Investigation of lanthanum substitution in lead-free BNBT ceramics for transducer applications

The influence of lanthanum on structural, dielectric, hysteresis and electric-field-induced strain behavior in lead-free, Bismuth Sodium Barium Titanate (BNBT7) system Bi0.465−xLaxNa0.465Ba0.07TiO3 (x=0.00 to 0.10 in steps of 0.02) near the morphotrophic phase boundary has been investigated. X-ray diffraction confirms the single-phase perovskite structure with co-existence of rhombohedral and tetragonal phases has been observed in all densely packed materials. The diffuse phase transition is evident from the study of the temperature dependence of dielectric constant at different frequencies. All the samples have shown relaxor type behavior. The compositions BNBT7 and lanthanum substituted BNBT7 (x=0.02) have been considered to be suitable for transducer applications on the basis of measured parameters like dynamic piezoelectric constant d*33, 152 and 147 (pm/V), piezoelectric voltage constant g33, 14.36 and 13.37 (10−3 mV/N) and coercive field (Ec) is, 14.78 and 9.24 (kV/cm) respectively.