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

In the present study, lead-free (1 - x) Bi-0.5(Na0.8K0.2)(0.5)TiO3-xBiMnO(3) (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) similar to 14 mu C cm(-2), effective piezoelectric coefficient d(33)* similar to 116 pm V-1 and dielectric constant epsilon(r) similar to 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.