Etching of diamond octahedrons at high temperatures and pressure with controlled oxygen partial pressure

Abstract

Etching of a natural diamond octahedron was carried out at temperatures of 800 to 1400° C and at pressures of 15 and 40 kbar under controlled oxygen partial pressure in the range 10−17 to 104 atm by use of oxygen buffers. Well-defined etch pits of equiangular triangule outline were formed. When the results were plotted based on log PO2 versus 1/T, reversal of the pit orientation clearly occurred on a boundary curve expressed by an equation, log PO2=−9.0×104/T+63, where PO2 (atm) and T (K) are oxygen partial pressure and temperature, respectively. Etch pits with the same orientation as an octahedral face were produced in a low temperature and high PO2 region, and those with the opposite orientation, i.e. the same as for natural “trigon”, were produced in the other region.