Epitaxial perovskite KTaO3 films were grown hydrothermally on (100) oriented single-crystal SrTiO3 substrates in a 7 M KOH solution at 170 degrees C. Transmission electron microscopy, Rutherford backscattering spectroscopy, and optical measurements showed that despite the low growth temperature, the obtained films were highly crystalline. Also, determination of the residual strain due to grain coalescence, lattice mismatch, and thermal expansion mismatch indicated that differential contraction between the substrate and film during cooling generated sufficient compressive stress to cause film buckling at poorly bonded regions between the film and substrate. (c) 2007 The Electrochemical Society.