Hydrothermal epitaxy of KtaO₃ thin films

Heteroepitaxial KTaO₃ thin films were synthesized by the hydrothermal method below 175 °C in highly alkaline aqueous KOH solutions. KTaO₃ films synthesized in 7 M KOH solutions contained a defect pyrochlore phase that had (400) and (111) out-of-plane orientations. The (400) oriented pyrochlore islands were epitaxially related to the (100) SrTiO₃ substrate while the (111) oriented pyrochlore islands had four in-plane variants. Pyrochlore-free KTaO₃ films could be synthesized in a 15 M KOH solution. Pyrochlore-free films were also grown at 7 M KOH by delaying the introduction of the (100) SrTiO₃ substrate into the synthesis solution until the conditions favoring the formation of the pyrochlore phase had dissipated.