Tetragonal sites

The charge compensation is provided by a Ca2+ vacancy which serves to compensate two Eu2+ ions. There are different arrangements for the Eu3+ and the Ca2+ vacancy as illustrated in the figure. The cubic site has the Ca2+ vacancy compensation so distant that the local symmetry of the Eu2+ is not perturbed. The tetragonal site has the vacancy in the nearest neighbor position. The dimer sites have the vacancy in the nearest neighbor positions for two symmetrically located Eu2+ ions. Each of these different Eu2+ sites has different crystal field splittings and spectra. 

Induced shifts of ligand atoms adjacent to rare earth ions are usually attributed to the contact interaction whereas shifts of more remote ligand atoms are generally considered to arise from a dipolar term. McGarvey (378,379) has described a reformulated covalent model which can account for the observed F hyperfine interactions for Yb and Tm " in cubic and tetragonal sites of alkaline earth... 

For the T u irrep, we can use the set of the p-orbitals. In the standard Cartesian orientation, this set is adapted to the tetragonal site symmetry. In Fig. 4.9 we illustrate an alternative trigonal basis (see also Fig. 3.6(d)). The transformation between the two sets is given by... 

Pre-exponential factors in the thulium nuclear relaxation rates, correlation times Tc of the h erfine field fluctuations, homogeneous r = h t and inhomogeneous F) half-widths of the Tm ion transitions from the ground singlet to the nearest doublet state (r4-F5) at the tetragonal sites in TmBa2Cu30ttx crystals (x-0-0.4)... 

R. V.S.S.N. Ravikumar, V. Rajagopal Reddy, A.V. Chandrasekhar, B.J. Reddy, Y.P. Reddy, P.S. Rao, Tetragonal site of transition metal ions doped sodium phosphate glasses. 1. Alloys Compd. 337(1-2), 272-276 (2002)... 

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