THE THEORY OF FLUCTUATIONS AND TEXTURE EMBRYOS IN STRUCTURAL PHASE-TRANSITIONS MEDIATED BY STRAIN

Structural phase transitions are considered in which the effective ordering interaction J(R(ij)) arises from local stresses induced by the ordering in cell i and propagated elastically to a distant cell j. The generalized Landau free energy functional is set up and four applications made. Firstly the origin of metastable tweed microstructures is shown to lie in the dense medium of strong embryonic tweed-like microdomains existing as fluctuations at temperatures as high as 2T(c) and above. Secondly the tweed-like pattern originates from the very anisotropic interaction associated with domain walls, and four cases are distinguished. Thirdly it is shown that the Landau-Ginzburg theory of the width and shape of a domain wall can be carried over in some cases but not others. Fourthly the magnitude of critical fluctuations is considered together with corresponding corrections to the Landau theory of the phase transition in the four cases.