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Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Mel'nikova S. V., Pogoreltsev E. I., Flerov I. N., Laptash N. M.
Заглавие : Unusual sequence of phase transitions in (NH4)3TiF7 detected by optic and calorimetric studies
Коллективы : Russian Foundation for Basic Research [12-02-00056]; 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. 165. - P.14-19. - ISSN 0022-1139, DOI 10.1016/j.jfluchem.2014.05.016. - ISSN 1873-3328
Примечания : Cited References: 13. - This work was supported by Russian Foundation for Basic Research (Grant no. 12-02-00056), 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
DIFFRACTION
NH4F
Ключевые слова (''Своб.индексиров.''): cubic fluorides--phase transitions--crystal-optic--calorimetry
Аннотация: For the first time structural transformations were observed for one of the compounds belonging to the family of double salt fluorides A3MeF7 = A2MeF6·AF. Single crystals of (NH4)3TiF7 = (NH4)2TiF6·NH4F were grown by evaporation of the aqueous solution. Polarizing optical observations, heat capacity and birefringence Δn = (no − ne) measurements were performed in a wide temperature range 100–400 K. Two reversible, first order structural phase transitions were found to be followed by an unusual sequence of symmetry changes: cubic (G3) (T2↓ = 287.5 K; T2↑ = 291–310 K) ↔ P4/mnc (G2) (T1↓ = 358.5 K; T1↑ = 360 K) ↔ 4/m (G1). The twin structures observed were described assuming the existence of cubic parent phase G0 with P m 3 ¯ m symmetry.
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Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Pogorel'tsev E. I., Mel'nikova S. V., Kartashev A. V., Gorev M. V., Flerov I. N., Laptash N. M.
Заглавие : Thermal, optical, and dielectric properties of Fluoride Rb2TaF7
Коллективы : Russian Foundation for Basic Research, Government of Krasnoyarsk Territory, Krasnoyarsk Region Science and Technology Support Fund [16-42-243001]
Место публикации : Phys. Solid State: MAIK Nauka-Interperiodica / Springer, 2017. - Vol. 59, Is. 5. - P.986-991. - ISSN 1063-7834, DOI 10.1134/S1063783417050250. - ISSN 1090-6460(eISSN)
Примечания : Cited References:21. - The reported study was funded by the Russian Foundation for Basic Research, Government of Krasnoyarsk Territory, Krasnoyarsk Region Science and Technology Support Fund to the research project no. 16-42-243001.
Предметные рубрики: PHASE-TRANSITIONS
X-RAY
DISORDER
NMR
DIFFRACTION
OXYFLUORIDE
Аннотация: The thermal, optical, and dielectric properties of fluoride Rb2TaF7 were investigated. It was observed that the variation in chemical pressure in fluorides A2+TaF7 caused by the cation substitution of rubidium for ammonium does not affect the ferroelastic nature of structural distortions, but leads to stabilization of the high- and low-temperature phases and enhancement of birefringence. The entropy of the phase transition P4/nmm ↔ Cmma is typical of the shift transformations, which is consistent with a model of the initial and distorted phase structures. The anisotropy of chemical pressure causes the change of signs of the anomalous strain and baric coefficient dT/dp of Rb2TaF7 as compared with the values for its ammonium analog.
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Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Golovnev N. N., Molokeev M. S., Vereshchagin, Sergey N., Sterkhova I. V., Atuchin V. V.
Заглавие : The cis-trans isomer transformation, spectroscopic and thermal properties of Li, Na, K 1,3-diethyl-2-thiobarbiturate complexes
Коллективы : Ministry of Education and Science of the Russian Federation
Место публикации : Polyhedron: PERGAMON-ELSEVIER SCIENCE LTD, 2015. - Vol. 85. - P.493-498. - ISSN 0277-5387, DOI 10.1016/j.poly.2014.09.011
Примечания : Cited References:42. - The study has been carried out within the public task of the Ministry ofEducation and Science of the Russian Federation for research engineeringat the Siberian Federal University in 2014. V.V.A. is partly supportedby the Ministry of Education and Science of the Russian Federation.
Предметные рубрики: CRYSTAL-STRUCTURE
2-THIOBARBITURIC ACID
STRUCTURAL-CHARACTERIZATION
HYDROGEN-BOND
DIFFRACTION
THIOBARBITURATE
CHEMISTRY
NETWORKS
SPECTRA
SERIES
Ключевые слова (''Своб.индексиров.''): 1,3-diethyl-2-thiobarbituric acid--alkali ions--x-ray diffraction--infrared spectroscopy--thermal analysis
Аннотация: Three new complexes of 1,3-diethyl-2-thiobarbituric acid (C8H11N2O2S, HDETBA) with Li+, Na+, K+ alkali ions were synthesized. The complexes have been prepared by neutralization of 1,3-diethyl-2-thiobarbituric acid with the corresponding metal hydroxide in aqueous solution. The colorless crystals have been investigated using X-ray single crystal and powder techniques and characterized by differential scanning calorimetry, thermogravimetry and infrared spectroscopy. The compounds of MDETBA with M = Li and M = Na crystallize in the monoclinic lattice with a = 10.678(1) Å, b = 7.2687(9) Å, c = 13.202(2) Å, β = 108.841(2)°, Z = 4, V = 969.8(2) Å3, S.G. P21/n and a = 10.534(2) Å, b = 7.604(1) Å, c = 14.186(1) Å, β = 108.964(4)°, Z = 4, V = 1074.6(3) Å3, S.G. P21/n, respectively. Сompound KDETBA crystallizes in the orthorhombic lattice with a = 4.2541(6) Å, b = 14.739(2) Å, c = 16.635(3) Å, Z = 4, V = 1043.1(3) Å3, S.G. P212121. In Li(I) and Na(I) complexes, the DETBA− ion is in cis-configuration and, in the K(I) complex, this ion is in trans-configuration. The reason for the transformation from cis- to trans-configuration has been rationalized.
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Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Gorev M. V., Bondarev V. S., Raevskaya S. I., Ivliev M. P., Raevskii I. P., Flerov I. N.
Заглавие : Studies of the heat capacity and thermal expansion of the Na0.95K0.05NbO3 solid solution
Коллективы : Council on Grants from the President of the Russian Federation for Support of Leading Scientific Schools of the Russian Federation [NSh-4828.2012.2]; Russian Foundation for Basic Research [12-02-31799 mol_a]
Место публикации : Phys. Solid State: MAIK Nauka-Interperiodica / Springer, 2014. - Vol. 56, Is. 2. - P.367-372. - ISSN 1063-7834, DOI 10.1134/S1063783414020115. - ISSN 1090-6460
Примечания : Cited References: 27. - This study was supported by the Council on Grants from the President of the Russian Federation for Support of Leading Scientific Schools of the Russian Federation (grant no. NSh-4828.2012.2) and the Russian Foundation for Basic Research (project no. 12-02-31799 mol_a).
Предметные рубрики: SODIUM NIOBATE
PHASE-TRANSITIONS
TEMPERATURE-RANGE
SINGLE-CRYSTALS
KNBO3
FERROELECTRICS
DIFFRACTION
OCTAHEDRA
Аннотация: The heat capacity and thermal expansion of ceramic samples of the Na0.95K0.05NbO3 solid solution have been investigated over a wide temperature range of 100-750 K. The observed anomalies in the heat capacity and thermal expansion at T (4) = 297 K, T (3) = 535 K, T (2) = 665 K, and T (1) a parts per thousand 710 K correspond to the sequences of phase transitions N - Q - G - S - T1. It has been shown that, as a result of the phase transitions, the unit cell volume at T (4) and T (2) decreases, and at T (3) and T (1), increases with increasing temperature. The directions of the shift of the phase transition temperatures induced by hydrostatic pressure have been determined. It has been established that all structural transformations are accompanied by relatively small variations in the entropy. Different mechanisms of the structural distortions have been discussed.
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Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Atuchin V. V., Gavrilova T. A., Kesler V. G., Molokeev M. S., Aleksandrov K. S.
Заглавие : Structural and electronic parameters of ferroelectric K3WO3F3
Коллективы :
Место публикации : Solid State Commun. - 2010. - Vol. 150, Is. 43-44. - P.2085-2088. - ISSN 0038-1098, DOI 10.1016/j.ssc.2010.09.023
Примечания : Cited References: 34. - This study was partly supported by RFBR (Grant 09-02-00062) and SB RAS (Grant 34).
Предметные рубрики: CORE-LEVEL SPECTROSCOPY
PHASE-TRANSITIONS
RHEED ANALYSIS
SURFACE
OXYFLUORIDE
ELPASOLITE
(NH4)(2)KWO3F3
SUBSTITUTION
TEMPERATURE
DIFFRACTION
Ключевые слова (''Своб.индексиров.''): ferroelectrics--chemical synthesis--electronic structure--photoelectron spectroscopies
Аннотация: The low-temperature ferroelectric G2 polymorph of K3WO3F3 oxyfluoride is formed by chemical synthesis. The electronic parameters of G2-K3WO3F3 have been measured by X-ray photoelectron spectroscopy under excitation with Al K alpha radiation (1486.6 eV). Detailed spectra have been recorded for all element core levels and Auger lines. The chemical bonding effects in the WO3 F-3 and WO6 octahedrons are considered by using the binding energy difference Delta BE(O-W) = BE(O 1s) BE(W 4f(7/2)). (C) 2010 Elsevier Ltd. All rights reserved.
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Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Fischer P., Pomjakushin V., Sheptyakov D., Keller L., Janoschek M., Roessli B., Schefer J., Petrakovskii G. A., Bezmaternykh L. N., Temerov V. L., Velikanov D. A.
Заглавие : Simultaneous antiferromagnetic Fe3+ and Nd3+ ordering in NdFe3((BO3)-B-11)(4)
Разночтения заглавия :авие SCOPUS: Simultaneous antiferromagnetic Fe3+ and Nd3+ ordering in NdFe3(11BO3)4
Место публикации : J. Phys.: Condens. Matter: IOP PUBLISHING LTD, 2006. - Vol. 18, Is. 34. - P.7975-7989. - ISSN 0953-8984, DOI 10.1088/0953-8984/18/34/010
Примечания : Cited References: 20
Предметные рубрики: PHASE-TRANSITION
DIFFRACTION
CRYSTALS
GDFE3(BO3)(4)
SINQ
Ключевые слова (''Своб.индексиров.''): iron compounds--magnetic moments--magnetization--neodymium compounds--neutron diffraction--vectors--crystal-field effects--free ion moment--specific heat measurements--symmetry analysis--antiferromagnetic materials
Аннотация: By means of magnetic susceptibility and specific heat measurements, x-ray and unpolarized neutron diffraction investigations on powder and single-crystal samples, simultaneous long-range antiferromagnetic Fe and Nd ordering in NdFe3((BO3)-B-11)(4) with R32 chemical structure has been found at temperatures below T-N = 30.5(5) K down to 1.6 K. At temperatures down to 19 K the propagation vector is k(hex) = [0, 0, 3/2] and becomes slightly incommensurate at lower temperatures. Combined with symmetry analysis, best powder neutron profile fits are obtained with magnetic spiral configurations with the magnetic moments oriented parallel to the hexagonal basal plane according to the irreducible representations tau(3) in the commensurate case. This is in agreement with the easy directions of magnetization perpendicular to the c-axis as determined by magnetic susceptibility measurements. At 1.6 K the magnetic Fe moment amounts to 4.9 mu(B) B close to the free ion moment of Fe3+. The magnetic Nd3+ moment saturates presumably due to crystal-field effects at 2.7 mu(B).
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Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Sadreev A. F., Sukhinin Y. V.
Заглавие : Phase transitions in a system of CH3(CH2)(n-1) self-assembled on the Au(111) crystal surface
Место публикации : Phys. Rev. B: AMERICAN PHYSICAL SOC, 1996. - Vol. 54, Is. 24. - P17966-17973. - ISSN 1098-0121, DOI 10.1103/PhysRevB.54.17966
Примечания : Cited References: 44
Предметные рубрики: ORGANIZED MOLECULAR ASSEMBLIES
ALKYL THIOL MONOLAYERS
STRUCTURAL CHARACTERIZATION
DYNAMICS SIMULATION
DEVILS STAIRCASE
GOLD SURFACES
FILMS
MODEL
CHAIN
DIFFRACTION
Аннотация: The n-alkanethiols CH3(CH2)(n-1) on the crystal surface of gold (111) are considered. Couplings between atoms (C, H) of the n-alkanethiols were modelled by the Morse potential, and couplings between the n-alkanethiols and the crystal surface were modelled by 12-3 potentials. Because of symmetry Z(2) of the n-alkanethiols in a tilted state, the system can be reduced to the Ising model on the triangular lattice, the phase diagram of which can be explicitly considered. Depending on the choice of the coupling parameters, the ordered state of the system may form an incommensurate or 2X1 superstructure. The temperatures of the phase transition, equilibrium tilting, twisting, and azimuthal angles are found to depend on the Morse coupling constants.
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Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Likhacheva A. Y., Goryainov S. V., Krylov A. S., Bul'bak T. A., Prasad PSR
Заглавие : Raman spectroscopy of natural cordierite at high water pressure up to 5?GPa
Место публикации : J. Raman Spectrosc.: Wiley-Blackwell, 2012. - Vol. 43, Is. 4. - P.559-563. - ISSN 0377-0486, DOI 10.1002/jrs.3060
Примечания : Cited References: 38. - We greatly appreciate the critical comments of Prof. R. Kaindl and an anonymous reviewer on this work, and we thank Dr G. Lepezin for providing the cordierite sample. This work was supported by RFBR grant 11-05-01121-a.
Предметные рубрики: SINGLE-CRYSTAL STRUCTURE
X-RAY
CHANNEL H2O
BEHAVIOR
SPECTRA
CO2
POLYMORPHISM
DIFFRACTION
CHEMISTRY
CAVITIES
Ключевые слова (''Своб.индексиров.''): cordierite--raman spectroscopy--high pressure--phase transition
Аннотация: The high-pressure behaviour of cordierite, a widespread ring aluminosilicate with channels incorporating fluid compounds (H2O, CO2), is characterized by the absence of phase transitions up to 2.5 GPa. However, the distortion of the ring tetrahedra observed previously at 2.3 GPa is supposed to introduce a phase transition at higher pressure, which has not been checked so far. This work presents a high-pressure Raman spectroscopic study of natural cordierite compressed in water medium up to 4.7 GPa in a diamond anvil cell. At P 4 GPa, a disordering of both the framework and intrachannel H2O subsystem is apparent from significant broadening of Raman peaks and the evolution of short-range order parameters. This is followed by abrupt shifts of the framework and O–H stretching modes at about 4.5 GPa, indicating a first-order phase transition. Its reversibility is seen from the recovery of the initial spectrum at P 3 GPa. The shift amplitudes of different framework modes indicate the predominance of distortion over contraction of the framework polyhedra upon this transition. The disordering of the H2O subsystem in the high-pressure phase is likely a consequence of distortion of the channel-forming framework elements, which is supposed to be a driving force of this transition. Copyright © 2011 John Wiley & Sons, Ltd.
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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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10.

Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Zhang H., Yu T., Chen Z., Nelson C. S., Bezmaternykh L. N., Abeykoon A. M. M., Tyson T. A.
Заглавие : Probing magnetostructural correlations in multiferroic HoAl3(BO3)4
Место публикации : Phys. Rev. B: American Physical Society, 2015. - Vol. 92, Is. 10. - Ст.104108. - ISSN 1098, DOI 10.1103/PhysRevB.92.104108. - ISSN 1550235X(eISSN)
Примечания : Cited References:97. - This work is supported by the U.S.Department of Energy Grant No. DE-FG02-07ER46402. Synchrotron powder x-ray diffraction and x-ray absorption data acquisition were performed at Brookhaven National Laboratory's National Synchrotron Light Source (NSLS). Use of the NSLS was supported by the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences, under Contract No. DE-AC02-98CH10886. The Physical Properties Measurement System used in the heat capacity measurements was acquired under National Science Foundation Major Research Instrumentation Grant No. DMR-0923032 (American Recovery and Reinvestment Act award). This research used resources of the National Energy Research Scientific Computing Center, a U.S. Department of Energy Office of Science User Facility supported by the Office of Science of the U.S. Department of Energy under Contract No. DE-AC02-05CH11231.
Предметные рубрики: PAIR DISTRIBUTION FUNCTION
TOTAL-ENERGY CALCULATIONS
WAVE BASIS-SET
FERROELECTRIC POLARIZATION
DEBYE TEMPERATURES
SINGLE-CRYSTALS
HOFE3(BO3)4
GDFE3(BO3)4
DIFFRACTION
FEATURES
Аннотация: The system HoAl3(BO3)(4) has recently been found to exhibit a large magnetoelectric effect. To understand the mechanism, macroscopic and atomic level properties of HoAl3(BO3)(4) were explored by temperature and magnetic field dependent heat capacity measurements, pressure and temperature dependent x-ray diffraction measurements, as well as temperature and magnetic field dependent x-ray absorption fine structure measurements. The experimental work was complemented by density functional theory calculations. An anomalous change in the structure is found in the temperature range where large magnetoelectric effects occur. No significant structural change or distortion of the HoO6 polyhedra is seen to occur with magnetic field. However, the magnetic field dependent structural measurements reveal enhanced correlation between neighboring HoO6 polyhedra. This observed response is seen to saturate near 3 T. A qualitative atomic level description of the mechanism behind the large electric polarization induced by magnetic fields in the general class of RAl3(BO3)(4) systems (R = rare earth) is developed.
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