TY - JOUR

T1 - Formation of two crystal modifications of Fe7C3-x at 5.5 GPa

AU - Gromilov, Sergey

AU - Chepurov, Anatoly

AU - Sonin, Valeri

AU - Zhimulev, Egor

AU - Sukhikh, Aleksandr

AU - Chepurov, Aleksei

AU - Shcheglov, Dmitry

PY - 2019/12/1

Y1 - 2019/12/1

N2 - The Fe-C system, which is widely used to grow commercial high-pressure-high-temperature diamond monocrystals, is rather complicated due to the formation of carbides. The carbide Fe3C is a normal run product, but the pressure at which Fe7C3 carbide becomes stable is a subject of discussion. This paper demonstrates the synthesis of Fe7C3 carbide and its detailed study using single-crystal and powder X-ray diffraction, as well as electron probe micro-analysis and scanning electron microscopy. The experiments were performed using a multiple-anvil high-pressure apparatus of 'split-sphere' (BARS) type at a pressure of 5.5 GPa and a temperature of 1623 K. Our results show that in the Fe-C system, in addition to diamond, a phase that corresponds to the Fe7C3 carbide was synthesized. This means that both carbides (Fe7C3 and Fe3C) are stable at 5.5 GPa. Two crystal phases are described, Fe14C6 and Fe28C12-x. Fe14C6 is based on the well known rhombic structure of Fe7C3, while Fe28C12-x has a different packing order of Fe6C polyhedrons. The results obtained in this study should be taken into account when synthesizing and growing diamond at high pressures and temperatures in metal-carbon systems with a high iron content, as well as when conducting experimental studies on the synthesis of diamond directly from carbide.

AB - The Fe-C system, which is widely used to grow commercial high-pressure-high-temperature diamond monocrystals, is rather complicated due to the formation of carbides. The carbide Fe3C is a normal run product, but the pressure at which Fe7C3 carbide becomes stable is a subject of discussion. This paper demonstrates the synthesis of Fe7C3 carbide and its detailed study using single-crystal and powder X-ray diffraction, as well as electron probe micro-analysis and scanning electron microscopy. The experiments were performed using a multiple-anvil high-pressure apparatus of 'split-sphere' (BARS) type at a pressure of 5.5 GPa and a temperature of 1623 K. Our results show that in the Fe-C system, in addition to diamond, a phase that corresponds to the Fe7C3 carbide was synthesized. This means that both carbides (Fe7C3 and Fe3C) are stable at 5.5 GPa. Two crystal phases are described, Fe14C6 and Fe28C12-x. Fe14C6 is based on the well known rhombic structure of Fe7C3, while Fe28C12-x has a different packing order of Fe6C polyhedrons. The results obtained in this study should be taken into account when synthesizing and growing diamond at high pressures and temperatures in metal-carbon systems with a high iron content, as well as when conducting experimental studies on the synthesis of diamond directly from carbide.

KW - carbides

KW - diamond

KW - growth from melt

KW - high-pressure techniques

KW - X-ray diffraction

KW - DIAMOND CRYSTALLIZATION

KW - SYSTEM

KW - CARBON

KW - IRON CARBIDE

KW - HIGH-TEMPERATURE

KW - S-C

KW - FE3C

KW - GROWTH

KW - GPA

UR - http://www.scopus.com/inward/record.url?scp=85075790543&partnerID=8YFLogxK

U2 - 10.1107/S1600576719013347

DO - 10.1107/S1600576719013347

M3 - Article

AN - SCOPUS:85075790543

VL - 52

SP - 1378

EP - 1384

JO - Journal of Applied Crystallography

JF - Journal of Applied Crystallography

SN - 0021-8898

ER -