CHEMICAL AND STRUCTURAL ASPECTS OF HIGH-TEMPERATURE SUPERCONDUCTORS

The chemical composition and crystal structures of high temperature superconducting (HTS) materials are reviewed. All of these materials can be described as a combination of conducting slabs and insulating slabs, and the discussion is based on the following observations. First, the crystal structure must allow the charge carriers to occupy those energy bands which are favourable to superconductivity. Second, the charge on the ions in the conducting slabs must be optimized. Third, the lattice parameters of the conducting and insulating slabs must match as closely as possible. All of these quantities can be varied by changing the composition of the layers within the conducting and insulating slabs; the aim of the solid-state chemist is to predict and then determine the composition which gives the maximum superconducting transition temperature for any particular HTS material.