Pressure dependence of the electrical resistivity of natural cassiterite SnO2 and of undoped and Co-doped nanocrystalline SnO2

The pressure dependence of the electrical resistivity of three different samples of cassiterite, namely natural cassiterite SnO2, synthetic nanocrystalline SnO2 (with crystallite size 46 nm) and nanocrystalline Co-doped SnO2 (with crystallite size 32 nm), has been measured up to 7 GPa at room temperature. The resistivity of natural cassiterite SnO2 decreases from 2.5 x 104 m at normal pressure and temperature to 1.7 x 104 m at 7.0 GPa. The nanocrystalline SnO2 has a high resistivity 6.0 x 105 m at normal pressure and temperature and decreases with pressure reaching a value of 2.98 x 105 m at 7 GPa. The activation energy of the electrical conduction of the studied samples were found to be 0.32 eV for the natural SnO2, 0.40 eV for the nanocrystalline SnO2 sample and 0.28 eV for the nanocrystalline Co-doped SnO2. Measurements of the pressure dependence of the electrical resistivity of the Co-doped SnO2 showed a decrease from 3.60 x 105 to 5.4 x 104 m at 7.0 GPa. We did not observe any pressure-induced phase transition in SnO2 up to 7 GPa. This study of the high-pressure phase stability of cassiterite corroborates the experimental findings of SnO2 nanoinclusions in diamonds.