Composition dependence of phase structure and electrical properties of BiMnO3-modified Bi0.5(Na0.8K0.2)0.5TiO3 thin films

Abstract

In the present study, lead-free (1 − x)Bi_0.5(Na_0.8K_0.2)_0.5TiO₃-xBiMnO₃ (abbreviated as BNKT-xBMO, with x ranging from 0 to 0.025) thin films were deposited on Pt/Ti/SiO₂/Si substrates by a sol–gel method, and the effects of BiMnO₃ addition on the crystal structure and electrical properties were systematically investigated. The results show that with increasing BiMnO₃ content the crystal structure undergoes a phase transition from a ferroelectric rhombohedral phase to rhombohedral-tetragonal coexisting phases to a relaxor pseudocubic phase. The superior ferroelectric, piezoelectric and dielectric properties were attained at x = 0.01 with remanent polarization 2P_r ∼ 14 μC cm⁻², effective piezoelectric coefficient d^*₃₃ ∼ 116 pm V⁻¹ and dielectric constant ε_r ∼ 270. The composition-dependent phase structure and optimal electrical properties indicated that the MPB-like behavior existed at around x = 0.01. Moreover, our study revealed that the end-member BiMnO₃ modified BNKT thin films provided a lead-free alternative in ferroelectric random access memory (FRAM) and piezoelectric actuator application.