Structural and electrical characterization of barium strontium titanate films prepared by sol-gel technique on brass (CuZn) substrate

The crystal structure, surface morphology and electrical properties of polycrystalline (Ba,Sr)TiO3 films were investigated. The barium strontium titanate (BST) films were prepared by sol-gel processing using barium acetate (Ba(CH3COO)(2)), strontium acetate (Sr(CH3COO)(2)) and titanium isopropoxide (Ti(OC3H7)(4)) as starting materials. Acetic acid and acetylacetone were selected as solvents. Six different types of gels were prepared, increasing the Sr2+ content from 0% to 50%. The films were deposited on brass (CuZn) substrate and then sintered at 750 degrees C for 2 h and annealed at 500 C for 1h. The single layer thickness of the films was about 10 pm. The surface morphology of the film was observed using a scanning electron microscope (SEM). X-ray diffraction (XRD) results show that the film exhibits a pure perovskite phase. The temperature dependence of resistance of films has been investigated and the results showed that the room-temperature resistivity decreases by increasing the Sr2+ content. In all cases the films showed a large negative temperature coefficient of resistivity, apart from the ferroelectric transition temperature where a PTCR peak response also appears. Such large temperature coefficient is attributed to the zinc and copper oxides, formed on the CuZn substrate due to its oxidation at elevated temperature, thus offering a significant temperature dependence effect for possible use in sensing applications.