On the crystallochemical origin of the disordered form of Ba7(EuII)F12Cl2 and the structural changes induced at high temperature by F. Kubel and H. Hagemann

Crystal Research and Technology

Cryst. Res. Technol. 41, 1005 (2006) - Abstract -

On the crystallochemical origin of the disordered form of Ba₇^(EuII)F₁₂Cl₂ and the structural changes induced at high temperature

F. Kubel and H. Hagemann

Inst. für Chemische Technologien und Analytik, TU Wien, Getreidemarkt 9/164, A 1060 Vienna, Austria
*Dépt. de Chimie Physique, Univ. de Genève, 30, quai E. Ansermet, 1211 Geneva 4, Switzerland

Keywords	disordered solids, structural changes, luminescence
PACS	61.66.Fn, 81.30.-t, 61.43.-j, 78.60.-b
DOI	10.1002/crat.200610712

The crystal structure of the disordered modification of Ba₇F₁₂Cl₂ has been carefully re-examined on several new crystals prepared under different conditions of synthesis. All single crystal structure refinements reveal a residual electron density of ~3 e^-/Å³ in the 0,0,0 position which is explained by the introduction of a small amount of sodium ions in the crystal. The title compound transforms from a disordered to an ordered modification at ~800°C. New structural data show a change in space group from P6₃/m to P-6. During this process, a slight chemical change and the formation of nano-channels in the crystals is observed by electron microscopy. These changes were further studied by electron microprobe analysis, by spectroscopic methods and thermal analysis.

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