High pressure conductivity study of the alpha-quartz->rutile transformation in GeO2

The electrical conductivity of pure crystalline GeO2 has been measured as a function of pressure and temperature, up to 4.2 GPa and 1000 degrees C, through the alpha-quartz --> rutile transformation. At all pressures investigated, the conductivity shows little change with increasing temperature in the low temperature region (below similar to 400 degrees C) whereas there is a distinct increase in the temperature dependence in the high temperature region. The conductivity of the rutile phase, with Ge in 6-fold coordination (Ge-[6]), is similar to 10 orders of magnitude greater than the conductivity of the alpha-quartz phase, where Ge is in 4-fold coordination (([4]) Ge). These conductivity data on Ge-[4] and Ge-[6] structures may provide benchmarks for conductivity behaviour in four and six coordinated Ge in binary GeO2 systems. Our results are consistent with previously reported kinetic data which indicate that the simultaneous application of pressure and temperature greatly enhances the rate of transformation from alpha-quartz to rutile.