Fabrication of M³⁺-substituted and M³⁺/V ⁵⁺-cosubstituted bismuth titanate thin films [M = lanthanoid] by chemical solution deposition technique

Lanthanoid (M³⁺ = La³⁺, Pr³⁺", Nd³⁺ and Sm³⁺)-consubstituted and lanthanoid/vanadium (V⁵⁺)-cosubstituted bismuth titanate thin films were fabricated on (111)Pt/Ti/SiO₂/(100)Si substrates by a chemical solution deposition (CSD) technique. All the films consisted of a polycrystalline structure with random crystal orientation. Pe³⁺, Nd³⁺ and Sm ³⁺-substituted BIT films [BPT, BNT and BST] had larger remanent polarization (Pr) values than that of conventional La³⁺-substituted BIT film [BLT]; furthermore, the P_r value of the BNT film was higher than those of the BPT and BST films. On the other hand, no significant difference in the coercive field (E_c) value was found among those films. P_r and E_c values of the BNT film with y = 0.50 in (Bi_4.00-y, Nd_y.)Ti_3.00O₁₂ were measured to be 32 μC/cm² and 126kV/cm, respectively. V ⁵⁺-substitution varied the P_r value of the lanthanoid-substituted BIT films without changing the in E_c value. The Pr value of the BNT film with y = 0.50 was improved up to 37 μC/cm ² by V⁵⁺-substitution of x = 0.02 in (Bi_4.00-y, Nd_y) _1-(x/12) (Ti_3.00-x, V_x)O ₁₂ [BNTV]. Ferroelectric properties of the Pb-free polycrystalline BNT and BNTV films are comparable to those of conventional Pb-based ferroelectric films such as lead zirconate titanate [PZT] films.