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Structural evolution in boron nitrides during the hexagonal‐cubic phase transition under high pressure at high temperature
Author(s) -
He LianLong,
Akaishi Minoru,
Horiuchi Shigeo
Publication year - 1998
Publication title -
microscopy research and technique
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.536
H-Index - 118
eISSN - 1097-0029
pISSN - 1059-910X
DOI - 10.1002/(sici)1097-0029(19980215)40:4<243::aid-jemt1>3.0.co;2-t
Subject(s) - high resolution transmission electron microscopy , wurtzite crystal structure , crystallography , materials science , boron nitride , monoclinic crystal system , transmission electron microscopy , analytical chemistry (journal) , chemistry , crystal structure , nanotechnology , hexagonal crystal system , chromatography
Structural evolution during the phase transition from h (hexagonal)‐ to c (cubic)‐boron nitrides (BN) under high pressure (6.5–7.7 GPa) at high temperature (1,700–2,150°C) was examined by using high‐resolution transmission electron microscopy (HRTEM) and electron energy loss spectroscopy (EELS). At the initial stage of the evolution, some starting h‐BN plates were strongly folded, while others were slightly bent. As a result, a strong texture was formed. HRTEM revealed that the interplanar distance between sp 2 sheets became slightly shortened and they were slightly sheared to each other during the folding and bending. As a result, m (monoclinic)‐BN was formed near the folding plane with lattice parameters; a = 0.433 nm, b = 0.250 nm, c = 0.32–0.33 nm, and β = 90–92°. In a succeeding stage, the value of β increased to 92–95°. c‐BN grains appeared with nano‐scale twins and sometimes partly included wurtzite‐type BN. They started to grow with secondary twins at higher temperature. EELS analysis revealed that the band structure of sp 2 sheets changed during the transition from h‐BN to m‐BN; the density of state for the π bond became prominently high in m‐BN as compared to that in h‐BN. Microsc. Res. Tech. 40:243–250, 1998. © 1998 Wiley‐Liss, Inc.