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Formation of two crystal modifications of Fe 7 C 3− x at 5.5 GPa
Author(s) -
Gromilov Sergey,
Chepurov Anatoly,
Sonin Valeri,
Zhimulev Egor,
Sukhikh Aleksandr,
Chepurov Aleksei,
Shcheglov Dmitry
Publication year - 2019
Publication title -
journal of applied crystallography
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.429
H-Index - 162
ISSN - 1600-5767
DOI - 10.1107/s1600576719013347
Subject(s) - carbide , diamond , materials science , diamond anvil cell , crystallography , crystal (programming language) , high pressure , phase (matter) , carbon fibers , diffraction , single crystal , metal , analytical chemistry (journal) , synthetic diamond , crystal structure , metallurgy , chemistry , thermodynamics , composite material , optics , composite number , physics , organic chemistry , chromatography , computer science , programming language
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 Fe 3 C is a normal run product, but the pressure at which Fe 7 C 3 carbide becomes stable is a subject of discussion. This paper demonstrates the synthesis of Fe 7 C 3 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 Fe 7 C 3 carbide was synthesized. This means that both carbides (Fe 7 C 3 and Fe 3 C) are stable at 5.5 GPa. Two crystal phases are described, Fe 14 C 6 and Fe 28 C 12− x . Fe 14 C 6 is based on the well known rhombic structure of Fe 7 C 3 , while Fe 28 C 12− x has a different packing order of Fe 6 C 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.