Ferroelastic effect in lanthanum orthoferrite

Orthorhombic LaFeO₃, with spontaneous lattice strain (b - a)/(b + a) = 2.38 × 10⁻⁴, is shown by X-ray methods to be ferroelastic. The highly twinned as-grown crystals are detwinned by applying a compressive stress of about 2 MNm⁻² along a combined a, b direction. The 010] direction in a single crystal is reproducibly transformable into the 100] direction under uniaxial stress. The resulting ferroelastic transformation is caused by atomic displacements of 0.23 Å for La, 0.48 Å for O_I and 0.79 A for O_II, the Fe atom remaining invariant at an inversion center. Coupling is expected between the ferroelasticity and the dominant antiferromagnetic spin orientation, but not with the weak ferromagnetism.