PHASE-RELATIONS IN THE BAO-AL2O3-ALN SYSTEM - MATERIALS WITH THE BETA-ALUMINA STRUCTURE

It is generally known that aluminates with the beta-alumina-type struc ture exhibit very useful optical and electrical properties, In this pa per the synthesis of a new compound, namely barium aluminium-oxynitrid e with the beta-alumina structure (space group P6(3)/mmc) is reported. To obtain additional information, the BaO-Al2O3-AlN phase diagram was investigated at 1400, 1500, 1650, and 1700 degrees C. The ideal compo sition of this new material is BaAl11O16N. The unit cell dimensions of the material with the ideal composition (after firing at 1700 degrees C) are a = 5.6019 (2) Angstrom and c 22.6579 (8) Angstrom, so cia = 4 .0117 (2). We determined a solid solution between the already known ba rium beta-alumina (or barium hexaaluminate phase I) with the compositi on BaAl13.8O21.7 and the new barium aluminium-oxynitride. The extent o f this solid solution is dependent on the firing temperature. For this solid solution the c axis is decreasing, while the a axis is increasi ng with increasing nitrogen content. (C) 1997 Academic Press.