Room temperature stable structures and phase transition of Na2Al2B2O7 |
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Authors: | JH Gao WB Xia |
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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 The Graduate University of Chinese Academy of Sciences, Beijing, China |
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Abstract: | By Rietveld refinement of the X-ray diffraction (XRD) data of powdered Na2Al2B2O7 samples aged for over 3 months, we found that Na2Al2B2O7 at room temperature is a mixture of two phases with space group and P63/m, respectively. The structures of the two phases can be refined with identical cell parameters of a=4.80760(11) Å, c=15.2684(5) Å and are composed by Al2B2O7]2−∝ double layers stacking alternatively with Na+ ions along the c-direction, but differ at in-plane bond orientations of the BO3/AlO4 groups within the double layers: in P63/m phase B-O1/Al-O1 bonds of the two layers are perfectly aligned, whereas in phase they are twisted by 46.4/41.6° around c-axis against each other. It is also found that a freshly prepared sample contains only the phase, but part of the phase will transfer to P63/m phase slowly at room temperature and the transition can be reversed by heating the aged sample above 220 °C. |
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Keywords: | A Inorganic compounds A Oxides C X-ray diffraction D Crystal structure D Phase transitions |
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