R. Lacroix

Preliminary results on a centre in CaF2 crystals

Abstract Axially symmetric EPR spectrum of O - ions in CaF 2 has been observed and the constants of the appropriate spin-Hamiltonian determined. Data show formation of loosely bound (OF) 2- molecule ion.

The Vk centre in SrCl2 crystals

Abstract The V k centre has been observed in SrCl 2 single crystals and the constants of the spin-Hamiltonian have been determined. In analogy to the V k centre in CaF 2 it shows resolved hfs with the nearest neighbours on the molecular axis.

EPR of a centre in Y3+ doped artificial CaF2 crystals

Abstract A centre has been observed in artificial CaF 2 single crystala related to the simultaneous presence of oxygen and yttrium impurity ions. EPR measurements gave the constants of the appropriate spin-Hamiltonian.

I. EPR of Mn2+ in the ferroelectric and paraelectric phases of natural (Mg-Cl) boracite

Abstract The EPR spectra of natural boracites1 (Mg3B7O13Cl : Mn2+) have been measured between 4 K and 800 K and, for an optically checked single domain, between 4 K and 293 K.

II. EPR of Mn2+ in the three ferroelectric phases of Zn-Ci boracite, a model for the monoclinic phase with bigger cell is proposed

Abstract Animportant question concerning the structure of trigonal boracites1–7 is whether the metal sites are all of type “1” or all of type “2,3” or a mixture of both (see Figure 1 of our paper I, this conference). Another important one concerns the structure of the monoclinic phase of boracites. In this case only the lattice parameters of the Fe-I composition have been determined.6

E.P.R. study of Mn2+ ions in a boracite

Abstract The E.P.R. spectrum of Mn2+ ions, substituted for Mg2+ ions and measured in the ferroelectric phase of the Mg3B7O13Cl boracite, is essentially characteristic of a very large crystal field.

Electronic structure, charge distribution and x-ray emission spectra of V3Si

Abstract Cluster calculations of the electronic structure and charge distribution in V 3 Si have been performed using two different molecular orbital methods: a semiempirical LCAO and the MS X α model. The results are compared with X-ray emission spectra and band structure calculations. An analysis of the calculated electronic distribution reveals a charge transfer from Si-atoms to V-atoms, the additional charge on a V-atom being 0.6 e (LCAO) and 0.4 e (MS X α method). The results are in good agreement with experiment, which indicates that the cluster approach is adequate for the description of charge distributions and spectra characteristics of the A-15 compounds.

Jahn-Teller effect in trigonal symmetry

The Jahn-Teller effect in trigonal symmetry is treated in the case where a pair of electronic levels, one singlet and one doublet, are linearly coupled to a vibrational doublet. Methods of calculation are given for the vibronic levels and for the matrix elements of electronic operators. A few numerical examples are presented and the theory is used to explain the uniaxial stress effect on Co3+ in corundum.

Comment on the local deformation in the corundum (α-Al2O3) and the uniaxial stress effect on the impurity energy levels

It is emphasised that the local deformation around the cation in Al2O3 is different from the crystal deformation. The influence of this on the effect of uniaxial stress on impurity energy levels is discussed.

EPR and buerger precession study of orthorhombic Mg-Cl:Mn2+ boracite

Abstract A single ferroelectric domain of Mg-Cl:Mn2+ boracite crystal (orthorhombic phase) allowed to correlate the three inequivalent EPR sites with the three crystallographic ones.