The effect of low quasi-hydrostatic pressure on the melting temperature of the superconductor Bi2Sr2CaCu2O8+x

The effect of low quasi-hydrostatic pressure within the range 0-35 MPa on the melting onset temperature (Tm) of Bi2212 ceramics and composition of phases formed during melting were studied. There are two portions on the curve T n,(P) distinguished by a value of melting slope dTm/dP. Within the range 0-0.64 MPa an abnormally high value of dTm/dP about 92.19 deg C/MPa is observed, and the melting temperature increases from 875 deg C to 934 deg C. Above 0.64 MPa, the value dTm/dP, being much less, is about 0.08 deg C/MPa and the melting temperature increases up to 941 deg C. The pressure essentially influences the composition of Bi-free phase formed during melting of Bi2212: without pressure the (Sr,Ca)CuO, phase is formed, while under pressure higher than 0.64 MPa only the (Sr,Ca)14Cu24O41 phase is revealed. The effect of sharp increase in the melting temperature within the pressure range less than 0.64 MPa is explained by the fact that quasi-hydrostatic pressure preventing outflow of extra oxygen from the sample retards position disordering of the crystal lattice and thus increases its thermal stability.