Preparation and structure of NaSr0.5Al2B2O7 and NaCa0.5Al2B2O7 |
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Authors: | Jianhua Gao RK Li |
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Institution: | a Beijing Center for Crystal Research and Development, Technical Institute of Physics and Chemistry, Chinese Academy of Sciences, Beijing 100080, China b Graduate School of Chinese Academy of Sciences, China |
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Abstract: | Two compounds NaSr0.5Al2B2O7 and NaCa0.5Al2B2O7, have been found to crystallize into a new structure type by Rietveld refinement from X-ray powder diffraction data. Their structure belongs to hexagonal space group P63/m, with lattice parameters of , for NaSr0.5Al2B2O7 and , for NaCa0.5Al2B2O7, respectively. The structure is built up by Al2B2O7]2− double layer and Na+/Ca2+ or Na+/Sr2+ ions alternatively stacking along the c-axis. The sites in the inter-double layer are fully occupied jointly by Na and Ca or Sr, but the intra-double layer sites are only half occupied solely by Na. A mechanism of the transition of the structure from CaAl2B2O7 to present structure type by replacing only 1% Ca by Na (2%) as observed by Chang and Keszler (Mater. Res. Bull. 33 (1998) 299) is also proposed. |
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Keywords: | Alumino-borate Rietveld refinement Layered structure |
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