A Peculiar Site Preference of Boron in MgAl2-xBxO4 (x=0.0, 0.11, and 0.13) Spinel under High-Pressure and High-Temperature

作者：Yoshiasa Akira^*; Ito Tomokazu; Sugiyama Kazumasa; Nakatsuka Akihiko; Okube Maki; Kurosawa Masanori; Katsura Tomoo

来源：Zeitschrift fur Anorganische und Allgemeine Chemie, 2010, 636(3-4): 472-475.

DOI：10.1002/zaac.200900418

• High pressure spinet structure
• Magnesium
• Aluminum
• Boron
• X-ray diffraction
• Site occupancy

Single crystals of MgAl2-xBxO4 (x = 0.0, 0.11 and 0.13) spinet 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 B3+ 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 spinets are estimated as (Mg-0.47,Al-0.53)[Al-1.36,Mg-0.53,B-0.11]O-4 (x = 0.11) and (Mg-0.50,Al-0.50)-[Al-1.37,Mg-0.50,B-0.13]O-4 (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.

• 出版日期2010