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

摘要

TiO2-coated (Na0.85K0.15)(0.5)Bi0.5TiO3 (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 omega-scan and psi-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 degrees C to 150 degrees 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 (P-r) of 24.2( +/- 1.2) mu C/cm(2) under 750 kV/cm, the best piezoelectric performance with the highest effective piezoelectric constant (d(33)*) of 82( +/- 4) pm/V, and the best electric performance with the lowest leakage current density of 4.5 x 10(-6)( +/- 0.4 x 10(-6)) A/cm(2) 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 P-r values of the films increase gradually as the temperature decreases from 150 degrees C to-150 degrees C, while the d(33)* values exhibit the opposite trend, which is mainly attributed to the suppressed mobility of the domain walls at low temperatures.