In Situ Synchrotron High-Pressure X-ray Analysis for ZnO with Rocksalt Structure

Zinc oxide (ZnO) with a rocksalt crystal structure is attractive because of the bandgap which lies in the range of visible light absorption (1.2-2.6 eV). However, the rocksalt structure is not stable at ambient pressure and temperature according to an equilibrium phase diagram. Nevertheless, this study demonstrates, for the first time, that it is possible to realize a 100% fraction of the rocksalt structure at ambient pressure and temperature. ZnO powder is initially processed by severe plastic deformation under high pressure through a technique of high-pressure torsion (HPT). The HPT-processed ZnO is then examined using a high-pressure application system available at BL04B1 of SPring-8 and in situ X-ray diffraction (XRD) analysis is conducted under high pressures at elevated temperatures. It is shown that the initial presence of the rocksalt structure produced by the HPT process is effective to attain a 100% fraction of the rocksalt structure.