Influence of Al substitution on physical properties of Pr_0.67Sr_0.33Mn_1−x Al _x O₃ manganites

Abstract

We have investigated the effect of Al doping on physical properties of ${\rm Pr}_{0.67}^{3+}{\rm Sr}_{0.33}^{2+}{\rm Mn}_{0.67-x}^{3+}{\rm Al}_{x}^{3+}{\rm Mn}_{0.33}^{4+}{\rm O}_{3}^{2-}$ manganites synthesized using the solid-state reaction method at high temperature. Rietveld refinement of XRD patterns revealed that all samples crystallize in an orthorhombic structure with Pnma space group. Magnetization measurements show that all samples exhibit a paramagnetic–ferromagnetic phase transition at the Curie temperature T _C which decreases from 282 to 240 K when increasing Al content from x = 0.025 to 0.1, respectively. Electrical properties of samples have been investigated using admittance spectroscopy technique in 10²–10⁶ Hz and 100–320 K, frequency and temperature ranges, respectively. All samples exhibit a metallic behavior below the metal–semiconductor transition temperature (T _M–Sc) and a semiconductor behavior above T _M–Sc. The total conductance curves for our samples are found to obey Jonscher power law (G(ω) = G _dc + Aω ⁿ). The activation energy (E _a) increases with increasing Al content from 34.44 meV for x = 0.025 to 43.18 meV for x = 0.1. From AC conductance study, we deduced the binding energy (W _m) at 100 K. Its values decrease with Al content increases.