[en] At ambient pressure the solubility of magnesium in iron is very limited (of the order of 0.025 at.% in the liquid state), and vice versa. In a series of experiments using the piston-cylinder and multi-anvil apparatus at pressures up to 20 GPa and temperatures up to 2000 deg. C, we found an increase in the solid solubility of magnesium in iron up to 4 at.% Mg. The solution of magnesium in the bcc-structured Fe-based alloy increases the lattice parameter by approximately 2.4% with respect to that of pure iron

[en] We have measured the pressure-volume (P-V) relations for cubic iron-nickel alloys for three different compositions: Fe_0.64 Ni_0.36 , Fe_0.55 Ni_0.45 , and Fe_0.20 Ni_0.80 . It is observed that for a certain pressure range the bulk modulus does not change or can even decrease to some minimum value, after which it begins to increase under still higher pressure. In our experiment, we observe for the first time a new effect, namely, that the Fe-Ni alloys with high Ni concentrations, which show positive thermal expansion at ambient pressure, become Invar system upon compression over a certain pressure range

[en] A bulk composite superhard material was synthesized from graphitelike BC₃ at 20 GPa and 2300 K using a multianvil press. The material consists of intergrown boron carbide B₄C and B-doped diamond with 1.8 at.%B. The material exhibits semiconducting behavior and extreme hardness comparable with that of single-crystal diamond

[en] Diamond anvil cell (DAC) technique relies on pressure determination based on use of pressure gauges. Fluorescence-based gauges, such as ruby and Sm doped yttrium aluminum garnet (Sm:YAG), are frequently used in the high pressure research. Here we present the results of DAC experiments which allowed extending calibration curves of the fluorescence frequency versus pressure up to 120 GPa at high temperatures up to 700 K for both for ruby and Sm:YAG. Cubic boron nitride was used as the reference gauge.

[en] The densest boron phase (2.52 g cm^-3) was produced as a result of the synthesis under pressures above 9 GPa and temperatures up to ∼1800 deg. C. The x-ray powder diffraction pattern and the Raman spectra of the new material do not correspond to those of any known boron phases. A new high-pressure high-temperature boron phase was defined to have an orthorhombic symmetry (Pnnm (No. 58)) and 28 atoms per unit cell.

[en] Being a material of choice for lightweight armor applications, boron carbide has been intensively studied. Its behavior under pressure was investigated using both theoretical and experimental methods, such as powder X-ray diffraction and vibrational spectroscopy. As there is a discrepancy in experimental observations, in the presented work we studied vibrational properties of commercially available, ''nearly stoichiometric'' B₄C using IR and Raman spectroscopy up to 73 GPa. No phase transitions were found in the entire pressure range. Our results are at odds with the recent report of a phase transition in B_4.3C at about 40 GPa. (copyright 2017 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim)

[en] We have heated ferropericlase (Mg_0.80Fe_0.20)O to temperatures of over 2300 K at pressures of above 100 GPa to investigate the stability of the solid solution at elevated P, T conditions. The in situ X-ray study in laser-heated diamond anvil cells, as well as X-ray powder diffraction and chemical analysis of recovered samples, show that ferropericlase dissociates to magnesium oxide and ferrous oxide rich components. We demonstrate the importance of the combination of different analytical techniques for studies of solid-state chemical processes at extreme conditions

[en] A pressure gauge is a key issue of any high pressure experiment in a diamond anvil cell (DAC). Here we present a method of in situ synthesis of microcrystals of diamond that can be further used as a pressure standard in the course of the same DAC experiment. Calibration curve of the Raman shift versus pressure is extended up to 270 GPa and experimental results are compared with those of ab initio calculations.

[en] Owing to its outstanding elastic properties, the nitride spinel γ‐Si${}_3$N${}_4$ is of considered interest for materials scientists and chemists. DFT calculations suggest that Si${}_3$N${}_4$‐analog beryllium phosphorus nitride BeP${}_2$N${}_4$ adopts the spinel structure at elevated pressures as well and shows outstanding elastic properties. Herein, we investigate phenakite‐type BeP${}_2$N${}_4$ by single‐crystal synchrotron X‐ray diffraction and report the phase transition into the spinel‐type phase at 47 GPa and 1800 K in a laser‐heated diamond anvil cell. The structure of spinel‐type BeP${}_2$N${}_4$ was refined from pressure‐dependent in situ synchrotron powder X‐ray diffraction measurements down to ambient pressure, which proves spinel‐type BeP${}_2$N${}_4$ a quenchable and metastable phase at ambient conditions. Its isothermal bulk modulus was determined to 325(8) GPa from equation of state, which indicates that spinel‐type BeP${}_2$N${}_4$ is an ultraincompressible material. (© 2019 The Authors. Published by Wiley-VCH Verlag GmbH & Co. KGaA.)

[en] A nitrogen-rich compound, ReN₈.xN₂, was synthesized by a direct reaction between rhenium and nitrogen at high pressure and high temperature in a laser-heated diamond anvil cell. Single-crystal X-ray diffraction revealed that the crystal structure, which is based on the ReN₈ framework, has rectangular-shaped channels that accommodate nitrogen molecules. Thus, despite a very high synthesis pressure, exceeding 100 GPa, ReN₈.xN₂ is an inclusion compound. The amount of trapped nitrogen (x) depends on the synthesis conditions. The polydiazenediyl chains [-N=N-]_∞ that constitute the framework have not been previously observed in any compound. Ab initio calculations on ReN₈.xN₂ provide strong support for the experimental results and conclusions. (copyright 2018 Wiley-VCH Verlag GmbH and Co. KGaA, Weinheim)