THE PREPARATION AND STRUCTURE OF THE ALPHA-QUARTZ AND BETA-QUARTZ POLYMORPHS OF BERYLLIUM FLUORIDE

Devitrification of vitreous BeF//2 at 355 degree C yields beta -quartz BeF//2 which on cooling to ambient temperature undergoes a displacive transition to give the alpha -quartz form. Both alpha - and beta -quartz BeF//2 have tetrahedral (BeF//4) structures which are very closely related to the corresponding SiO//2 polymorphs. At ambient temperature the Be-F bond lengths are 1. 541(2) and 1. 544(2) Angstrom and the Be-F-Be angle is 144. 6(2) degree . For beta -quartz BeF//2 at 246 degree C the corresponding average values in the micro-twinned structure are 1. 535 Angstrom and 150. 3 degree , respectively.