In-plane orientation of C-axis oriented YBa2Cu3Ox films on MgO substrates

The appearance of 45 degrees grain boundaries in c-axis oriented YBa2Cu3Ox films grown by pulsed laser deposition on MgO (001) substrates is discussed . X-ray phi-scan (in-plane orientation) measurements have revealed that YBa 2Cu3Ox films grown at around 700 degrees C have Two types of grains with [1 00](MgO) (-) parallel to [100](YBCO) and [110](MgO) parallel to [100](YBCO) in-plane epitaxial relationships. A plausible growth model is proposed fro m the viewpoints of lattice matching and ionic adhesive energy. The ratio o f 0 degrees and 45 degrees grains is found to be a function of the substrat e temperature. By decreasing the substrate temperature, we obtained c-axis oriented YBa2Cu3Ox thin films with only a [100](MgO) parallel to [100](YBCO ) in-plane epitaxial relation. We have eliminated the 45 degrees grain boun daries which drastically increase the surface resistance of the YBa2Cu3Ox f ilms for microwave applications.