Phase control of La₂CuO₄ in thin film synthesis

The lanthanum copper oxide, La2CuO4, which is an end member of the prototype high-T-c superconductors (La,Sr)(2)CuO4 and (La,Ba)(2)CuO4, crystallizes in the K2NiF4 structure in high-temperature bulk synthesis. The crystal chemistry, however, predicts that La2CuO4 is at the borderline of the K2NiF4 stability and that it can crystallize in the Nd2CuO4 structure at low synthesis temperatures. In this article we demonstrate that low-temperature thin-film synthesis actually crystallizes La2CuO4 in the Nd2CuO4 structure. We also show that the phase control of K2NiF4-type La2CuO4 versus Nd2CuO4-type La2CuO4 can be achieved by varying the synthesis temperature and using different substrates.