On the Symmetry of Deformable Crystals

摘要: This study was motivated by my recognition of some difficulties in the theory phase transitions. LANDAU* [1] proposed a transitions crystals, covering cases where crystal symmetry undergoes change. Briefly and roughly, it excludes possibility various types changes symmetry. Unfortunately for theory, excluded are observed. I do not know good reference describing known exceptions. The discussion which follows refers to cubic-tetragonal transitions, 'which observed superconductors. According conversations have had with experimentists, other exceptions It is impossible be fooled, distinction between second order weak first transition fine one. However one assesses this, we reason look at critical eye, remove its imperfections. In discussing such exception, ANDERSON • BLOUNT [3] claim show that "... usually involve change internal than mere strain ...". Said differently, thermoelasticity should replaced involving larger list variables constitutive equations. If suggested cure work, conclusions LANDAU, most probably decrease number excluded. Considering nature calculations involved, seems me less clear merely enlarging state will accomplish they prove will. Thus, think spots LANDAU theory. & mention, but discount another, matters continuity. focus on another. might well inadequate, given fair hearing. As far as know, accepted knowledgeable workers, replace LANDAU's. Again considering LANDAU'S reasoning, help if could attribute thermodynamic potentials more invariance commonly done. Common molecular theories predict rather unconventional