The electric quadrupole interaction of¹⁸¹Ta in Y₂O₃, CuO, and in the YBa₂Cu₃O_7−δ high temperature superconductors, doped with¹⁸¹Hf, has been studied by the time-differential perturbed angular correlation method (TDPAC). In Y₂O₃, two distinct fractions of the probe nuclei were detected, which were attributed to the substitutional positions at the two cation sites in the lattice. In CuO, and in the ceramic samples, broad distributions of quadrupole frequencies were observed. Possible configurations of the probe nuclei in these substances are discussed.