Crystal structure and Rietveld refinement of LaCo_2Al_8

The ternary compound LaCo2Al8 were prepared and studied by means of X-ray powder diffraction technique.The ternary compound LaCo2Al8 crystallizes in the orthorhombic CaCo2Al8-type structure with space group Pbam(No.55),the lattice parameters a=1.252 711(4) nm,b=1.441 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 Rietveld 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 Al 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.