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Dive into the research topics where N. A. Nikolaev is active.

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Featured researches published by N. A. Nikolaev.


Journal of Alloys and Compounds | 2001

Crystal growth at high pressure and the problem of characterization of the interstitial phases in the B–C–O system

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

Crystal growth of the high-pressure phase of Mg2Sn

T. I. Dyuzheva; N. A. Bendeliani; L.N. Dzhavadov; Tat’yana N. Kolobyanina; N. A. Nikolaev

Abstract Phase relations in the Mg2SnSn 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

High-pressure, high-temperature study of GeS2 and GeSe2

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

Growth of single crystals of the high-pressure ɛ-FeOOH phase

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

High-pressure polymorphism of As2S3 and new AsS2 modification with layered structure

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

Crystal structure of new AsS 2 compound

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

Single-crystal growth of the high-pressure phase B2O3 II

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

Hydrothermal crystal growth of stishovite (SiO2)

L. M. Lityagina; T. I. Dyuzheva; N. A. Nikolaev; N. A. Bendeliani


Crystallography Reports | 1998

Hydrothermal synthesis of coesite (SiO2)

T. I. Dyuzheva; L. M. Lityagina; N. A. Bendeliani; N. A. Nikolaev; G. I. Dorokhova


Journal of Alloys and Compounds | 2015

Structural transformations in the As–Se system under high pressures and temperatures

L. M. Lityagina; L. F. Kulikova; I.P. Zibrov; T. I. Dyuzheva; N. A. Nikolaev; V.V. Brazhkin

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T. I. Dyuzheva

Russian Academy of Sciences

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L. M. Lityagina

Russian Academy of Sciences

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N. A. Bendeliani

Russian Academy of Sciences

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L. F. Kulikova

Russian Academy of Sciences

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V. V. Brazhkin

Russian Academy of Sciences

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L.N. Dzhavadov

Russian Academy of Sciences

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N. B. Bolotina

Russian Academy of Sciences

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B. N. Martynov

Russian Academy of Sciences

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E.A. Ekimov

Russian Academy of Sciences

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