Single crystals of MgAl2-xBxO4 (x = 0.0, 0.11 and 0.13) spinel were synthesized under high pressure (5 and 11 GPa) and high temperature (1873 and 1273 K) using a 1000 ton "6-8" type uniaxial split-sphere apparatus. Single-crystal X-ray diffraction measurements were carried out using a laboratory diffractometer with a Weissenberg-type imaging plate detector and using a four-circle diffractometer with synchrotron radiation at Photon Factory, Japan. The maximum content of boron was about x = 0.13 at 1273K and 11GPa. The smallest boron ion occupies the octahedral site in top priority in the spinel solid solution of the Mg/Al/B systems. The B 3+ ions can replace considerably bigger Al3+ ion under pressure. We estimated the cation distribution of each site from the reproduction of the observed, average distance using the observed local bond lengths for Mg-O and Al-O and the normal B-O distance. The chemical formula of boron-bearing spinels are estimated as (Mg0.47,Al0.53) [Al1.36Mg0.53,B0.11]O4 (x = 0.11) and (Mg0.50Al0.50)-[Al1.37,Mg 0.50B0.13]O4 (x = 0.13), respectively. These spinel solid solutions are largely disordered crystals and the inversion parameter grow up to 0.5 in the tetrahedral site. The temperature factor B eq for oxygen site in boron-bearing spinels were significantly larger than that in pure MgAl2O4 spinel. Only the positional shifts of oxygen ions have, therefore, been relaxing the disorder in structure.
|ジャーナル||Zeitschrift fur Anorganische und Allgemeine Chemie|
|出版ステータス||Published - 2010 3月 1|
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