Gallium spinel

The absorption due to relaxation between the possible directions of the Jahn-Teller distortions was observed initially in experiments done on the crystals of aluminum oxide (corundum), yttrium aluminum garnet, yttrium iron garnet, and lithium gallium spinel doped with 2>d ions [10,11]. 

Now we will overview some experiments that reveal the specificities of the Jahn-Teller effect in diluted crystals. First of all, we will discuss a justification of their relaxation origin. We have mentioned before that the first experiments were done on the crystals of aluminum oxide (corundum), yttrium aluminum garnet, yttrium iron garnet, and lithium gallium spinel doped with a number of 3d ions [10,11]. The main result was the discovery of attenuation maximum which was considered to be observed at cot 1 and reconstruction of the relaxation time temperature dependence. In some experiments reported later both the velocity and attenuation of ultrasound were measured as functions of the temperature. They were done on ZnSe and ZnTe crystals doped with transition metals. These crystals have the zinc-blende structure with the Jahn-Teller ion in tetrahedral coordination. The following... 

Aluminum, gallium, and thallium form mixed oxides with other metals. First, there are aluminum oxides containing only traces of other metal ions. These include ruby (Cr3+) and blue sapphire (Fe2+, Fe3+, and Ti4+). Synthetic ruby, blue sapphire, and gem-quality corundum are now produced synthetically in large quantities. Second, there are mixed oxides containing macroscopic proportions of other elements, such as spinel (MgAl204) and crysoberyl (BeAl204). 

Principal experimental data on spinel-melt partitioning are those of Nielsen et al. (1994) for scandium, nickel, vanadium, zirconium, hafnium, niobium, tantalum, uranium, and thorium and Horn et al. (1994) for scandium, vanadium, gallium, zinc, cobalt, zirconium, hafnium, niobium, and tantalum. These are supplemented by data for hydrous melts by Nielsen and Beard (2000). 

McDonough W. F. (1990) Comment on Abundance and distribution of gallium in some spinel and garnet Iherzolites by D. B. McKay and R. H. Mitchell. Geochim. Cosmochim. Acm 54, 471-473. 

For reasons which will become clear later, we cannot use chromium-spinels or iron-spinels as a phosphor base. Thus, we are limited to aluminum, tin and the like. We will limit our discussion to tin and gallium-based compounds, i.e.- Mga SnO and Mg2Ga04. 

The analysis shows, as do diffraction methods, that gallium is coordinated tetrahedrally by oxygen. In addition, the Ga-O bond length of 1.83 A is obtained that cannot be determined directly from diffraction methods due to the partial occupation of the Ga sites by Si. As the negative value of Ad indicates, the deviations from the mean bond length are smaller in the sodalite than in the spinel compound. The parameter AEq bears no physical meaning,but o values which are larger than some eV point to false results. 

The theoretical search for new gallium oxonitride compounds was initiated following the observation of spinel-type structured materials that formed as side products... 

Figure 3.8 Monitoring the structural transformation with temperature and ammonia gas atmosphere starting from gallium nitrate reaching a spinel-type structured gallium...

Figure 3.11 In spinel-type structured gallium oxonitrides the lattice parameter Oq increases with higher nitrogen contents. The considered compositions are theoretically calculated regarding charge neutrality and considering a fllled-anion model.

Stone SF, Arean CO, Diez Vinuela IS, Platero EE (1985) Structural characterization of cadmium-copper gallium oxide (CdxCui.xGa204) spinels. J Chem Soc-Faraday Trans 81 1255-1261... 

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