Giant domain wall response of highly twinned ferroelastic materials

Many ferroelastic crystals display at sufficiently low measurement frequencies a huge elastic softening below T-c 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 center dot 1/2H(2)O yields excellent agreement.