N. A. Nikolaev
Russian Academy of Sciences
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Featured researches published by N. A. Nikolaev.
Journal of Alloys and Compounds | 2001
I.S. Gladkaya; T. I. Dyuzheva; E.A. Ekimov; N. A. Nikolaev; N. A. Bendeliani
Abstract Different crystal growth methods were used to obtain single crystals of interstitial phases based on the α-boron structure in the B–O and B–C–O systems at pressures of 3–7 GPa and temperatures of 1500–2000 K. Boron suboxide carbide B(C,O)0.16 crystals with sizes up to 250 μm, suitable for complete structure analysis, were prepared by chemical reaction between B4C and B2O3 (molar ratio 1:1). The hexagonal unit cell parameters of the B(C,O)0.16 compound are: a=5.618(1) A, c=12.122(1) A, c/a=2.158, Z=38.54 and space group R 3 m. The analytical method for estimation of the chemical composition and the number of atoms per unit cell is presented for this kind of compound.
Journal of Alloys and Compounds | 1995
T. I. Dyuzheva; N. A. Bendeliani; L.N. Dzhavadov; Tat’yana N. Kolobyanina; N. A. Nikolaev
Abstract Phase relations in the Mg2SnSn system were studied by differential thermal analysis at a pressure of 5.8 GPa and temperatures up to 1100 °C. A schematic p, T diagram for Mg2Sn is presented. Single crystals of the high-pressure phase of Mg2Sn were obtained by growth from a molten solution under high pressure. Crystal data for Mg2Sn II were determined using a Buerger precession X-ray camera. The phase Mg2Sn II crystallizes with hexagonal unit cell, a = 13.19 ± 0.01 A , c = 13.28 ± 0.01 A , c/a = 1.006, D m = 4.1 ± 0.2 g cm −3 , z = 30, D c = 4.17 g cm −3 , space group P3c1 (no. 158) or P 3 c1 (no. 163).
Inorganic Materials | 2014
L. F. Kulikova; L. M. Lityagina; I.P. Zibrov; T. I. Dyuzheva; N. A. Nikolaev; V. V. Brazhkin
Phase transitions of the GeX2 (X = S, Se) dichalcogenides have been studied at pressures of up to p ≃ 8 GPa and temperatures from 675 to 1375 K, and portions of their p-T phase diagrams have been constructed using our and previous experimental data. The crystal structure of the GeS2-III phase has been refined by the Rietveld method (HgI2 structure, P42/nmc, a = 3.46906(2) Å, c = 10.9745(1) Å, Z = 2, Dx = 3.438 g/cm3, R = 0.06). GeSe2-III crystals have been grown for the first time at p ≃ 7 GPa in the temperature range 875–1275 K. The unit-cell parameters of GeSe2-III (hex) are a = 6.468 ± 0.004 Å and c = 24.49 ± 0.10 Å (Dmeas = 5.16 g/cm3, Dx = 5.18 g/cm3, Z = 12).
Crystallography Reports | 2006
T. I. Dyuzheva; L. M. Lityagina; N. A. Nikolaev; B. N. Martynov; N. A. Bendeliani
Single crystals of the high-pressure ɛ-FeOOH phase are grown from an aqueous solution at p = 7 GPa in the temperature range 580–350°C. Dark brown crystals of prismatic habit are obtained that have characteristic sizes of 0.1 × 0.1 × 0.7 mm. A region of the t-x phase diagram of the H2O-Fe2O3 system at p = 7 GPa is constructed on the basis of the data obtained.
Jetp Letters | 2014
N. B. Bolotina; V. V. Brazhkin; T. I. Dyuzheva; Yoshinori Katayama; L. F. Kulikova; L. V. Lityagina; N. A. Nikolaev
At normal pressure, the As2S3 compound is the most stable equilibrium modification with unique layered structure. The possibility of high-pressure polymorphism of this substance remains questionable. Our research showed that the As2S3 substance was metastable under pressures P > 6 GPa decomposing into two high-pressure phases: As2S3 → AsS2 + AsS. New AsS2 phase can be conserved in the single crystalline form in metastable state at room pressure up to its melting temperature (470 K). This modification has the layered structure with P1211 monoclinic symmetry group; the unit-cell values are a = 7.916(2) Å, b = 9.937(2) Å, c = 7.118(1) Å, β = 106.41° (Z = 8, density 3.44 g/cm3). Along with the recently studied AsS high-pressure modification, the new AsS2 phase suggests that high pressure polymorphism is a very powerful tool to create new layered-structure phases with “wrong” stoichiometry.
Crystallography Reports | 2013
N. B. Bolotina; V. V. Brazhkin; T. I. Dyuzheva; L. M. Lityagina; L. F. Kulikova; N. A. Nikolaev; I. A. Verin
AsS2 single crystals have been obtained for the first time from an As2S3 melt at pressures above 6 GPa and temperatures above 800 K in the As2S3 → AsS + AsS2 reaction. The monoclinic structure of the new high-pressure phase is solved by X-ray diffraction analysis and compared to the structure of high-pressure AsS phase, which was studied previously.
Crystallography Reports | 2012
L. F. Kulikova; T. I. Dyuzheva; N. A. Nikolaev; V. V. Brazhkin
The technique and results of the hydrothermal single-crystal growth of the high-pressure phase B2O3 II are described. Transparent colorless crystals 450 × 450 × 150 μm in size have been grown under hydrothermal conditions (pressure 5 GPa, temperature range 1425–1025 K, and cooling rate ∼100 K/h).
Journal of Crystal Growth | 2001
L. M. Lityagina; T. I. Dyuzheva; N. A. Nikolaev; N. A. Bendeliani
Crystallography Reports | 1998
T. I. Dyuzheva; L. M. Lityagina; N. A. Bendeliani; N. A. Nikolaev; G. I. Dorokhova
Journal of Alloys and Compounds | 2015
L. M. Lityagina; L. F. Kulikova; I.P. Zibrov; T. I. Dyuzheva; N. A. Nikolaev; V.V. Brazhkin