A-site ordering and its effect on tilting transition in perovskite La0.75Sr0.25FeO3-δ investigated by mechanical spectroscopy

La0.75Sr0.25FeO3-delta polycrystalline samples were prepared by the solid state reaction at different sintering temperatures. An octahedral tilting Pnma <-> R (3) over barc transition in La0.75Sr0.25FeO3-delta was detected by mechanical spectroscopy, where a dip of reduced modulus was observed and accompanied by a sharp internal friction peak. The modulus softening is due to the strain/order parameters coupling at this improper ferroelastic transition. The tilting transition shifts toward lower temperature with reducing sintering temperature in La0.75Sr0.25FeO3-delta samples, which is due to the detriment of A-site ordering in the ABO(3) perovskite. A higher degree of A-site ordering favors more homogenous structural modulation, which stabilizes the low temperature Pnma phase and results in the shift of the transition to higher temperature. Another internal friction peak just below the tilting transition was observed, which is attributed to domain wall motions. A correlation between the mobility of ferroelastic domain walls in Pnma perovskite and the existence of the high temperature R (3) over barc phase was suggested. Published by AIP Publishing.