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 deg. 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 0.4-0.9o), 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||{110}<11-bar0>SrTiO3. The single-phase, metastable, epitaxial, 100 nm thick films maintained the layered perovskite structure even after annealing at 900 deg. C for two hours in 200 Torr of oxygen. - Graphical abstract: Epitaxial thin films of RE2Ti2O7 (RE=Gd, Sm, Nd, and La) were deposited on single crystal SrTiO3 (110) substrates using pulsed laser deposition (PLD). All compositions adopted the monoclinic (110)-layered perovskite structure, which is the stable phase for La2Ti2O7 and Nd2Ti2O7 but is metastable with respect to the pyrochlore phase for Sm2Ti2O7 and Gd2Ti2O7.