METALS
ORGANIC-SYNTHESIS
CRYSTAL-STRUCTURE
IRON TRICARBONYL
MANGANESE
Ключевые слова (''Своб.индексиров.''): manganese--iron--carbonyl complexes--heteronuclear vinylidene complexes--intramolecular vinylidene carbonylation--trimethylenemethane complexes
Аннотация: Reactions of Fe-2(CO)(9) with Cp(CO)(2)Mn=C=CHPh (1) and Cp(CO)(PPh3)Mn=C=CHPh (3) gave the heterometallic trimethylenemethane complexes eta(4)-{C[Mn(CO)(2)Cp](CO)CHPh}Fe(CO)(3) (2) and eta(4)-{C[Mn(CO)(PPh3)Cp](CO)CHPh}Fe(CO)(3) (4), respectively. The formation of the benzylideneketene [PhHC=C=C=O] fragment included in complexes 2 and 4 occurs via intramolecular coupling of the carbonyl and vinylidene ligands. The structures of 3 and 4 were determined by single crystal XRD methods. The influence of the nature of the L ligands at the Mn atom on the structural and spectroscopic characteristics of eta(4)-{C[Mn(CO)(L)Cp](CO)CHPh}Fe(CO)(3) (L = CO (2), PPh3 (4)) is considered. According to the VT H-1 and C-13 NMR spectra, complex 2 reversibly transforms in solution into mu-eta(1):eta(1)-vinylidene isomer Cp(CO)(2)MnFe(mu-C=CHPh)(CO)(4) (2a), whereas complex 4 containing the PPh3 ligand is not able to a similar transformation. (C) 2010 Elsevier B.V. All rights reserved.
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20.

Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Bartolome J., Arauzo A., Kazak N. V., Ivanova N. B., Ovchinnikov S. G., Knyazev Yu. V., Lyubutin I. S.
Заглавие : Uniaxial magnetic anisotropy in Co2.25Fe0.75O2BO3 compared to Co3O2BO3 and Fe3O2BO ludwigites
Разночтения заглавия :авие SCOPUS: Uniaxial magnetic anisotropy in Co2.25Fe0.75O 2BO3 compared to Co3O2BO3 and Fe3O2BO ludwigites
Место публикации : Phys. Rev. B: AMER PHYSICAL SOC, 2011. - Vol. 83, Is. 14. - Ст.144426. - ISSN 1098-0121, DOI 10.1103/PhysRevB.83.144426
Примечания : Cited References: 25. - The authors acknowledge V. V. Rudenko for the oxyborate samples they made and O. A. Bayukov for fruitful discussion. The financial support of Spanish MINCYT, Grant No. MAT08/1077, and the Aragonese E-34 project are acknowledged. Fruitful discussions with F. Bartolome and P. Bordet are acknowledged. The latter is thanked for providing the FeINF3/INFOINF2/INFBOINF3/INF single crystal. Also this study was supported by the Russian Foundation for Basic Research (Project No. 09-02-00171-a), the Federal Agency for Science and Innovation (Rosnauka) (Project No. MK-5632.2010.2), and the Physical Division of the Russian Academy of Science (Program "Strongly Correlated Electrons," Project No. 2.3.1).
Предметные рубрики: CRYSTAL-STRUCTURE
MOSSBAUER
CO3BO5
Аннотация: Magnetic and Mossbauer spectroscopy (MS) measurements have been performed on a single crystal of Co2.25Fe0.75O2BO3 with ludwigite structure. Two magnetic transitions (T-N = 115 K and T-C = 70 K) were traced from the ac susceptibility temperature dependence. The MS spectra as a function of temperature clearly show the onset of magnetic ordering below 115 K. Magnetization measurements on the parent Co3O2BO3 and Fe3O2BO3 compounds have been done for comparison. In Fe3O2BO3 the anisotropy of the different phases has been determined, showing that the anisotropy axis changes from the a to the b axis in the low-temperature antiferromagnetic phase. High magnetic uniaxial anisotropy has been detected for both Co3O2BO3 and Co2.25Fe0.75O2BO3. From the angle-dependent magnetization measurements it is found that in both compounds the easy axis of magnetization is the b [010] axis, where an antiferromagnetic component is superimposed on the main ferromagnetic component. In the c direction the behavior is purely antiferromagnetic. In Co2.25Fe0.75O2BO3 a strong reduction of the remanent magnetization and a very strong increase in coercive field along the b axis with respect to those found in Co3O2BO3 were observed from magnetic hysteresis cycles measured below T-C. The increase of coercive field is caused by the increase of defects upon Co substitution by Fe.
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