High-temperature relaxor ferroelectric behavior in Pr-doped $\mathrm{Sr}\mathrm{Ti}{\mathrm{O}}_3$

Temperature-dependent Raman scattering, dielectric, and powder x-ray diffraction studies have been carried out on Pr-doped $\mathrm{Sr}\mathrm{Ti}{\mathrm{O}}_3$ ceramic samples. Activation of $\mathrm{T}{\mathrm{O}}_2$ and $\mathrm{T}{\mathrm{O}}_4$ polar modes indicated increasing degree of polar distortion by Pr doping. Dielectric measurements revealed that the system exhibits dielectric relaxation peaks at $\sim 500\mathrm{K}$. The softening tendency of the polar $\mathrm{T}{\mathrm{O}}_1$ soft mode decreases with increasing Pr doping. X-ray diffraction results show no evidence of symmetry breaking across the dielectric peak temperatures. The system exhibits features of high-temperature relaxor ferroelectrics.

Figure 1

Raman spectra of ${\mathrm{Sr}}_{1-x}{\mathrm{Pr}}_x\mathrm{Ti}{\mathrm{O}}_3$ for $x=0.00$, 0.025, 0.05, and 0.075 at $300\mathrm{K}$. The inset in the lowest panel shows magnified plot in a limited frequency range. For convenience, the various modes are labeled in alphabetical order in the lowest panel (see text).

Figure 2

Raman spectra of ${\mathrm{Sr}}_{0.975}{\mathrm{Pr}}_{0.025}\mathrm{Ti}{\mathrm{O}}_3$ at various temperatures

Figure 3

Raman spectra of ${\mathrm{Sr}}_{0.925}{\mathrm{Pr}}_{0.075}\mathrm{Ti}{\mathrm{O}}_3$ at various temperatures

Figure 4

Magnified plot of $\mathrm{T}{\mathrm{O}}_1$ mode of (a) ${\mathrm{Sr}}_{0.95}{\mathrm{Pr}}_{0.05}\mathrm{Ti}{\mathrm{O}}_3$ and (b) ${\mathrm{Sr}}_{0.925}{\mathrm{Pr}}_{0.075}\mathrm{Ti}{\mathrm{O}}_3$ at three representative temperatures. The $\mathrm{T}{\mathrm{O}}_1$ mode retains its softening tendency in (a) while it is almost temperature independent in (b).

Figure 5

Temperature variation of frequency of the $\mathrm{T}{\mathrm{O}}_1$ mode of ${\mathrm{Sr}}_{0.975}{\mathrm{Pr}}_{0.025}\mathrm{Ti}{\mathrm{O}}_3$.

Figure 6

Variation of the difference of the frequency of the $\mathrm{T}{\mathrm{O}}_1$ mode at $298\mathrm{K}$ and $773\mathrm{K}$ with composition. The graph shows that Pr doping gradually decrease the softening ability of the $\mathrm{T}{\mathrm{O}}_1$ mode.

Figure 7

(Color online) Temperature variation of real (upper plots) and imaginary parts (lower plots) of the relative dielectric permittivity at various frequencies: (a) $0.4\mathrm{kHz}$, (b) $1\mathrm{kHz}$, (c) $4\mathrm{kHz}$ (d) $10\mathrm{kHz}$, (e) $40\mathrm{kHz}$, and (f) $100\mathrm{kHz}$. The arrows indicate the direction of increasing frequency. The inset shows magnified plot of the real and imaginary parts of relative permittivity at $40\mathrm{kHz}$.

Figure 8

Powder x-ray diffraction profiles of (a) {111}, (b) {200}, and (c) {220} cubic Bragg reflections of ${\mathrm{Sr}}_{0.95}{\mathrm{Pr}}_{0.05}\mathrm{Ti}{\mathrm{O}}_3$.