Phase transformation and dielectric characteristics in Ba0.85Ca0.15Ti1−x(Mg1/2W1/2)xO3 ceramics

• (Mg1/2W1/2)4+ substitution for Ti4+ ions results in the formation of a second phase of BaWO4 at x=0.05 and a structural change from a tetragonal phase to a cubic one.
• A gradual change from normal ferroelectric characteristics to typical relaxor behaviour is observed.
• The dielectric relaxation is modelled using the Vogel–Fulcher relationship with a dozen meV.
• The high activation energy for high substitution level may be ascribed to more defect pair [mgTi׳׳−V0׳׳].

Structure, phase transformation and dielectric properties of Ba0.85Ca0.15Ti1−x(Mg1/2W1/2)xO3 ceramics with 0.02≤x≤0.20 have been investigated by means of X-ray diffraction, Raman and dielectric spectroscopy. X-ray diffraction and Raman results show that (Mg1/2W1/2)4+ substitution for Ti4+ ions results in the formation of a second phase of BaWO4 at x  =0.05. Dielectric measurements reveal a gradual transformation from normal ferroelectric characteristics to typical relaxor behaviour. A more reasonable relationship f=f0exp[−p(Ea/kBTm)]f=f0exp[−(Ea/kBTm)p] is introduced to characterise the dielectric relaxation, which yields an activation energy with ~27 meV. The high activation energy for the composition with a high (Mg1/2W1/2)4+ level may be ascribed to more defect pair [mgTi׳׳−V0׳׳].