Epitaxial stabilization of (110)-layered perovskites of the RE2Ti2O7 (RE=La, Nd, Sm, Gd) family

Thin films of RE 2Ti2O7 (RE =La, Nd, Sm, Gd) were deposited on single crystal SrTiO3 (110) substrates at 900 °C using pulsed laser deposition. X-ray diffraction (XRD) results showed sharp (00k ) peaks (in θ –2θ scans) with narrow rocking curves (ω -scan peak widths of 0.4–0.9°), indicating that all compositions adopted the (110)-layered perovskite structure. While this is the stable structure for RE =La and Nd, it is metastable for RE =Sm and Gd. The metastable compounds are formed directly through epitaxial stabilization at these high temperatures and are shown to be isostructural to monoclinic La2Ti2O7. The a , b , and c lattice parameters decreased monotonically with decreasing size of the RE cation, while the monoclinic angle remained fairly constant. The epitaxial relationship between the (110)-layered RE 2Ti2O7 films and the SrTiO3(110) substrate was found by XRD and transmission electron microscopy to be View the MathML source{001}〈010〉film||{110}〈11¯0〉SrTiO3. The single-phase, metastable, epitaxial, 100 nm thick films maintained the layered perovskite structure even after annealing at 900 °C for two hours in 200 Torr of oxygen.