Nd2O3·BaO·Al2O3·6B2O3的晶体结构

Nd_2O_3·BaO·Al_2O_3·6B_2O,晶体属六方晶体系,空间群为D_h-P62m晶胞参数a=4.566(2)A.Z=24.92(1)A,Z=1。由PW1100四园衍射仪收集到1460个独立衍射强度,用SNELX-76程序中的直接法解得晶体结构,全矩阵最小二乘方法修正结构参数,最后得到偏离因子R=8.80％(未校正吸收),全部计算在SORDCP/M-68K微处理机上完成,晶胞中2/3的B原于位于四面体内,形成B_2O_5]~4-团,另外1/3的B原子,连结33个O原子形成B_2O_3]中性团。由对称面联系的B_2O_3]团的B与B原子之间借助范德华键键合,结构上的这一特点,与硼酸铝钡钕晶体垂直C轴方向有明显解理性质完成一致。这一晶体的结构式可表示为Nd_2BaAl_2O_(1-x)B_2O_5]_4B_4O_(4+x+(2-x))]

CRYSTAL STRUCTURE OF Nd_2O_3.BaO.Al_2O_s.6B_2O_3

The crystal structure of Nd₂O₃·BaO·Al₂O₃·6B₂O₃ is hexagonal system, space group D_3h³-P62m with Z=1 and cell parameters a= 4.566(2)Å, c= 24.92(1)Å. The intensity data of 1460 independent reflections were obtained by using PW 1100 four-circle diffractometer. The crystal structure was determined by direct method with SHELX-76 program system and refined by full matrix least-squares technique to R-value of 8.80% for 1074 observable reflections. All calculations were carried out on miniproc essor of SORD CP/M-68K. Two-thirds of B atoms in unit cell sat in tetrahe-dral coordination makes the formula of bornate radical B₂O₅]^4- the other one-third of B atoms makes neutral group of B₂O₃]0 which links with other cations by Van der Waals bond. The obvious cleavage of Nd₂O₃·BaO·Al₂O₃·6B₂O₃ crystal perpendicular to c-axis can be explained by this structure characteristic. The structure formula of this crystal can be described by Nd₂BaAl₂O_1-xB₂O₅]₄B₄O_4+x+(2-x)].