Ferroelectric transitions by Ca substitution in Pb0.7 Nd0.2 TiO3

Abstract

Ferroelectric Pb0.7 (1-y) Ca0.7y Nd0.2 TiO3 (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 Pb0.7 Nd0.2 TiO3, 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 (0.20y0.40), accompanied by a decrease in transition temperature (TC or Tmax) at a linear rate of ∼8.2 K/at. %. The compositions with y<0.10 demonstrated the Curie-Weiss behavior in dielectric behavior, while those compositions of 0.20y0.40 could well be fitted to the Uchino equation with the diffusivity, in agreement with a relaxor ferroelectric behavior. At y0.50, ε′ was much reduced and became less sensitive to temperature. Neither ε max ′ nor frequency dispersion was detected in PCNT-0.50 and -0.60 in the ε′ -T plot, down to 80 K. © 2008 American Institute of Physics.