Phase relations in the systems AO-X2O3(A:Ca,Sr,Ba;X:AI,Ga)

The double oxides of the systems AO-X2 O3 (A:Ca, Sr, Ba; X:Al, Ga) occur in several technologically important processes. Classical applications range from sulphate resistant cements to refractories. Recently, Ca-, Sr- and Ba- aluminates of various compositions have been intensively studied for the production of a new generation of persistent luminescence compounds. After doping with Eu2+ the aluminate phosphors show a broad band blue/green emission characteristic. The lifetime of the luminescence is far beyond the values of ZnS-based phosphors, the material used so far. Despite their technological relevance, the AO-X2 O3 phase diagrams contain many uncertainties concerning the melting points, the melting behaviour of the compounds and the number of existing phases. Therefore, one research direction of the current proposal entitled "Structural investigations and crystal chemistry of phases in the systems AO - X2 O3 (A: Ca, Sr, Ba ; X: Al, Ga)" will concentrate on a more detailed study of the phase relationships at ambient pressure in selected areas of the corresponding phase diagrams. The primary analytical technique will be X-ray structure determination from powder data collected on a high-resolution diffractometer. Further investigations will include solid state NMR, electron microscopy as well as measurements of the oxygen conductivity at elevated temperatures using impedance spectroscopy. Secondly, the project will focus on high pressure synthesis experiments up to 15 GPa in the alkaline earth aluminate and gallate systems. Preliminary studies have shown that high pressure can be used to stabilize new classes of quenchable materials with an unusual variety of coordination environments for the trivalent cations. Comparative studies of the corresponding Al- and Ga-compounds will allow for analyzing the influence of the cation size on the stability of different structure types. A third direction of the proposal will include in-situ high temperature diffraction studies. From the literature it is known, that several tetrahedral framework- and cyclo-aluminates/gallates undergo structural phase transitions between room temperature and 1000C. The previously unknown HT-modifications will be structurally characterized. In summary one can say, that the proposal will make a significant contribution to our knowledge of the crystal chemistry of main group elements.

The double oxides of the systems AO-X2 O3 (A:Ca, Sr, Ba; X:Al, Ga) occur in several technologically important processes. Classical applications range from sulphate resistant cements to refractories. Recently, Ca-, Sr- and Ba- aluminates of various compositions have been intensively studied for the production of a new generation of persistent luminescence compounds. After doping with Eu2+ the aluminate phosphors show a broad band blue/green emission characteristic. The lifetime of the luminescence is far beyond the values of ZnS-based phosphors, the material used so far. Despite their technological relevance, the AO-X2 O3 phase diagrams contain many uncertainties concerning the melting points, the melting behaviour of the compounds and the number of existing phases. Therefore, one research direction of the current proposal entitled "Structural investigations and crystal chemistry of phases in the systems AO - X2 O3 (A: Ca, Sr, Ba ; X: Al, Ga)" will concentrate on a more detailed study of the phase relationships at ambient pressure in selected areas of the corresponding phase diagrams. The primary analytical technique will be X-ray structure determination from powder data collected on a high-resolution diffractometer. Further investigations will include solid state NMR, electron microscopy as well as measurements of the oxygen conductivity at elevated temperatures using impedance spectroscopy. Secondly, the project will focus on high pressure synthesis experiments up to 15 GPa in the alkaline earth aluminate and gallate systems. Preliminary studies have shown that high pressure can be used to stabilize new classes of quenchable materials with an unusual variety of coordination environments for the trivalent cations. Comparative studies of the corresponding Al- and Ga-compounds will allow for analyzing the influence of the cation size on the stability of different structure types. A third direction of the proposal will include in-situ high temperature diffraction studies. From the literature it is known, that several tetrahedral framework- and cyclo- aluminates/gallates undergo structural phase transitions between room temperature and 1000C. The previously unknown HT-modifications will be structurally characterized. In summary one can say, that the proposal will make a significant contribution to our knowledge of the crystal chemistry of main group elements.