LARGE QUADRUPOLAR INTERACTIONS IN RARE-EARTH COMPOUNDS

Several series of rare-earth compounds have been found to undergo structural phase transitions. For most of them the cause has been the cooperative Jahn-Teller effect. Here we point out that for TmZn and TmCd these transitions are not due to the cooperative Jahn-Teller effect. Rather they are driven by quadrupolar pair interactions. In these systems the lattice follows the quadrupoles and distorts in such a way as to minimize the Jahn-Teller coupling energy. © 1979 The American Physical Society.