Electron paramagnetic resonance spectra of Pr4+ ions doped in pyrochlore-type compounds La2Sn2O7 and La2Zr2O7

The electron paramagnetic resonance spectra of powders with the Pr4+ ions d oped in the B sites of the pyrochlore-type compounds A(2)B(2)O(7) (A = La; B = Sn or Zr) were successfully measured at 4.2 K, A very large hyperfine i nteraction with the Pr-141 nucleus was observed, The spectra mere isotropic , which indicates that the symmetry of the oxygen coordination around Pr4ions is almost octahedral. The results were analyzed based on the weak fiel d approximation, and the g values and hyperfine coupling constants A were o btained. The measured g values are smaller than /-10/7/ (which is calculate d for the Gamma(7) ground doublet in the F-2(5/2) multiplet), showing that the crystal held is effective to some extent on the behavior of a 4f electr on in solids. The value of /g/ decreases from 1.270 (Pr4+/La2Zr2O7) to 1.26 2 (Pr4+/La2Sn2O7), which is caused by the increase of the crystal field due to shrinking of the lattice, On the other hand, the hyperfine coupling con stants are the same: A = 0.076 (1) cm(-1). (C) 1999 Academic Press.