Jahn-Teller effects in orbital triplets. II. The theory of D(T₂) ions in trigonal symmetry

For pt. I, see ibid., vol.7, 309 (1974). The problem of a D(T 2 ) ion showing trigonal symmetry and interacting with E-type distortions in the surrounding lattice is discussed. Two models are proposed; the first supposes that the trigonal field may be represented by a purely electronic operator and a cubic lattice while the second model assumes a trigonal lattice. Transformation methods are used in the analysis and it is shown that the two models give slightly different results for the effective hamiltonian describing the trigonal field. Finally, the second-order Jahn-Teller contribution from the trigonal field taken twice is shown to account for the very small trigonal field found experimentally in the Fe 2+ ; Al 2 O 3 system.