Structural properties of gadolinium orthoniobate and orthotantalate thin films prepared by sol-gel method

Abstract

Gadolinium orthoniobate GdNbO4 (GNO) and orthotantalate GdTaO4 (GTO) thin films (∼100 nm) were prepared by sol-gel/spin-coating process on Al2O3 substrates with Pb(Zr0.52Ti0.48)O3 (PZT) interlayer and annealing at 1000 °C. The precursors of films were synthesized using Nb or Ta tartrate complexes. We also report for the first time the FTIR, Raman spectra and morphology of tartrate GNO and GTO precursors annealed at various temperatures. The different phase transformation was determined in GNO or GTO precursors from fluorite T′-structure via orthorhombic O-GdNbO4 or cubic C-GdTa7O19 to monoclinic M-GdNbO4 or M′-GdTaO4 during annealing at 800–1200 °C. XRD results of GNO or GTO films confirmed the coexistence of M-GdNbO4 or M′-GdTaO4 phase in addition to O-GdNbO4 (in GNO) or C-GdTa7O19 (in GTO) as main phase at 1000 °C. The surface morphology and topography of thin films were investigated by the SEM and AFM analysis. GNO film was smoother with roughness of 7.31 nm in comparison with GTO (3.53 nm). The results of this work can contribute to the formation different polymorphs of these films for the application to environmental electrolytic thin film devices.