Resistivity measurement under pressure, X-ray study, DC Hall effect an
d optical measurement were carried out on (BEDT-TTF)4[Pt(C2O4)2] to in
vestigated the nature of two types of phase transitions, i.e. metal-me
tal(M-M) transition ( Tc=200K under ambient pressure) and metal-insula
tor (M-I) transition (Tc=60K, under ambient pressure). The M-M transit
ion temperature was found to increase on applying the pressure, while
the M-I transition was found to disappear above 4kbar. It is suggested
that the M-M transition is due to CDW formation.