Study of the relaxor behavior in BaTi_(1-x)Hf_xO_3 (0.20 < = x < = 0.30) ceramics

摘要

The influence of Hf doping on the structure and dielectric properties of BaTiO_3 has been studied. For this purpose Ba(Ti_(1-x)Hf_x)O_3 ceramics were prepared through solid-state reaction route at close compositions, having x = 0.20, 0.22, 0.23 and 0.30. The study was aimed to locate the exact hafnium concentration for normal to relaxor crossover in these ceramics. X-ray diffraction followed by Rietveld refinement, reveals the formation of single phase with Pm3m cubic structure. Temperature and frequency dependence of real (epsilon') and imaginary (epsilon") parts of the dielectric permittivity have been studied in the temperature range of 90-350 K, at frequencies between 0.1 kHz and 100 kHz. The dielectric permittivity variations with temperature show deviation from Curie-Weiss behavior and strong frequency dispersion. The deviation from Curie-Weiss behavior, discontinuous jump along with the change in the slope of T_m vs Hf concentration plot, and the degree of relaxation (gamma) approaching approx 2, indicate a crossover from normal to relaxor ferroelectrics. Substitution of Hf~(4+) for Ti~(4+) in BaTiO_3 introduces structural disorder, causing perturbations like local electric and strain fields. These perturbations reduce the long-range polar order resulting in relaxor behavior.