Phase transitions in La0.5Sr0.5FeO3−δ investigated by mechanical spectrum

The mechanical spectrum measurement was performed in ceramic La0.5Sr0.5FeO3−δ from liquid nitrogen temperature to room temperature at kilohertz frequencies. From temperature dependent reduced modulus, a kink (corresponding temperature labeled as TM) was observed which evidenced a phase transition by the mechanical spectrum at two flexural resonance frequencies. This elastic manifested phase transition is a charge disproportionation transition. Around 170 K, an internal friction peak (labeled as P1) was observed accompanied with a large modulus hardening with the decrease in temperature. Two mechanisms are proposed for P1 peak, one is elastic manifestation of magnetic freezing, and the other is the ordering or freezing of oxygen vacancies.