Growth condition related orientation transition for YBa2Cu3O7−δ films on NdGaO3 substrate

► Orientation transition of YBa2Cu3O7−δ films was investigated by liquid phase epitaxy. ► Unpredicted c-oriented films formed at temperatures above the YBa2Cu3O7−δTp. ► A double transition of the c-axis→a/c mixed→c-axis film grown in air was unveiled. ► A single evolution of the c-axis→a-axis orientation phase was obtained in O2. ► A comprehensive mechanism of out-of-plane orientation control is presented.