Effect of Mn doping on microstructure and electrical properties of the (Na0.85K0.15)0.5Bi0.5TiO 3 thin films prepared by sol-gel method

Abstract

x mol% Mn-doped (Na0.85K0.15)0.5Bi 0.5TiO3 (NKBT-Mnx, x=0, 2, 4, 6, 8, and 10) thin films were deposited on Pt(111)/Ti/SiO2/Si substrates via an aqueous sol-gel method. The effects of Mn contents on the microstructure and electrical properties of NKBT films are investigated in detail. X-ray diffraction indicates that B-site Mn substitutions do not change the perovskite structure. However, when Mn-doping concentration above 6 mol%, the impurity phase of Mn oxide exist. Raman spectra show that a new Raman mode at about 706 cm-1 appears with Mn doping. And the gradual enhancement of this new Raman mode with increasing Mn-doping concentration confirmed the Mn substitution for B-site Ti in NKBT thin films. The ferroelectric measurement of the films indicated that, with the increase of Mn-doping concentration, the remnant polarization P r values increased firstly with a maximum value at 6 mol% and then decreased. The optimal ferroelectric properties was obtained in the film with x=6, giving the remnant polarization (Pr) and coercive field (E c) values of the films of 19.2 μC/cm2 and 106 KV/cm, respectively. According to dielectric measure, it is noted that the NKBT film with 6 mol% Mn doping exhibits the best dielectric property with dielectric constant of 492 and dielectric loss of 0.051. Owing to the reduction of transition from Ti4+ to Ti3+ and reducing the number of intrinsic oxygen vacancies, the NKBT-Mn6 shows lower leakage current density than NKBT thin film. A typical "butterfly" shape displacement-voltage loop was observed for the film samples, and piezoelectric response shows similar trend to the dielectric response with the increase of Mn-doping concentration. © 2011 The American Ceramic Society.