THE CRYSTAL-STRUCTURE OF RESRGACUO5 (RE-LA, PR, ND), A GALLATE CUPRATE WITH STRONG STRUCTURAL SIMILARITIES TO SUPERCONDUCTING CUPRATES

The crystal structure and some basic properties of RESrGaCuO5(RE:La, Pr, Nd, space group Ima2, z = 4, a = 16.277(1)Å, b = 5.5191(3)Å, c = 5.3342(3)Å for RE =Nd) has been studied by powder and single-crystal X-ray methods, electrical resistivity and magnetic susceptibility measurements, DSC, TG, and optical microscopy. The structure consists of almost planar nets of distorted cornersharing Cu{single bond}O6 octahedra connected along the longest axis via Ga{single bond}O4 tetrahedral chains with RE and Sr ions filling the large voids between planes and chains. It is isotypic to the structure of the mineral Brownmillerite (Ca2(Al,Fe)2O5). Together with its recently described double Cu{single bond}On layer counterpart RESR2GaCu2O7 it forms a homologous series of new gallate-cuprates which closely resemble the corresponding Ga-free superconducting cuprates with single and double Cu{single bond}On layers. Stoichiometric RESrGaCuO5 has a fixed oxygen content and is semiconducting with a strong anisotropy of the optical absorption, indicating a pronounced 2-dimensional character of the electronic properties. P-doping of these materials by partial substitution of RE by additional Sr has not been successful up to now. © 1992 Academic Press, Inc.