Chemical pressure analysis of high temperature superconductors: Anisotropic effects in YBa2Cu3O7-x and YBa2(Cu1-yFey)3O7-x

Quantitative evaluation of selected sets of critical temperature and lattice parameter data for the orthorhombic compounds YBa2Cu3O7-x and YBa2(Cu1-y, Fey)3O7-x reveals a strongly anisotropic dependence of the critical temperature on these parameters, especially for YBa2Cu3O7-x. This method of deriving the relationship between critical temperature and changes in lattice constants is termed chemical pressure analysis (CPA). The signs of the anisotropic chemical pressure coefficients, ki, for the critical temperature of YBa2Cu3O7-x are found to be opposite to those determined for anisotropically applied physical (mechanical) pressure and of greatly increased magnitude. One explanation for these differences may be that physical pressures do not alter chemical bonds in the same manner as do chemical pressures. For pressures below 4 GPa, both CPA and physical pressure results indicate that increasing hydrostatic pressure increases Tc, but chemical pressures are found to be more effective at increasing critical temperature than are physical pressures. Hydrostatic pressures above 4 GPa, however, decrease Tc. Since the fracture strength of real crystals limits the magnitude of the anisotropic physical stresses that can be applied, only CPA appears capable of yielding the anisotropic dependence of critical temperature on individual lattice parameters in the ultrahigh stress regime above 4 GPa. © 1994.

Duke Scholars

Author F. Hadley Cocks Thomas Lord Department of Mechanical Engineering and Materia ...