Hydrogen-induced reduction of electric field gradient in La_2Fe_(14)BH_x studied by NMR on ~(139)La

摘要

The ~(139)La NMR spin-echo spectra of La_2Fe_(14)BH_x are reported. Since lanthanum has no 4f electrons, the observed quadrupole splittings are directly proportional to the lattice part of the electric field gradient, V~(lat)_(zz). This quantity decreases as the content of interstitial hydrogen x grows. To describe the fall-off of V~(lat)_(zz), a dimensionless function f_2(x) is introduced, normalised so that f_2(0) = 1. Analysis of the new and earlier published data obtained by several experimental techniques demonstrates that the reduction of both the second-order crystal field parameter A_(20) and the lattice electric field gradient V~(lat)_(zz) is described by the same function f_2(x) in all R_2Fe_(14)BH_x. The only distinction that needs to be made is between R being a light and a heavy rare earth.