Effect of oxygen content on transport and magnetic properties of PrBaCo2O5.50+δ

Samples of PrBaCo2O5.50+δ (δ = −0.15–0.14), synthesized by solid-state reactions, were investigated to ascertain oxygen compositional effects on transport/magnetic properties. Resistivity decreases with increasing oxygen content, indicative of p-type conduction. A metal-insulator transition was observed at 330 K only for sample PrBaCo2O5.52, coinciding with phase transition and spin-state transition of Co3+. When δ deviates from zero, samples show insulator–insulator transitions, although for sample δ = 0.14, no transition occurs but only semi-conductive behavior appears. Electronic transport is governed by the hopping mechanism at lower temperatures and thermal activation at higher temperatures. All samples underwent paramagnetic–ferromagnetic–antiferromagnetic transitions, except PrBaCo2O5.64, which only went through a paramagnetic–ferromagnetic transition. The ferromagnetic state for δ < 0 originates with the Co3+/Co2+ super-exchange interaction; for δ > 0, it stems from the Co3+/Co4+ double exchange interaction.