Onset of spontaneous electrostrictive strain below 520 K in Pr-doped ${\text{SrTiO}}_3$

${\text{Sr}}_{0.95}{\text{Pr}}_{0.05}{\text{TiO}}_3$ ceramic is shown to exhibit anomalous value of cubic lattice parameter at room temperature. A combination of temperature dependent dielectric and synchrotron x-ray powder-diffraction study has revealed that the anomalous lattice parameter has contribution from spontaneous electrostrictive strain that sets in below 520 K. In analogy with the lead-based classical relaxor ferroelectrics, it is suggested that Pr-doped ${\text{SrTiO}}_3$ is a new class of high-temperature lead-free relaxor ferroelectric system.

Figure 1

Rietveld plot of x-ray powder-diffraction patterns of ${\text{Sr}}_{0.95}{\text{Pr}}_{0.05}{\text{TiO}}_3$ after refinement with cubic perovskite structure. The inset shows a magnified view of a limited range of data. The arrow inside the inset indicates the position of the anticipated 3/2 1/2 1/2 superlattice reflection (see text).

Figure 2

Raman spectrum of ${\text{Sr}}_{0.95}{\text{Pr}}_{0.05}{\text{TiO}}_3$ at 300 K. The inset shows a magnified plot of a selected region.

Figure 3

Observed (open circles), calculated (continuous line through the circles), and difference (continuous line at the bottom of the figure) neutron powder-diffraction pattern of ${\text{Sr}}_{0.95}{\text{Pr}}_{0.05}{\text{TiO}}_3$ at 300 K. The vertical bars indicate the calculated Bragg-peak positions. The inset shows a magnified view of the region where (marked by arrow) the 3/2 1/2 1/2 superlattice reflection is likely to appear (see text).

Figure 4

Temperature variation of unit-cell volume of ${\text{Sr}}_{0.95}{\text{Pr}}_{0.05}{\text{TiO}}_3$. The inset shows temperature evolution of spontaneous electrostrictive strain (see text). The error bars are smaller than the size of the filled circles.

Figure 5

Temperature variation of relative permittivity of ${\text{Sr}}_{0.95}{\text{Pr}}_{0.05}{\text{TiO}}_3$ at 1 kHz. The inset shows Curie-Weiss fit to the data above $T_m$.