Study of structural, dielectric and ferroelectric properties of lead-free BaTiO3 - K0.5Na0.5NbO3 ceramics

Abstract

Due to the strict regulations on human health and environmental issues, lead-based Pb(Zr,Ti)O3 PZT ceramics are strongly prohibited. In consequence of this, intensified research on alternative lead-free ceramics like K0.5Na0.5NbO3 (KNN), BaTiO3 (BT), Bi0.5Na0.5TiO3 (BNT) etc. has been gaining eminence day by day. In this research, the effect of compositional variation of (1-x)BT-xKNN solid solution (x=0 to x=1.0) on microstructure as well as electrical and optical properties was observed. Conventional solid state route was practiced by varying the sintering temperature from 850-1200oC. Using a wide range of sintering temperature was beneficial in finding the optimum temperature of densification for each composition. EDX was done for quantitative analysis of the sintered samples. Embellished chemical inhomogeneity due to the volatilization of alkaline elements was perceived. SEM revealed the formation of liquid phase along with cuboidal grain in KNN rich compositions. However, in BT rich samples, presence of liquid phase was inconspicuous. XRD revealed the development of ferroelectric solid solution with minor second phases in the range of 25-30o. The synthesized Ba1-x(K0.5Na0.5)xTi1-xNbxO3 ceramics showed a commendable dielectric as well as ferroelectric property witnessed by impedance analyzer and ferroelectric loop tracer respectively. The loss tangent showed a decreasing trend with frequency. Presence of more than one hump in loss tangent curve for KNN rich samples indicates the involvement of different types of polarization relaxation mechanism. Dipoles are assumed to be failed to follow the direction of applied electric field at these particular relaxation frequencies. Nevertheless, stoichiometric imbalance caused severe deterioration in electrical property for certain compositions by reducing the resistivity of the specimen. The leakage current density was found in the range of 10-3~10-5 A/cm2. Diffused reflectance test revealed the chronological red shift of samples by the addition of dopants. The observed values of direct band gap was between 3.09~3.26 eV.