Charge order suppression in oxygen nonstoichiometric La1/3Sr2/3FeO3−δ

• Charge ordering is suppressed in oxygen nonstoichiometric La1/3Sr2/3FeO3−δ.
• A relaxation peak appears in mechanical spectrum and dielectric spectrum.
• Jahn–Teller effect in oxygen nonstoichiometric La1/3Sr2/3FeO3−δ stabilizes Fe4+.
• Jahn–Teller effect in La1/3Sr2/3FeO3−δ suppresses charge ordering.

Oxygen nonstoichiometric La1/3Sr2/3FeO3−δ sample was prepared and investigated by kilohertz mechanical spectroscopy and dielectric spectroscopy from liquid nitrogen to room temperature. Charge order is suppressed in oxygen nonstoichiometric La1/3Sr2/3FeO3−δ sample. Young's modulus shows conventional hardening with the decrease in temperature. It is different to previous observed lattice softening above charge ordering transition in as-prepared La1/3Sr2/3FeO3−δ sample. A relaxation process is observed in dielectric loss in oxygen nonstoichiometric La1/3Sr2/3FeO3−δ sample with the activation energy of 0.26 eV. It can be explained by electron hopping between Fe3+ and Jahn–Teller distorted Fe4+ ions. An internal friction peak around 130 K is explained similarly by stress induced electron hopping between Fe3+ and Fe4+. This work suggests that Fe4+ is stabilized by the Jahn–Teller distortion in oxygen nonstoichiometric La1/3Sr2/3FeO3−δ ceramic. This is expected to be the reason of charge order suppression in oxygen nonstoichiometric La1/3Sr2/3FeO3−δ sample.