Ferroelectric Transitions By Ca Substitution In Pb0.7nd0.2tio3

Ferroelectric Pb0.7(1-y)Ca0.7yNd0.2TiO3 (PCNT-y) compositions with y ranging from 0 to 0.60, were synthesized via a mechanical activation route. The tetragonality (c/a) of PCNT-y at room temperature decreases from 1.0125 to 1.0000 upon substitution of Pb2+ with smaller sized Ca2+. The composition with Ca-doping y=0.60 demonstrates a unit-cell volume shrinkage of 4.063% as compared to that of Pb0.7Nd0.2TiO3, while the Raman spectra are of the characteristic features of PbTiO3. As the Ca content (y) increases from 0 to 0.60, there is a crossover from a displacive phase transition (y=0 and 0.10) to a diffusive one (0.20 <= y <= 0.40), accompanied by a decrease in transition temperature (T-C or T-max) at a linear rate of similar to 8.2 K/at. %. The compositions with y < 0.10 demonstrated the Curie-Weiss behavior in dielectric behavior, while those compositions of 0.20 <= y <= 0.40 could well be fitted to the Uchino equation with the diffusivity, in agreement with a relaxor ferroelectric behavior. At y >= 0.50, epsilon' was much reduced and became less sensitive to temperature. Neither epsilon(max)' nor frequency dispersion was detected in PCNT-0.50 and -0.60 in the epsilon'-T plot, down to 80 K. (C) 2008 American Institute of Physics.