Preparation and properties of multi-effect potassium sodium niobate based transparent ferroelectric ceramics

Abstract

Traditional transparent materials, including glasses and polymers, are chemically unstable and mechanically weak. Single crystals of some inorganic materials are also optically transparent, which are more stable than glasses and polymers. The fabrication of crystals, however, is relatively slow. Fortunately, transparent ceramics emerge as a promising candidate. Transparent ferroelectric ceramic is a kind of transparent ceramic with electro-optic effect, which also has excellent characteristics of conventional ceramics with excellent mechanical properties, resistance to high temperature, resistance against corrosion, and high hardness. Lead based transparent ferroelectric ceramic dominates this field for many years due to its superior electro-optic effect. Owing to the high toxicity of lead oxide, however, its development is significantly hampered. Therefore, it is greatly urgent to develop the lead-free transparent ferroelectric ceramics with excellent properties to replace the traditional lead based ceramics. In this paper, (K<sub>0.5</sub>Na<sub>0.5</sub>)<sub>0.94–3<i>x</i></sub>Li<sub>0.06</sub>La<i><sub>x</sub></i>Nb<sub>0.95</sub>Ta<sub>0.05</sub>O<sub>3</sub> (KNLTN-La<sub><i>x</i></sub>; <i>x</i> = 0, 0.01, 0.015, 0.02) lead-free transparent ferroelectric materials are fabricated by the conventional solid state reaction method and ordinary sintering process. The dependence of microstructure, phase structure, optical transmittance and electrical properties of the ceramic on composition are systemically investigated. The transparent ferroelectric ceramic with relaxor-behavior is obtained at <i>x</i> = 0.02. The optical transmittance of the ceramic near infrared region is as high as 60%. Meanwhile, the electrical properties of the ceramic at <i>x</i> = 0.01 still maintains a relatively high level (<i>d</i><sub>33</sub> = 110 pC/N, <i>k</i><sub>p</sub> = 0.267). In addition, the Curie temperature for each of all the samples is higher than 400 ℃. These results suggest that this material might be a novel and promising lead-free material that could be used in a large variety of electro-optical devices.