Effect of Li- and Ta-doping on the ferroelectric properties of Na0.5K0.5NbO3 thin films prepared by a chelate route

Abstract

The effects of lithium and tantalum doping on the properties of Na0.5K0.5NbO3 (NKN) thin films were investigated. The films were fabricated by an optimized chelate route which offers the advantage of a simple and rapid solution synthesis. The optimization was achieved by investigating the effects of alkaline volatilization loss on film properties. In this way, NKN thin films fabricated by this conventional method exhibited good ferroelectric properties (Pr ~ 8 μC/cm2, and Ec ~ 55 kV/cm for undoped films annealed at 650 °C). This route was then used to grow Li (5%) and Ta (10%) substituted thin films. Such structures allowed us to compare the effect of these dopant cations on phase formation, microstructure and ferroelectric properties. We show that both modifications produced a remarkable improvement of the ferroelectricity. While the undoped material exhibited large leakage components in films annealed at 600 °C, films modified with Li or Ta presented well saturated ferroelectric hysteresis loops. In general, the remnant polarizations of the Ta-doped films are greater than those of the Li-doped samples. However, this feature is reversed for films annealed at 600 °C due to abnormal grain growth and the presence of a non ferroelectric secondary phase in the Na0.5K0.5Ta0.1Nb0.9O3 composition.