Microstructure and electric properties of (Na 0.85 K 0.15 ) 0.5 Bi 0.5 TiO 3 composited films with alternative TiO 2 layers

In this work, in order to investigate the effect of TiO 2 layer on the microstructure and piezoelectric properties of (Na 0.85 K 0.15 ) 0.5 Bi 0.5 TiO 3 ( NKBT ) thin films, TiO 2 layer was inserted at the interface between the NKBT thin film and substrate and on both sides of the NKBT , i.e., at the interface and on the top of the NKBT thin film. NKBT composited films with alternative TiO 2 layer were deposited on Pt/Ti/SiO 2 /Si substrate by aqueous sol‐gel method. X‐ray diffraction observation found that the degree of (100) preferred orientation strengthened with TiO 2 layers added, especially on both sides of NKBT thin film. The TiO 2 / NKBT /TiO 2 composited film with both TiO 2 layer of 40 nm thickness exhibited a remnant polarization value P r of 22.6 μc/cm 3 and effective piezoelectric coefficient d 33∗of approximate 77 pm/V, which are much larger than that of the single‐layered NKBT thin film with P r value of 13.7 μc/cm 3 and d 33∗of 56 pm/V, respectively. According to the investigation of the temperature‐dependent ferroelectric property, it was found that the P r gradually increased, and in the meantime the coercive voltage gradually moved to higher voltage with testing temperature varied from 20 to −150°C. Besides, applied voltage dependence of leakage current density measurement indicated that the TiO 2 layer would effectively lower the leakage current of the films, and the TiO 2 / NKBT /TiO 2 composited film both TiO 2 layer of 40 nm exhibited the lowest leakage current.