Giant domain wall response of highly twinned ferroelastic materials

Many ferroelastic crystals display at sufficiently low measurement frequencies a huge elastic softening below Tc which is caused by domain wall motion. Materials range from perovskites to iron based superconductors and shape memory materials. We present a model—based on Landau-Ginzburg theory including long range elastic interaction between needle shaped ferroelastic domains—to describe the observed superelastic softening. The theory predicts that the domain wall contribution to the elastic susceptibility is different for improper and proper ferroelastic materials. A test of the theory against experimental data on SrTiO3, KMnF3, LaAlO3, LaAlO3,La1-xNdxP5O14, and NH4HC2O4·12H2O yields excellent agreement.