Mechanical behaviour of ferroelastic lanthanum metal oxides LaMO3 (MÂ =Â Co, Al, Ga, Fe)

The mechanical behaviours of lanthanum metal oxides LaCoO3 (LCO), LaAlO3 (LAO), LaGaO3 (LGO), and LaFeO3 (LFO) were investigated under uniaxial compression. Ferroelastic domain structures were observed as striped patterns in LCO, LAO, and LGO, but not in LFO. Rhombohedral LCO displayed a higher critical stress and larger hysteresis in its stress-strain curve than rhombohedral LAO, which could be attributed to the larger rhombohedral angle of LCO than that of LAO. Orthorhombic LFO-B (sintered at 1673 K) exhibited a larger hysteresis and stronger back-switching behaviour than orthorhombic LGO possibly because of the larger orthorhombic strain of LFO-B, whereas LFO-R (sintered at 1473 K) showed elastic behaviour. Comparison revealed that the rhombohedral ferroelastic materials exhibit smaller stress range for domain switching, resulting in more distinct ferroelastic mechanical behaviour, than the orthorhombic ones. This was confirmed by comparing the mechanical properties of LGO below and above its orthorhombic-to-rhombohedral phase transition temperature.