Growth orientation-related enhancement of electrical properties in (Na0.85K0.15)0.5Bi0.5TiO3-based composite films

Abstract

TiO2-coated (Na0.85K0.15)0.5Bi0.5TiO3 (NKBT) composite films with thicknesses of 250 nm and 650 nm are synthesized on Pt(111)/Ti/SiO2/Si using an aqueous sol-gel method. X-ray diffraction (XRD) in ω-scan and ψ-scan modes is performed to study the crystal orientation of the films. The electrical properties of the TiO2-coated NKBT composite films are investigated over a temperature range from -150 °C to150 °C. Compared to films without the TiO2 layer, the TiO2-coated NKBT films exhibit enhanced electrical properties, higher temperature stability, and better endurance performance, which can be ascribed to the combined effects of the highly (100)-preferred orientation and improved degree of crystallization. The composite film in which TiO2 layers are attached on both sides of the 650 nm-thick NKBT film demonstrates the best ferroelectric performance with the highest remnant polarization (Pr) of 24.2(±1.2) μC/cm2 under 750 kV/cm, the best piezoelectric performance with the highest effective piezoelectric constant (d33*) of 82(±4) pm/V, and the best electric performance with the lowest leakage current density of 4.5 × 10−6(±0.4 × 10−6) A/cm2 at 20 V. Piezoresponse force microscopy (PFM) further confirms the enhanced ferroelectricity and domain switching of the TiO2-coated composite films on a microscopic scale. In addition, the Pr values of the films increase gradually as the temperature decreases from 150 °C to-150 °C, while the d33* values exhibit the opposite trend, which is mainly attributed to the suppressed mobility of thedomain walls at low temperatures.