We studied correlation between the sizes of crystallite and resistance ZrO₂ at the pressures 22 - 50 GPa and temperatures 77 - 400 K. Nanocrystalline praseodymium doped zirconia powders were produced using a microwave driven hydrothermal process under pressures up to 8 GPa. Nanopowders of zirconia with Pr in solid solutions having Pr contents of 0.5 mol %. The bulk material sample of zirconia having Y₂O₃ contents of 5 mol %. Size of crystallites changed from 10 to 500 nm.
The dc resistance measurements were carried out in a diamond anvil cell rounded cone-plane type.
At a pressures of about 30-37 GPa the ZrO2 resistance decreases by 3-4 orders of magnitude. It’s found that the transition pressure of ZrO₂ depends on crystallite size.The smaller the crystals the smaller the transition pressure. The reduction of transition pressure was observed to 10 nm. However at 10 nm the transition pressure rises steeply.
It is possible to suspect, that the surface effects essentially change ZrO₂ conductivity mechanism at high pressures.
At the pressure of about 40-48 GPa anomalies in the pressure dependence of the resistance and of the parameters which depend on the concentration, mobility, and activation energy of the charge carriers are found. This permit to suppose the high-pressure induced phase transformation at 40-48 GPa.
Furthermore we obtain that the activation energy depends on the crystallite size. The smaller the crystals the higher activation energy.
We studied relaxation processes in ZrO₂ under the high pressures and the room temperature.The analysis of experimental data has shown that the time function of electric resistance most precisely described by exponential function. It can be seen, that relaxation times depend on pressure and crystallite size.