SPECIFIC-HEAT, THERMAL-EXPANSION, AND PRESSURE DEPENDENCIES OF THE TRANSITION-TEMPERATURES OF DOPED CUGEO3

We present high-resolution measurements of the specific heat and the t hermal expansion of the inorganic spin-Peierls cuprate CuGeO3 doped wi th 1.4% Zn and 0.5% Si, respectively. Both compounds exhibit rather we ll-defined spin-Peierls transitions at about 11 K, which cause anomali es in both the specific-heat and the thermal-expansion coefficients. B y comparing these anomalies we derive very large pressure dependencies of the transition temperatures. In particular, the pressure dependenc ies of the doped compounds are significantly larger than those in pure CuGeO3. From this difference we conclude that the suppression of the spin-Peierls transition in CuGeO3 by doping with Zn or Si is significa ntly reduced under pressure.