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Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Krylov A. S., Krylova S. N., Laptash N. M., Vtyurin A. N.
Заглавие : Raman scattering study of temperature induced phase transitions in crystalline ammonium heptafluorozirconate, (NH4)3ZrF7
Место публикации : Vib. Spectrosc.: Elsevier Science BV, 2012. - Vol. 62. - P.258-263. - ISSN 0924-2031, DOI 10.1016/j.vibspec.2012.07.003
Примечания : Cited References: 31. - This work was partly supported by integration project SB RAS No 28, Russian Foundation for Basic Research project No 11-02-98002-r_siberia, No 12-02-00056, SS-4828.2012.2. The authors are grateful to Dr. I.N. Flerov for helpful discussions. The assistance of Dr. S. Skokov is sincerely appreciated.
Предметные рубрики: VIBRATIONAL-SPECTRA
X-RAY
DISORDER
DIFFRACTION
ELPASOLITE
SYMMETRY
RB2KSCF6
IF7
Ключевые слова (''Своб.индексиров.''): raman spectroscopy--phase transition--ammonium heptafluorozirconate--low temperature
Аннотация: This paper reports on a Raman spectroscopy investigation of phase transitions in (NH4)3ZrF7 crystal. Raman spectra were obtained and analyzed in a wavenumber range from 3800 to 15 cm−1 and in the temperature range from 7 to 360 K. The anomalies caused by a series of subsequent structural phase transitions have been analyzed. A soft phonon mode restoring in the distorted phase was found. The spectral changes observed in the current study are similar to those typically found in phase transitions near a tricritical point. The spectral changes in the middle wavenumber range, 700–150 cm−1, indicate that the phase transitions are due to structural ordering of pentagonal ZrF73− bipyramids. Spectral data also show that a phase transition near 225 K is accompanied by an increase of the unit cell volume. In addition, spectral changes in the range of internal vibrations of ammonium ions indicate that the ion's motion slows down with decrease of temperature.
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Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Prodaivoda G. T., Aleksandrov K. S., Vyzhva S. A., Nazarenko L. V.
Заглавие : Computation of effective elastic constants in anisotropic microseamy rocks
Место публикации : Geol. Geofiz. - 2000. - Vol. 41, Is. 3. - P.436-449. - ISSN 0016-7886
Примечания : Cited References: 25
Предметные рубрики: WAVE-PROPAGATION
SYMMETRY
Ключевые слова (''Своб.индексиров.''): anisotropy--modeling--orientation of microcracks--elastic waves
Аннотация: A generalized method of conditional moments for computation of effective elastic constants of anisotropic rocks with spatially oriented microcracks is considered. The method involves an additional operation of averaging of known solution data for a modeled rock of orthorhombic structure with ellipsoidal microcracks whose semiaxes are oriented along the coordinate axes. The averaging is performed using the distribution function of rock microcrack orientations, which is expanded into a series in terms of generalized spherical functions. The expansion coefficients are determined by an experiment. In calculating the effective elastic constants of anisotropic rocks, there are no constraints on the concentration of microcracks. We have studied the parameters of azimuthal anisotropy of elastic-wave velocities in modeled amphibolites with ellipsoidal hornblende grains oriented along the coordinate axes and with three-planar and spatially oriented systems of microcracks. The obtained results agree with experimental data of ultrasonic determinations of elastic constants for amphibolite samples.
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Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Aleksandrov K. S.
Заглавие : Phase-transitions and distortions of the structure in the family of crystals related to alpha-k2so
Место публикации : Kristallografiya. - 1993. - Vol. 38, Is. 1. - P.128-139. - ISSN 0023-4761; Crystallogr. Rep.
Примечания : Cited References: 38
Предметные рубрики: X-RAY
EXPECTED STRUCTURES
A2BX4 COMPOUNDS
TEMPERATURE
(NH4)2BEF4
CHEMISTRY
DISORDER
SYMMETRY
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Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Zhu J., Xia, Zhiguo, Zhang Y., Molokeev M. S., Liu Q.
Заглавие : Structural phase transitions and photoluminescence properties of Eu3+ doped Ca(2-x)BaxLaNbO6 phosphors
Место публикации : Dalton Trans.: Royal Society of Chemistry, 2015. - Vol. 44, Is. 42. - P.18536-18543. - ISSN 1477-9226, DOI 10.1039/c5dt03430b
Примечания : Cited References: 27. - The present work was supported by the National Natural Science Foundation of China (Grant No. 51272027, 51472028 and 51272242), Natural Science Foundations of Beijing (2132050), the Program for New Century Excellent Talents in the University of the Ministry of Education of China (NCET-12-0950), Beijing Nova Program (Z131103000413047), Beijing Youth Excellent Talent Program (YETP0635), and the Funds of the State Key Laboratory of New Ceramics and Fine Processing, Tsinghua University (KF201306)
Предметные рубрики: Double-perovskite
Luminescence properties
Thermal-stability
Crystal-chemistry
Red phosphors
White LEDs
Symmetry
Band
Ta
Ln
Аннотация: Crystal structures of the series of double perovskites Ca(2-x)BaxLaNbO6:Eu3+ phosphors have been examined by powder X-ray diffraction and Rietveld refinements. Ca2LaNbO6 has a monoclinic (P21/n) and Ba2LaNbO6 has a monoclinic (C2/m) structure. The structural phases of Ca(2-x)BaxLaNbO6:Eu3+ samples are divided into three sections depending on different Ca/Ba ratios: (1) monoclinic phase (P21/n) as Ca2LaNbO6 in the range of x = 0-0.1, (2) mixed phases containing Ca2LaNbO6 and Ba2LaNbO6 between 0.15 and 1.2, and (3) monoclinic phase (C2/m) as Ba2LaNbO6 for x = 1.4-2. Eu3+ ions act as the structural probes to study the structural phase transitions, and the evolution of the photoluminescence properties and thermal stability behaviours has been also comparatively investigated depending on different structural symmetries from Ca2LaNbO6 to Ba2LaNbO6 phase. The strong red emission from 5D0-7F2 peaking at 618 nm can be found in Ca2LaNbO6:Eu3+ phosphors, which is attributed to the low crystal field effect of the activator ions located in the highly distorted [Lao8] polyhedra sites. The composition-optimized phosphors can find applications in white light emitting diodes (LEDs).
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Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Pankrats A. I., Sablina K. A., Eremin M., Balaev A. D., Kolkov M., Tugarinov V. I., Bovina A. F.
Заглавие : Ferromagnetism and strong magnetic anisotropy of the PbMnBO4 orthoborate single crystals
Место публикации : J. Magn. Magn. Mater.: Elsevier, 2016. - Vol. 414. - P.82-89. - ISSN 0304-8853, DOI 10.1016/j.jmmm.2016.04.042
Примечания : Cited References: 20. - We acknowledge the assistance of A. Dubrovsky in magnetic measurements.This work was supported by the Russian Foundation for Basic Research, Projects nos. 13-02-00897 and 16-02-00563. MVE thanks for support the Russian Government Program of Competitive Growth of the Kazan Federal University, decision no. 930_p, May 22, 2015.
Предметные рубрики: PbMBO4 M
Resonance
Symmetry
Mn
Fe
Cr
Ключевые слова (''Своб.индексиров.''): strong ferromagnetic anisotropy--ferromagnetic resonance--exchange interactions
Аннотация: The PbMnBO4 orthoborate single crystals were first grown and their magnetic properties and ferromagnetic resonance were studied. It was found that the ferromagnetic state below the Curie temperature TC=31 K is characterized by the strong magnetic anisotropy. The significant effective anisotropy fields of PbMnBO4 determine the energy gap in the FMR spectrum, which is extraordinary large for ferromagnets (112 GHz at T=4.2 K). It was shown that the static Jahn-Teller effect characteristic of the Mn3+ ion leads to both the ferromagnetic ordering and the strong magnetic anisotropy in the crystal. In the strong external magnetic field the induced ferromagnetic ordering is retained in the crystal above the Curie temperature up to the temperatures multiply higher than TC. A weak anomaly of the dielectric permittivity was observed in PbMnBO4 at the Curie temperature at which the long-range ferromagnetic order is established. © 2016 Elsevier B.V. All rights reserved.
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Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Ovchinnikov S. G., Shneyder E. I.
Заглавие : The Interplay of Phonon and Magnetic Mechanism of Pairing in Strongly Correlated Electron System of High-T-c Cuprates
Коллективы :
Разночтения заглавия :авие SCOPUS: The interplay of phonon and magnetic mechanism of pairing in strongly correlated electron system of high-T c cuprates
Место публикации : J. Supercond. Nov. Magn.: SPRINGER, 2010. - Vol. 23, Is. 5. - P733-736. - ISSN 1557-1939, DOI 10.1007/s10948-009-0633-z
Примечания : Cited References: 26. - This work is supported by the Presidium RAS program N 7 "Quantum physics of condensed matter," the integration project SORAN-UrORAN N 40, and the RFFI Grant 09-02-00127.
Предметные рубрики: PHASE-TRANSITIONS
OXIDE SUPERCONDUCTORS
SYMMETRY
COPPER
MODEL
BAND
BI2SR2CACU2O8+DELTA
LA2-XSRXCUO4
PB
Ключевые слова (''Своб.индексиров.''): high-t-c superconductivity--strong correlated electron systems--mechanisms of superconducting pairing--high-t c superconductivity--mechanisms of superconducting pairing--strong correlated electron systems--ab initio--buckling mode--correlated electron systems--critical temperatures--cuprates--fitting parameters--high-t--isotope effect--low energies--magnetic mechanisms--order of magnitude--phonon mode--strongly correlated electron system--strongly correlated electrons--superconducting pairing--superconductivity mechanism--type theory--buckling--copper compounds--electrons--isotopes--magnetic materials--phonons--superconductivity--superconducting magnets
Аннотация: We consider magnetic mechanism of superconducting pairing in the effective low energy t - t' - t '' - J* model with all parameters calculated ab initio. Interaction of strongly correlated electrons with different phonon modes is also incorporated. In a BCS type theory, the d(x2-y2) gap is given by a sum of magnetic and phonon contributions. The main contribution to the only fitting parameter G is determined by a competition of the breathing and buckling modes. Fitting the parameter G from the isotope effect, we obtain that magnetic and phonon contributions to the critical temperature T-c work together and are of the same order of magnitude.
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Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Mel'nikova S. V., Laptash N. M., Zhogal' A. L.
Заглавие : Phase transitions in the oxyfluoride (NH4)(3)NbOF6
Разночтения заглавия :авие SCOPUS: Phase transitions in the oxyfluoride (NH4)3NbOF 6
Место публикации : Phys. Solid State: MAIK NAUKA/INTERPERIODICA/SPRINGER, 2007. - Vol. 49, Is. 5. - P958-962. - ISSN 1063-7834, DOI 10.1134/S1063783407050253
Примечания : Cited References: 11
Предметные рубрики: RAY-DIFFRACTION INVESTIGATIONS
DISTORTED PHASES
SYMMETRY
DISORDER
CRYSTAL
Аннотация: (NH4)(3)NbOF6 single crystals were grown, polarization-optical studies were performed, and birefringence was measured over the temperature range 90-500 K. A sequence of first-order structural phase transitions was found at temperatures T (1 down arrow) = 259.7 K and T (2 down arrow) = 257.7 K with temperature hysteresis delta T-1 = 0.9 K and delta T-2 = 1.9 K. The transitions are accompanied by twinning and the following change in the crystal symmetry: cubic paired left right arrows tetragonal paired left right arrows monoclinic. Optical second harmonic generation is found to occur at room temperature, which indicates that the cubic phase is not centrosymmetric. It is assumed that the phase transitions are ferroelastic and ferroelectric in nature.
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Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Korshunov M. M., Ovchinnikov S. G., Sherman A. V.
Заглавие : Effective Hamiltonian and the properties of normal and superconductive phases of n-type cuprates
Место публикации : Physica B: ELSEVIER SCIENCE BV, 2005. - Vol. 359: International Conference on Strongly Correlated Electron Systems (SCES 04) (JUL 26-30, 2004, Karlsruhe, GERMANY). - P521-523. - ISSN 0921-4526, DOI 10.1016/j.physb.2005.01.134
Примечания : Cited References: 13
Предметные рубрики: MODEL
SYMMETRY
Ключевые слова (''Своб.индексиров.''): strong electron correlations--superconductivity--multiband p-d model--n-type cuprates--multiband p-d model--n-type cuprates--strong electron correlations--superconductivity--antiferromagnetism--correlation theory--fermi surface--hamiltonians--mathematical models--microscopic examination--oxide superconductors--phase diagrams--semiconductor doping--generalized tight-binding (gtb)--multiband p-d models--n-type cuprates--single electron correlations--superconductivity
Аннотация: In the framework of the effective low-energy model for high-T-c, cuprates with account for three-center interaction terms and spin fluctuations the properties of normal and superconducting phases of n-type cuprates are investigated. Microscopic model parameters were obtained from ARPES data in undoped compounds. Obtained evolution of the chemical potential with doping, Fermi surface at optimal doping, and T-c(x) phase diagram are in remarkably good agreement with the experiment. (c) 2005 Elsevier B.V. All rights reserved.
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Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Komogortsev S. V., Iskhakov R. S.
Заглавие : Magnetization curve and magnetic correlations in a nanochain of ferromagnetic grains with random anisotropy
Место публикации : Phys. Solid State: AMER INST PHYSICS, 2005. - Vol. 47, Is. 3. - P495-501. - ISSN 1063-7834, DOI 10.1134/1.1884711
Примечания : Cited References: 31
Предметные рубрики: NANOCRYSTALLINE FERROMAGNETS
AMORPHOUS FERROMAGNETS
FIELD
MODEL
MICROSTRUCTURE
SIMULATIONS
DEPENDENCE
SYMMETRY
SYSTEM
MEDIA
Аннотация: The magnetization curve and magnetization correlation function are calculated for a ferromagnetic chain of single-domain nanoparticles with a randomly oriented anisotropy axis for different ratios between the exchange correlation and anisotropy energies. It is shown that the coercive force decreases as the exchange correlations increase. For strong exchange correlations, the magnetization curve is described by the following three successive magnetization processes as the applied field is increased: (i) nonuniform rotation of the magnetization of stochastic domains, (ii) collapse of the magnetic solitons, and (iii) nonuniform rotation of exchange-correlated magnetization vectors of the nanoparticles. For high fields, the calculated correlation function of the transverse magnetization components coincides with that predicted from linear theory. At low and zero fields, the main parameters of the correlation function (the variance and correlation radius) tend to certain finite values rather than diverge (as is the case in linear theory). The irreversible variation in the magnetization at low fields (the hysteresis loop) and the hysteresis of the main parameters of the correlation function are calculated. (c) 2005 Pleiades Publishing, Inc.
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10.

Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Gavrichkov V. A., Korshunov M. M., Ovchinnikov S. G.
Заглавие : Doping dependent electronic structure of cuprates and the effective low energy Hamiltonian for the magnetic pairing
Коллективы : International Conference on New Theories, Discoveries and Applications of Superconductors and Related Materials
Место публикации : Int. J. Mod. Phys. B/ International Conference on New Theories, Discoveries and Applications of Superconductors and Related Materials (5 ; 2004 ; June ; 11-16 ; Chongqing, China). - 2005. - Vol. 19, Is. 1-3. - P.247-249. - ISSN 0217-9792, DOI 10.1142/S0217979205028335
Примечания : Cited References: 14
Предметные рубрики: COPPER OXIDES
SYMMETRY
MODEL
Ключевые слова (''Своб.индексиров.''): electronic structure--strong electron correlations--magnetic mechanism of pairing--electronic structure--magnetic mechanism of pairing--strong electron correlations--copper derivative--calculation--chemical reaction--chemical structure--conference paper--correlation analysis--electron--electronics--energy--hybridization--intermethod comparison--magnetism--mathematical analysis--mathematical model
Аннотация: The properties of the normal and superconducting phases of p- and n-type cuprates are investigated in the appropriate low-energy models in the approximation beyond Hubbard I considering spin fluctuations. Calculated chemical potential dependence on doping, Fermi surface and T,(x) phase diagram for n-type cuprates are in remarkably good agreement with the experimental ones. Comparison of the singlet-triplet t-J model with simple t-J model shows that the spin-exciton mechanism originated from singlet-triplet hybridization leads to small contribution to the T-c(x) - optimal doping value becomes slightly lower and the maximum value of T-c become slightly higher.
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