Ab-initio Structure Determination of the New Ion Conductor K2Al2O3F2 from Powder Diffraction Data

作者：Kubel Frank^*; Fleig Juergen; Pantazi Mariana; Januschewsky Judith

来源：Zeitschrift fur Anorganische und Allgemeine Chemie, 2011, 637(1): 41-45.

DOI：10.1002/zaac.201000240

• Aluminum
• Oxides
• Fluorine
• Ion conductors
• Ab initio structure determination
• Empirical energy calculations

The crystal structure of K2Al2O3F2, prepared at 800 degrees C by ceramic methods, was determined from conventional laboratory X-ray powder diffraction data. The compound crystallizes in the monoclinic space group C2/m (No. 12) with a = 11.21675(8), b = 8.16351(6), c = 6.12301(5) angstrom beta = 88.8108(6)degrees and Z = 4. Unit cell and space group suggestions were found by using the TOPAS program. Starting positional parameters for potassium and aluminum atoms were obtained from 548 reflections by the methods implemented in the FOX program. Oxygen and fluorine atom positions were determined by structural considerations. The structure was refined using the fundamental parameter approach of TOPAS, which gave the final residuals (%) R-Bragg = 1.6 and R-wp = 4.6. The crystal structure consists of individual layers of oxygen connected AlO3F tetrahedral groups with the fluorine atoms separating the layers. Empirical energy calculations agree with the crystal structure refinements and suggest no or little oxygen-fluorine exchange. Between and perpendicular to the sheets, the potassium ion can move without steric hindrance. Conductivity measurements from room temperature to 300 degrees C show decent potassium ion conductivity.

• 出版日期2011-1