化合物LaCo_2Al_8的晶体结构及其Rietveld精修

Crystal structure and Rietveld refinement of LaCo_2Al_8

利用X射线粉末衍射技术和Rietveld结构修正方法对LaCo2Al8进行了研究,结果表明,化合物LaCo2Al8具有正交CaCo2Al8结构类型,空间群为Pbam(No.55),点阵参数为a=1.252 711(4)nm,b=1.441 71(5)nm,c=0.404 22(1)nm,指标化的可靠性因子为152.0(45)。采用Rietveld结构修正法对化合物LaCo2Al8的晶体结构成功地进行了精化修正,精修所得的R因子为Rp=0.096,Rwp=0.124。在正交结构中,La占据4g位置,Co原子占据2种4g位置,Al原子则分别占据5种4h位置、2种4g位置及2d和2a位置。化合物LaCo2Al8的原子间合理的键长说明了Rietveld精修得到的结构的合理性。

The ternary compound LaCo2Al8 were prepared and studied by means of X-ray powder diffraction technique. The ternary compound LaCo2AIs crystallizes in the orthorhombic LaCo2Al8-type structure with space group Pbam （No. 55）, the lattice parameters a = 1.252 711 （4） nm, b = I. 441 71 （5） nm, c = 0. 404 22（ 1 ）nm. The Smith and Snyder figure of merit is 152. 0 （45）. The crystal structural refinement of the compound LaCo2Al8 was successfully performed by using Ri- etveld method from the X-ray diffraction data. The R-factors of Rietveld refinement are Rp = 0. 096 and Rwp = 0. 124, respectively. In the orthorhombic structure, La atoms occupy the 4g sites and Co atoms are located at other two different 4g sites, while A1 atoms are at the five 4h, two 4g, 2d and 2a sites, respectively. The reasonable bond lengths indicated that the obtained refined structure is correct.