Effects of cation-size disorder in(La0.67Ca0.15Sr0.18)1−x(Gd0.67Ba0.33)xCoO3perovskites

Abstract

Effects of the A-cation disorder on the structural, magnetic and transport properties of the $\mathrm{AB}{\mathrm{O}}_{3}$-type $({\mathrm{La}}_{0.67}{\mathrm{Ca}}_{0.15}{\mathrm{Sr}}_{0.18}{)}_{1\ensuremath{-}x}({\mathrm{Gd}}_{0.67}{\mathrm{Ba}}_{0.33}{)}_{x}{\mathrm{CoO}}_{3}$ $(x=0.0,$ 0.1, 0.2, 0.3, and 0.4) are studied. Based on x-ray diffraction, two crystallographic phases coexist in the compounds, and a progressive transition from rhombohedral structure to orthorhombic structure takes place with increasing x, with which the cation disorder increases. Two resistive transitions, a metal-to-metal and a metal-to-semiconductor, occur subsequently with decreasing temperature, with the upper resistive transition coinciding with a magnetic one. Both resistive transitions vary against x, with the upper one from \ensuremath{\sim}223 to \ensuremath{\sim}190 K and the lower one from \ensuremath{\sim}95 to \ensuremath{\sim}160 K corresponding to a change of x from 0.0--0.3. The presence of cation-size disorder drives the system from the cluster-glass state into the spin-glass state, accompanied by an enhancement of the semiconducting character of the compounds. The weak Jahn-Teller effects and the spin state transition could be responsible for the special cation disorder effects in the Co-based perovskites.