ISING MODEL FOR INTERSTITIAL ALLOYS AND SUPERCONDUCTING OXIDES

Abstract

The interstitial alloys MZx with Z= H, C, N, O etc. at octahedral or tetrahedral sites of the fcc or bcc M lattice are analysed for nearest and next-nearest neighbor Z-Z interactions. Many compounds have repulsive interactions close to the borderline of maximum separation, which is characterized by Pauling’s electrovalence rule. There are also borderlines for attractive interactions, e.g. cluster formation or segregation. The new superconducting oxides Ba 2 YCu 3 O x, La 2 CuO 4, Bi 2 Sr 2 Ca n−1 Cu n O 2n+4 can be viewed as bcc M= Ba, Cu, Bi etc. lattice with Z= O atoms at octahedral sites. The low T c compounds Nbo , NbC x, TiO x, TiN x, PdH x, etc. have Z= C, N, O, H atoms at octahedral sites of the fcc M= Nb, Ti, Pd lattice.