Vanadium Oxide Precipitates in Sapphire Formed by Ion Implantation

Abstract

Some vanadium oxides undergo phase transformations which give rise to attributable for large variations in optical and electronic properties. Since one can expect dynamic rearrangement of implanted species and a distorted lattice due to implantation, we investigated the precipitation process under ion implantation at high temperature. Sapphire samples were implanted with 300-keV V⁺ ions at temperatures from 470 to 1070 K in a transmission electron microscope interfaced with ion accelerators. Evolution of vanadium oxide precipitates was observed simultaneously. Damage evolution such as dislocation loops and voids were observed at fluences of the order of 10¹⁸-10¹⁹ and 10²⁰ ions/m², respectively. At implantation fluence of the order of 10²¹ ions/m², dot and plate contrast was observed in addition to radiation damage. Electron diffraction analysis reveals that hexagonal and monoclinic V₂O₃, tetragonal and monoclinic VO₂, and V₇O₁₃ precipitates were formed in the substrate depending on the surface normal of the substrate. Some of precipitates were thermally unstable phases. Crystallographic relationship between matrix and the precipitates was investigated as well as the swelling effect both in the substrate and in the precipitates. Temperature dependence reveals precipitation starts at temperature higher than 670 K.