ENDOR evidence of noncubic distortion in Cs2NaYCl6:Ce

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Abstract
We have measured the ligand hyperfine coupling of 23Na and 133Cs nuclei nearest to paramagnetic Ce3+ ions in sites of octahedral symmetry in Cs2NaYCl6 using ENDOR. For 133Cs (I=7/2), an isotropic three line pattern was seen. The center line, at the free 133Cs resonance, arises from distant nuclei; the other lines could be fit by a spin Hamiltonian Hs =AsI⋅S with As= (49.7±3.0) kHz, S=1/2. The 23Na (I=3/2) spectrum exhibited a bulk sodium resonance and an additional pattern with (1) an anisotropic splitting ∼4 times larger than that expected on the basis of point dipolar coupling between the nearest nucleus and paramagnetic electron and (2) a slight departure from the axial symmetry expected from the room temperature cubic crystal structure of Cs2NaYCl6 and previous low temperature measurements. We believe this indicates a slight noncubic distortion of the crystal lattice, at least near the Ce3+ substitutional impurity.

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