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

Thin films of RE2Ti2O7 (RE = La, Nd, Sm, Gd) were deposited on single crystal SrTiO3 (110) substrates at 900 degrees C using pulsed laser deposition. X-ray diffraction (XRD) results showed sharp (00k) peaks (in 0-20 scans) with narrow rocking curves (omega-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 RE2Ti2O7 films and the SrTiO3(110) Substrate was found by XRD and transmission electron microscopy to be {001} < 010 >(film)parallel to{110}< 1 (1) over bar0 >(SrTiO3). The single-phase, metastable, epitaxial, 100 nm thick films maintained the layered perovskite structure even after annealing at 900 degrees C for two hours in 200 Torr of oxygen. (C) 2009 Published by Elsevier Inc.