Effects of Ca doping on the Curie temperature, structural, dielectric, and elastic properties of Ba0.4Sr0.6-xCaxTiO3 (0≤x≤0.3) perovskites -: art. no. 084108

The effects of Ca doping on the Curie temperature, structural, dielectric, and elastic properties of Ba0.4Sr0.6-xCaxTiO3 (0 <= x <= 0.3) has been studied. Powder x-ray diffraction revealed that the cubic lattice constant a decreases linearly with increasing x from 0 to 0.15, while showing an anomalous expansion between x=0.15 and x=0.18. This, together with the anomalies in the dielectric constants, Curie temperature T-C, and elastic constants observed for 0.15 < x < 0.18, suggests that a small amount of Ca ions substituted for Ti ions. Correlated with the evolution of a with x, T-C increases linearly with increasing x from 0 to 0.15; while deviating from linear behavior for x > 0.15, T-C increases persistently up to x=0.25 and thereafter shows a decrease. These variations of T-C with x have been interpreted in terms of Ca-doping-induced A-site cation size variance, a substitution of a small amount of Ca ions for Ti ions, and structural phase separation. Upon cooling the longitudinal elastic constant C-L shows drastic softening near T-C, arising from the electrostrictive coupling between the polarization fluctuations and the elastic strains. Moreover, it was found that Ca doping induces the hardening of C-L just below T-C, and the magnitude of the relative hardening of C-L (i.e., Delta C-L/C-L) increases with increasing x, implying that the tetragonal ferroelectric phase was increasingly stabilized by Ca doping. (c) 2005 American Institute of Physics.