NEW SUPERCONDUCTIVE COMPOUNDS OF THE K2NIF4 STRUCTURAL TYPE HAVING A HIGH TRANSITION TEMPERATURE, AND METHOD FOR FABRICATING SAME

摘要

The superconductive compounds are oxides of the general formula RE2-xAExTM.O4-y , wherein RE is a rare earth, AE is a member of the group of alkaline earths or a combination of at least two member of that group, and TM is a transition metal, and wherein x 0.3 and 0.1 /= y /=0,5. The method for making these compounds involves the steps of coprecipitating aqueous solutions of the respective nitrates of the constituents and adding the coprecipitate to oxalic acid, decomposing the precipitate and causing a solid-state reaction at a temperature between 500 and 1200 DEG C for between one and eight hours, forming pellets of the powdered product at high presure, sintering the pellets at a temperature between 500 and 1000 DEG C for between one half and three hours, and subjecting the pellets to an additional annealing treatment at a temperature between 500 and 1200 DEG C for between one half and five hours in a protected atmosphere permitting the adjustment of the oxygen content of the final product.