Effect of uniaxial stress on pressure-induced metal-insulator transition in PrFe4P12

We have carried out electrical resistivity measurements on PrFe4P12 under high pressure using some kinds of pressure-transmitting mediums in order to investigate the effect of uniaxial stress on a pressure-induced metal-insulator (M-I) transition. In the measurement under uniaxial stress, the M-I transition appears at a lower pressure than in the case of quasi-hydrostatic pressure, indicating that the uniaxial stress is favorable to the insulating phase. On the other hand, the M-I transition appears suddenly with finite M-I transition temperature between 2.55 and 2.66GPa in the measurement under hydrostatic pressure. This fact suggests that the transition from the antiferroquadrupolar metallic phase to the insulating phase is of first order