Site preferences and jump frequencies of In/Cd solutes in rare earth palladium phases having the L1 sub 2 structure
The method of Perturbed Angular Correlation of gamma rays (PAC) was used to study site preferences of indium solutes and jump frequencies of cadmium impurities in rare-earth palladium phases RPd sub 3 which has the L1 sub 2 structure (prototype AuCu sub 3), including both Pd-poorer and Pd-richer samples. It was found that indium solutes always occupied rare-earth sites in Pd-richer samples. In Pd-poorer samples, indium referentially occupied the rare-earth site for light rare-earth palladides (R=La and Ce), both rare-earth site and Pd-site for R=Ce, Pr, Nd, Sm and Eu, and almost entirely occupies the Pd site for R=Tb, Er, Yb and Lu. The sites occupied were resolved through measurements of the nuclear quadrupole interactions at super 111 In probe nuclei. For R=Ce, Pr, Nd, Sm and Eu, transfer enthalpies between R-sites and Pd-sites were determined through temperature dependences of the site fractions. The enthalpies were found to change sign along the series R=Ce, Pr, Nd, Sm and Eu, with indium solutes having lower enthalpy on rare-earth sites for R-Ce and on Pd-sites for R=Eu. For the series of rare-earth palladides, quadrupole interaction frequencies of cadmium impurities on Pd-sublattice were found to be ~110Mrad/s for intermediate and heavy rare-earth palladides. Surprisingly, the frequencies were observed to decrease along the series from R=Pr to Lu, in spite of a decrease on the lattice parameter. In addition, temperature dependences of the quadrupole interaction frequencies were found to be much greater for R=Pr than R=Lu. Quadrupole interaction frequencies of different L1 sub 2 phases were compared using a point charge model. Jump frequencies of cadmium impurities on the Pd-sublattice were determined from fits of nuclear relaxation for R=Ce, Pr, Nd, Sm and Eu, and activation enthalpies were extracted from Arrhenius temperature dependence of their jump frequencies. Activation enthalpies increases from 0.20 eV for R=Ce to 2.19 eV for R=Sm. Jump frequencies of rare-earth palladides were compared with those of observed in indides, gallides, aluminides, stannides and plumbides having the L1 sub 2 structure, and found to be generally the largest.