Unravelling mechanisms for the formation of amorphous bands in B₆O under nonhydrostatic pressure

Boron suboxide (B6O) with superhardness holds great promise for a wide range of practical applications, but suffers from a low fracture toughness due to the formation of unusual nanoscale amorphous bands. Understanding of the underlying deformation mechanisms in this material, however, has been hindered limited experimental evidences. Here we report the discovery of new mechanisms for the formation of amorphous bands in B6O under nonhydrostatic pressure, based on in-situ high-pressure optical absorption measurements and analysis of postmortem samples. We find that the bandgap of B6O is sensitive to plastic deformation, offering an effective approach for exploring deformation behaviors of this material. Two new amorphous bands are identified along two distinct crystallographic planes of (1 (1) over bar0 (4) over bar) and (4 (3) over bar(1) over bar(8) over bar) associated with unbonded O-O pairs. Our findings establish a methodology for in-situ probe of plastic deformation in brittle materials, and demonstrate how their properties can be altered by plastic deformations under nonhydrostatic pressures. (C) 2021 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.