Superconducting and structural phase transitions in a pyrochlore oxide Cd2Re2O7 are studied under high pressure by x-ray diffraction and electrical resistivity measurements. A rich P-T phase diagram is obtained, which contains at least two phases with the ideal and slightly distorted pyrochlore structures. It is found that the transition between them is suppressed with increasing pressure and finally disappears at a critical pressure Pc = 3.5 GPa. Remarkable enhancements in the residual resistivity as well as the coefficient A of the AT 2 term in the resistivity are found around the critical pressure. Superconductivity is detected only for the phase with the structural distortion. It is suggested that the charge fluctuations of Re ions play a crucial role in determining the electronic properties of Cd2Re2O7.
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