Effect of Sc Doping on the Structure and Electrical Properties of (Na0.85K0.15)0.5Bi0.5TiO3 Thin Films Prepared by Sol-Gel Processing

(Na0.85K0.15)(0.5)Bi0.5TiO3 (NKBT) and B-site-substituted NKBT by Sc, i.e. (Na0.85K0.15)(0.5)Bi0.5Ti(1-x)ScxO3 (NKBT-Scx, x = 0.05, 0.1, 0.15, 0.2, 0.25, 0.3, and 0.4) thin films were prepared on Pt/Ti/SiO2/Si(100) substrates by an aqueous sol-gel method. Structures and electrical characteristics of the films were studied as functions of Sc composition. Structures were investigated by X-ray diffraction (XRD), scanning probe microscopy, scanning electron microscopy, and Raman spectroscopy. XRD indicates that a secondary phase peak appears when Sc-doping concentration increases above x = 0.25 due to the limited substitution tolerance of Sc3+ for Ti4+. With increasing Sc-doping composition, generally, the octahedra-related vibration modes show a high-frequency shift. The remnant polarization (P-r) value is a maximum for the NKBT-Sc0.25 films of 18.62 mu C/cm(2) and decreases with both decreasing and increasing doping concentration. The NKBT-Sc thin film with an optimized Sc-doping concentration of x = 0.25 shows the effective piezoelectric coefficient d*(33) of 67 pm/V. The Curie temperature (T-c) of the NKBT thin film shifted to higher temperature by adding Sc dopant.