Structure and T-c of Y0.8Ca0.2Ba2Cu3O6.92 under high pressure

The lattice parameters and T-c of Y1-yCayBa2Cu3Ox have been determined unde r pressure up to 10 GPa using a diamond anvil cell. The results are used to test the extended charge transfer model that connects the pressure effect on T-c to an intrinsic dT(c,max)/dp and a pressure induced hole doping dn(h )/dp, the latter being caused by charge transfer from the CuO chains to the CuO2 planes, dnh/dp and dT(c,max)/dp are usually assumed to be constant wi th respect to pressure p. However, our experiments show that the usage of t his model gives a poor description of the experimental T-c(p) values. We co nnected the extended charge transfer model to the pressure induced changes of the compressibilities. With this ansatz the calculated T-c(p) values sho w an excellent agreement with the experimentally determined values.