COMPETING INTERACTIONS AND ORIENTATIONAL ORDERING IN (NACN)1-X(KCN)X QUADRUPOLAR GLASSES

Molecular-dynamics calculations have been used to investigate the transition to an orientational-glass state in (NaCN)1-x(KCN)x mixtures. A previously unsuspected feature of the anion ordering was found. Whereas Na+ ions act as nucleation centers which cause neighboring CN- to lock into (100) orientations, other CN-, which do not have a Na+ nearest neighbor, strive to freeze into (111) pockets, but at a lower temperature. The competition between these two tendencies leads to an anomalous temperature dependence of the orientational oder parameters at low Na+ concentration.