Simulated Quadrupolar Broadening in Condensed Matter PAC Spectroscopy

Perturbed angular correlation (PAC) spectroscopy of materials containing static defects must often deal with quadrupolar broadening due to randomly distributed defects. The electric field gradient (EFG) due to defects adds to the crystal lattice EFG causing quadrupolar frequencies to differ from site to site in a crystal. We report a simulation study of the static defect EFG using a uniform random distribution of point charges. In this simulation, the distribution of random EFG's is found to depend on the ratio γ of the most probable values of the lattice and random EFG magnitudes, γ=Vzzlat/Vzzran. We present fits from the results of the simulations to Hf-doped cubic niobium and Nb-doped tetragonal ZrO2 PAC data. The single scaling parameter fitting for γ=0 provides an unprecedented excellent description for the cubic PAC data