We are concerned with the phase transition behaviour of the cooperative Jahn-Teller T-e system and the T-t system in a simple cubic lattice. High temperature series expansions are derived for the specific heat and the elastic constants. In the latter case the symmetry has to be broken by...

A cluster series is established for the cooperative Jahn-Teller-T-e and theT-t-systems in the simple cubic and square lattices. We calculate the phase transition temperature Tc, the specific heat and the “susceptibility” in zero order and in 2-site cluster approximation. Additionally in the...