Influence of tantalum on mechanical, ferroelectric and dielectric properties of Bi-excess Bi _3.25 La _0.75 Ti ₃ O ₁₂ thin film

The Bi-excess Bi _3.25 La _0.75 Ti ₃ O ₁₂ (BLT) and Bi _3.25 La _0.75 Ti _2.91 Ta _0.09 O ₁₂ (BLTT) thin films were deposited on Pt(1 1 1)/Ti/SiO ₂ /Si substrates using rf-magnetron sputtering method. The effect of tantalum on mechanical, ferroelectric and dielectric properties of BLT thin films was investigated. XRD patterns reveal that BLT and BLTT thin films have a same second crystalline phase Bi ₁₂ TiO ₂₀ , but the former has a randomly oriented major Bi ₄ Ti ₃ O ₁₂ phase while the major phase in the later is preferentially oriented along 〈1 1 7〉 direction. XPS analysis shows that the substitution of Ta ⁵⁺ has a significant influence on Ti ³⁺ defects. Mechanical response of thin films is discussed in the light of nano indentation analysis which shows that both the hardness and modulus are reduced with the addition of Ta ⁵⁺ . Ferroelectric properties were improved significantly by Ta ⁵⁺ doping due to the reduction of Ti ³⁺ defects, and an enhanced remnant polarization (2P _r ) of 32.5 μC/cm ² and a decreased coercive field (2E _c ) of 260 kV/cm were obtained. In addition, the Ta substitution elevated the dielectric constant and slightly raised the Curie temperature.