Structural Chemical Studies of Gadolinium-and Erbium Compounds by Moessbauer Spectroscopy

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The Moessbauer effect of lanthanoid elements have been observed 14 elements, most of which is concerned with ^<151>Eu. For the other elements there are technical difficulties : we must make Moessbauer source by our self and cool both the source and sample at very low temperature. However we have succeeded in making a good narrow line source for ^<155>Gd and ^<166>Ed Moessbauer spectroscopy by neutron irradiation in nuclear reactor.We have measured those Moessbauer spectra at 12K of many kinds of complexes, solid solution, inter metallic comaounds and double oxides. The results have shown that the quadrupole coupling constant (e^2qQ) is verv useful aarameter for ^<155>Gd, and the effective magnetic field (H_<eff>) and the spin-spin relaxation time (τ) for ^<166>Ed.The e^2aQ values of (1-x)ZrO_2-xGdO_<1.5> increases with the increase of x in the ranse 0.18≦x≦0.50, reach maximum at x=0.5 (pyroclore structure) and then decrease in the range 0.50<x≦0.62. Since e^2qQ reflects the asymmetry of the charge distribution around the Gd nucleus, the asymmetry has been found to be the largest in the pyroclore structure of x=0.5. The parallel change of ^<155>Gd e^2qQ values of (1-x)ZrO_2-xGdO_<1.5> with that of ^<151>Eu isomer shift (δ) values of (1-y) ZrO_2-y EuO_<1.5> is observed which will be explained by the change of the M-O (M=Eu, Gd) bond length.The δ values of β-diketonatosadolinium (III) complexes fall in the very narrow range of 0.54-0.65mms^<-1>. Furthermore δ decrease in the order GdO_<6,7 or 8>>GdN_2O_<6 or7>>GdN_6O_2*, suggesting that δ decrease with the increase in the number of the nitrogen atoms coordinated to Gd ions.The spin-spin relaxation times of the seven coordinated β-diketonatoaqua erbium (III) complexes have been found to increase with the increase in the bulkiness of the β-diketons from their ^<>166Er Moessbauer saectra. The increase in the relaxation times is considered to originate from the lengthening of the distances between the Er^<3+> spins.