AC susceptibility measurements on ceramic YBa2Cu3O7.ysuperconductor in the GPa region

Ceramic high-Tc superconductor has intra-grain superconducting transition at TC1 and the inter-grain one at TC2. We investigated the effects of pressure on the ceramic superconductor YBa2Cu3O7-y in the pressure region up to 5.3 GPa, through the AC susceptibility measurements using a miniature diamond anvil cell (mDAC). The TC1 increases against the initial pressure, whereas it turns to decrease at around 2.5 GPa. The TC2 also exhibits similar pressure dependence. The up-and-down change of TC1 has been already observed in the previous single crystal experiment, whereas that of Tc2 was observed through the present study for the first time. From the viewpoint of measurement technique, we also point out some problems on the high pressure AC susceptibility measurements using a SQUID magnetometer.