ROLE OF ELASTIC INTERACTION IN THE DISORDERED-PYRITE TO ORDERED-PYRITE PHASE-TRANSITION IN SODIUM SUPEROXIDE

We analyze the effect of indirect orientation-dependent elastic coupling between molecules, recently studied by Michel and Naudts in NaCN and KCN, on the disordered-pyrite to ordered-pyrite phase transition in sodium superoxide (NaO2). We find that the inclusion of this indirect interaction does not affect our earlier results on the order-disorder transition obtained by including only the direct interaction between the O2- molecules. We also discuss the interplay between direct and indirect interaction in the structural phase transitions seen in other alkali superoxides. © 1979 The American Physical Society.