Synthesis of metal hydrides and in situ resistance measurements in a high-pressure diamond anvil cell

We have constructed a diamond anvil cell and a cryogenic system for high-pressure experiments at temperatures down to 1.5 K. A new mechanism is used to apply the force, and the body of the cell contains a heat-exchanger for use with liquid helium or liquid nitrogen. With the press, a maximum force of 30 000 N can be applied to the diamonds. The force can be changed at any temperature from outside the cryostat. We describe a technique to load metal samples with hydrogen at high pressures and do in situ resistance measurements. With this technique, we have synthesized stoichiometric PdH and PdD at a pressure of ∼4 GPa. We also have measured the pressure dependence of their superconducting transition temperatures. For PdH we find T_c=8.8 K and ∂ ln T_c/∂P=-6.8×10^-2 GPa^-1, and for PdD we find T_c=11.05 K and ∂ ln T_c/∂P=-5.0×10^-2 GPa^-1.