Phase Composition of Samarium Niobate and Tantalate Thin Films Prepared by Sol-Gel Method

Samarium niobate SmNbO₄ (SNO) and tantalate SmTaO₄ (STO) thin films (~100 nm) were prepared by sol-gel/spin-coating process on alumina substrates with PZT interlayer and annealing at 1000°C. The precursors of films were synthesized using Nb or Ta tartrate complexes. The improvement of the crystallinity of monoclinic M′-SmTaO₄ phase via heating was observed through the coexistence of small amounts of tetragonal T-SmTa₇O₁₉ phase in STO precursor at 1000°C. The XRD results of SNO and STO films confirmed monoclinic M-SmNbO₄ and M′-SmTaO₄ phases, respectively, with traces of orthorhombic O-SmNbO₄ (in SNO). In STO film, the single monoclinic M′-SmTaO₄ phase was revealed. The surface morphology and topography of thin films were investigated by SEM and AFM analysis. STO film was smoother with roughness 3.2 nm in comparison with SNO (6.3 nm). In the microstructure of SNO film, small spherical (~50 nm) and larger cuboidal particles (~100 nm) of the SmNbO₄ phase were observed. In STO, compact clusters composed of fine spherical SmTaO₄ particles (~20-50 nm) were found. Effect of samarium can contribute to the formation different polymorphs of these films for the application to environmental electrolytic thin film devices.