Simple model for lattice parameters and T_c of superconductors with the K₂NiF₄ structure

A simple "internal stress" approach, based on basal plane lattice parameter variation with alkaline earth substitution, is proposed for predicting the superconducting transition temperature Tc of Ca, Sr and Ba-doped La2CuO4 superconductors. Alkaline earth solutes on the La site directly cause volume changes and Poisson distortions, and indirectly cause Jahn-Teller distortions and contractions of the transition metal site. With an empirical correlation between lattice parameter and Tc, this analysis predicts the effect of hydrostatic pressure, rationalizes observed lattice parameters and suggests other solutes. © 1987.