Fe and Cr K-edges EXAFS Study of Double Perovskite(Sr_(2-x)Ca_x)FeMoO_6(0 <=x <=2.0)and Sr_2CrMO_6(M=Mo,W)Systems

摘要

The local structure of the double perovskite(Sr_(2-x)Ca_x)FeMoO_6(0 <=x <=2.0)and Sr_2CrMO_6(M=Mo,W)systems have been probed by extended X-ray absorption fine structure(EXAFS)spectroscopy at the Fe and Cr K-edges.We found Fe-O(ave)distance apparently decreases from 1.999 A(x=0)to 1.991 A(x=1.0)in(Sr_(2-x)Ca_x)FeMoO_6(tetragonal structure).When x is increased further from 1.5 to 2.0,the Fe-O bond distance decreased from 2.034 A to 2.012 A(monoclinic structure).In addition,Cr-O,Sr-Cr,and Cr-Mo bond distances in Sr_2CrWO_6 are all slightly larger than the bond distances of Sr_2CrMoO_6,which is due to the ionic radius of the W~(5+)(0.62 A)which is larger than the ionic radius of Mo~(5+)(0.61 A).The results are consistent with our XRD refinements data.