SODIUM AND OXYGEN DISORDER IN A SCANDIUM-SUBSTITUTED NASICON - A TIME OF FLIGHT NEUTRON POWDER DIFFRACTION STUDY OF NA2.5ZR1.8SC0.2SI1.3P1.7O12
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A Sc-substituted NASICON of composition Na2.5Zr1.8Sc0.2Si1.3P1.7O12 has been prepared and characterized by neutron powder diffraction and conductivity measurements. Time-of-flight neutron powder diffraction data were collected at 26, 100, 200, and 400C. Satisfactory Rietveld refinements were obtained for all temperatures using the rhombohedral space group R3c. The novel aspect of this structure is the simultaneous presence of partially occupied intersitial sodium and oxygen sites that are disordered with the regular Na(2) and O(1) sites in the known rhombohedral NASICON structure. The results are compared with recent findings of defect structures in other NASICON materials. Conductivity measurements in the range 30-350C reveal an activation energy of 0.30 eV for Na+ conduction but conductivity values were found to change with temperature of sample preparation. 1988.