X-Ray Diffraction Measurement of the Effect of Layer Thickness on the Ferroelectric Transition in EpitaxialKTaO3/KNbO3Multilayers

${\mathrm{KTaO}}_3/{\mathrm{KNbO}}_3$ strained-layer superlattices of variable periodicity were grown by pulsed laser deposition on ${\mathrm{KTaO}}_3$ substrates. The ${\mathrm{KNbO}}_3$ layers were found to be strained in plane to match the substrate lattice parameter. Therefore, the applied strain is independent of the layer thickness. High-temperature x-ray diffraction was used to measure the ferroelectric-paraelectric phase transition temperature $T_c$. For superlattice periodicity $\Lambda \le 5.1\mathrm{nm}$, $T_c=475\mathrm{}\mathrm{K}$, independent of $\Lambda$. For $\Lambda >5.1\mathrm{}\mathrm{nm}$, $T_c$ increases to 825 K at $\Lambda =33.8\mathrm{}\mathrm{nm}$.