Temperature dependence of the quadrupole interaction in potassium heptafluohafnate

The quadrupole interaction between the tantalum nucleus and its environment in potassium heptafluohafnate incorporating radioactive181Hf has been studied over the temperature range from 77 K to 318 K. A discontinuity in the field gradient tensor is observed at 250 K together with a more gradual alteration with midpoint temperature of approximately 210 K. Below 250 K, the data indicate two inequivalent sites for the tantalum nuclei. The values …