CRYSTAL-FIELD INTERPRETATION OF THE TEMPERATURE-DEPENDENCE OF THE FE-57 MOSSBAUER QUADRUPOLE SPLITTING IN 2 ORTHOPYROXENES

The temperature dependences of the M2 and the M1 ferrous quadrupole sp littings in two orthopyroxenes have been studied. The valence contribu tions to the EFG were calculated from the Boltzmann averages of the ex pectation values of the EFG components over the corresponding D-5 leve ls, while the lattice contributions were obtained from lattice summati ons. The proper D-5 level schemes were each determined by diagonalizat ion of the full crystal-field Hamiltonian, for which the operator coef ficients were calculated so as to take into account the real C-1 symme try of the FeO610- clusters. The calculations were based on the lattic e and the charge data related to ferrosilite.