DETERMINATION OF THE ELECTRIC-FIELD GRADIENT IN RBCAF3 NEAR THE PHASE-TRANSITION

The fluoroperovskite, RbCaF3 undergoes a phase transition at 195.5K from a cubic to a tetragonal phase. The order parameter for this transition is directly related to the electric field gradient which arises in the tetragonal phase. In this work, we have used three NMR methods to measure the electric field gradient at the Rb-87 site in a single crystal of RbCaF3, very near this transition. These experiments are based on recent theoretical developments which allow the measurement of quadrupole parameters even for nuclei in a weak electric field gradient.