The Quadrupolar Effect in Alkali Halide Mixed Crystals

Using NaBr–NaCl mixed crystals, we have observed the quadrupolar effect on the nuclear resonance absorption line of Na. The minority halogen plays the role of “impurity” or “solute” as in the case of alloys treated by Bloembergen and Rowland. The satellites of Na in NaCl are affected when the solute Br comes at the third halogen site counted from Na site, where the field gradient then becomes q ∼10 21 cm -3 . From our analysis the antishielding factor λ for Na is given as ∼10. The asymmetric broadening of the central line due to the second order perturbation occurs when and only when the solute comes next to the Na nucleus. The specimen being a single crystal, the satellites of the second order arise at the definite positions depending upon the direction and strength of the external magnetic field. By measuring this shift of the resonance field, we see that the field gradients produced then at the Na site are nearly 1.4×10 23 cm -3 and 2.0×10 23 cm -3 , when Br - and Cl - are the solute ion, respectively. On account of the segregation of the solute ions within the crystal, each Na site has rare chance to have more than one solute next to it.