Abstract: The chemical bond properties of the magnetoplumbite type compound LaMAl11O19(M＝Mg,Fe) have been studied by using the average band-gap model of the complex crystal chemical bond.The results show that covalency of La-O bond is only 3;,but 4f1 site has very high covalent character in each bond.The covalency for each bond obeys the following order:La-O＜Al(5)-O＜Al(1)-O＜Al(4)-O＜Al(2)-O＜Al(3)-O＜M-O.The anisotropy character in 2d site and 4e site of the crystals is revealed by calculating the chemical bond parameters.Mossbauer isomer shifts of Fe2+ ion in LaFeAl11O19 and Eu3+ ion in LaMgAl11O19 are calculated by using the chemical surrounding facter,h,definited by covalency and electronic polarizability,and the results are in agreement with the experimental values.

Key words: The chemical bond properties of the magnetoplumbite type compound LaMAl11O19(M＝Mg,Fe) have been studied by using the average band-gap model of the complex crystal chemical bond.The results show that covalency of La-O bond is only 3;,but 4f1 site has very high covalent character in each bond.The covalency for each bond obeys the following order:La-O＜Al(5)-O＜Al(1)-O＜Al(4)-O＜Al(2)-O＜Al(3)-O＜M-O.The anisotropy character in 2d site and 4e site of the crystals is revealed by calculating the chemical bond parameters.Mossbauer isomer shifts of Fe2+ ion in LaFeAl11O19 and Eu3+ ion in LaMgAl11O19 are calculated by using the chemical surrounding facter,h,definited by covalency and electronic polarizability,and the results are in agreement with the experimental values.