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1.

Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Mel'nikova S. V., Molokeev M. S., Laptash N. M., Misyul S. V.
Заглавие : A non-typical sequence of phase transitions in (NH4)3GeF7: optical and structural characterization
Коллективы : RFBR [15-02-02009 a]
Место публикации : Dalton Trans.: Royal Society of Chemistry, 2016. - Vol. 45, Is. 12. - P.5321-5327. - ISSN 1477-9226, DOI 10.1039/c5dt04907e. - ISSN 1477-9234(eISSN)
Примечания : Cited References:25. - The reported study was partially supported by RFBR, research project no. 15-02-02009 a
Предметные рубрики: Crystal-structure
Powder diffraction
NH4F
Fluorination
Аннотация: Single crystals of germanium double salt (NH4)3GeF7 = (NH4)2GeF6·NH4F = (NH4)3[GeF6]F were grown and studied by the methods of polarization optics and X-ray diffraction. The birefringence Δn = (no − ne), the rotation angle of the optical indicatrix ϕ(T) and unit cell parameters were measured in the temperature range 100–400 K. Three structural phase transitions were found at the temperatures: T1↓ = 279.2 K (T1↑ = 279.4 K), T2↑ = 270 K (T2↓ = 268.9 K), T3↓ = 218 K (T3↑ = 227 K). An unusual sequence of symmetry transformations with temperature change was established: P4/mbm (Z = 2) (G1) ↔ Pbam (Z = 4) (G2) ↔ P21/c (Z = 4) (G3) ↔ Pa (Z = 8) (G4). The crystal structures of different phases were determined. The experimental data were additionally interpreted by a group-theoretical analysis of the complete condensate of order parameters taking into account the critical and noncritical atomic displacements. Strengthening of the N–H⋯F hydrogen bonds can be a driving force of the observed phase transitions.
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2.

Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Aleksandrov K. S., Mel'nikova S. V., Kruglik A. I.
Заглавие : X-ray and optic investigations of phase-transition in cslicro4 crystal
Место публикации : Ferroelectrics: Gordon Breach SCI Publ LTD, 1988. - Vol. 81, Is. 1. - P.153-156. - ISSN 0015-0193, DOI 10.1080/00150198808008833
Примечания : Cited References: 2
Аннотация: The study of optical properties and X-ray investigations were carried out in CsLiCrO4crystal. It was found (is discussed) an unusual 4 temperature dependence of optical indicatrix rotation and monoclinic angles.
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3.

Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Mel'nikova S. V., Aleksandrov K. S., Anistratov A. T., Beznosikov B. V.
Заглавие : Birefringence and structural phase transitions in ABCl//3-type crystals
Место публикации : Sov. Phys. Solid State. - 1977. - Vol. 19, Is. 1. - P.18-20; Phys. Solid State
Ключевые слова (''Своб.индексиров.''): electrooptical effects--crystals
Аннотация: The refractive indices and birefringence of CsPbCl//3, TlMnCl//3, and CsSrCl//3 were determined a wide temperature range, which included phase transition points. Relatively high values of the photoelastic and acoustooptic characteristics were obtained: the th acoustooptic figure of merit M//2 was 12 multiplied by (times) 10** minus **1**8 cgs units for TlMnCl//3 and 98 multiplied by (times) 10** minus **1**8 cgs units for CsPbCl//3. A strong influence of partial Sr for Ca substitution on the properties and transition temperatures was observed. A phenomenological theory was used to analyze the relationship between the birefringence anomalies and the theromodynamic parameters of the transitions. A comparison was made with KMnF//3 and SrTiO//3.
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4.

Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Aleksandrov K. S., Anistratov A. T., Mel'nikova S. V., Zinenko V. I., Shabanova L. A., Beznosikov B. V.
Заглавие : Birefringence, twinning and structural phase transitions in ABCl3 single crystals
Коллективы : International meeting on ferroelectricity
Место публикации : Ferroelectrics. - 1978. - Vol. 20, Spesial issue. - P.305-307. - DOI 10.1080/00150197808237245
Аннотация: The temperature investigations of birefringence, twinning and elasticity of CsPbCl3, CsSrCl3, TlMnCl3, RbCdCl3, CsCaCl3 and RbMnCl3, were carried out. A group-theoretical analysis is made and the description of phase transitions is given.
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5.

Вид документа : Статья из сборника (однотомник)
Шифр издания :
Автор(ы) : Chekanova L. A., Denisova E. A., Mel'nikova S. V., Iskhakov R. S.
Заглавие : Composite magnetic materials based on porous templates with different pores morphology: synthesis and magnetic properties
Коллективы : Euro-Asian Symposium "Trends in MAGnetism": Nanomagnetism
Место публикации : V Euro-Asian simposium "Trend in MAGnetism": Nanomagnetism: abstracts. - Vladivostok: FEFU, 2013. - С. 169. - ISBN 978-5-7444-3124-2
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6.

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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7.

Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Pogoreltsev E. I., Mel'nikova S. V., Kartashev A. V., Molokeev M. S., Gorev M. V., Flerov I. N., Laptash N. M.
Заглавие : Ferroelastic phase transitions in (NH4)2TaF7
Место публикации : Phys. Sol. St.: Pleiades Publishing, 2013. - Vol. 55, Is. 3. - P.611-618. - DOI 10.1134/S1063783413030232
Аннотация: The heat capacity, unit cell parameters, permittivity, optical properties, and thermal expansion of the (NH4)2TaF7 compound with a seven coordinated anion polyhedron have been measured. It has been found that the compound undergoes two successive phase transitions with the symmetry change: tetragonal (T1 = 174 K) orthorhombic (T2 = 156 K) tetragonal. The ferroelastic nature of structural transformations has been established, and their entropy and susceptibility to hydrostatic pressure have been determined.
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8.

Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Flerov I. N., Kartashev A. V., Mel'nikova S. V.
Заглавие : Calorimetric and optical studies of orthorhombic and cubic CsLiCrO4 crystals
Разночтения заглавия :авие SCOPUS: Calorimetric and optical studies of orthorhombic and cubic CsLiCrO 4 crystals
Место публикации : Phys. Solid State: MAIK NAUKA/INTERPERIODICA/SPRINGER, 2006. - Vol. 48, Is. 11. - P2171-2176. - ISSN 1063-7834, DOI 10.1134/S1063783406110242
Примечания : Cited References: 23
Предметные рубрики: PHASE-TRANSITIONS
X-RAY
NH4LISO4
ALPHA
Аннотация: Careful calorimetric and polarization optical studies of a metastable cubic modification of a CsLiCrO4 crystal (space group (F43m)) are performed. Anomalies of the heat capacity indicative of structural distortions at 92.4 and 69.1 K were revealed, and the values of the thermodynamic parameters of the phase transitions were determined. The crystal twinning in the intermediate phase was studied. A comparative analysis of the phase transitions occurring in a series of ALiMO(4) crystals (A=NH4, Cs; M=S, Cr, Mo, W) was performed. First studies of the monotropic structural transformation F43m - Pmcn and the enantiotropic phase transition Pmcn reversible arrow P112(1)/n were carried out using scanning calorimetry, and the thermodynamic parameters of these transitions were determined.
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9.

Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Krylov A. S., Goryainov S. V., Laptash N. M., Vtyurin A. N., Mel'nikova S. V., Krylova S. N.
Заглавие : Influence of the molecular groups ordering on structural phase transitions in (NH4)2WO2F4 crystal
Место публикации : Cryst. Growth Des.: American Chemical Society, 2014. - Vol. 14, Is. 1. - P.374-380. - ISSN 1528-7483, DOI 10.1021/cg400899m. - ISSN 1528-7505
Примечания : Cited References: 27. - This work was partly supported by the Russian Foundation for the Basic Research project no. 12-02-00056, no. 13-02-00825, and integration project SB RAS no. 28, SS-4828.2012.2.Published as part of the Crystal Growth & Design virtual special issue Anion-controlled New Inorganic Materials.
Предметные рубрики: RAMAN-SCATTERING
NEUTRON-SCATTERING
SOLID-STATE
OXYFLUORIDES
DISORDER
POLAR
ANION
Аннотация: Phase transitions of the (NH4)2WO2F 4 crystal were studied by Raman spectroscopy in the range from 10 to 350 K. The mechanism of two phase transitions at T1 = 201 and T 2 = 160 K was proposed. The significant spectra changes occur in the range corresponding to the W-O vibrations. The first temperature phase transition is due to the ordering of the quasi-octahedral groups [WO 2F4]2- and partial ordering of ammonium groups. Experimental data allow for attributing the first (T1 = 201 K) phase transition to the first order close to the tricritical point. The noticeable changes of the Raman spectrum have been found in the range corresponding to the ammonium vibrations below the temperature T2. The second phase transition is associated with the further ordering of ammonium groups. Room temperature (296 K) experiments have been carried out under high hydrostatic pressure up to 10 GPa. Above 2 GPa, new spectral features appear, allowing for the assumption of the existence of a new high-pressure phase of (NH 4)2WO2F4, which is mainly connected with ordering of the [WO2F4]2- quasi-octahedral groups.
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10.

Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Bogdanov E. V., Pogoreltsev E. I., Mel'nikova S. V., Gorev M. V., Flerov I. N., Molokeev M. S., Kartashev A. V., Kocharova A. G., Laptash N. M.
Заглавие : Investigation into phase diagrams of the fluorine–oxygen system: ferroelastic–antiferroelectric (NH4)2WO2F4–(NH4)2MoO2F4
Место публикации : Phys. Sol. St.: Pleiades Publishing, 2013. - Vol. 55, Is. 2. - P.409-418. - DOI 10.1134/S1063783413020042
Аннотация: Thermal, physical, structural, optical, and dielectric investigations have been performed for oxy- fluoride solid solutions (NH4)2W1–xMoxO2F4 (x = 0, 0.1, 0.2, 0.3, 0.4, 0.6, 0.8, 1). The character of the influence of the chemical and hydrostatic pressures on the stability of the parent (space group Cmcm) and dis& torted ferroelastic and antiferroelectric phases has been determined by analyzing the temperature–pressure, unit cell volume–composition, and temperature–composition phase diagrams. The specific features of the nature and mechanism of the phase transitions have been discussed using the available data on the structural, entropy, and dielectric parameters.
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