Site preferences and jump frequencies of In/Cd solutes in rare earth palladium phases having the L1 sub 2 structure

This report includes the MS thesis of Qiaoming Wang, defended April 26, 2012. An addendum is attached at the end that provides additional information and results based on the research. The research described herein was supported in part by the National Science Foundation under grant DMR 09-04096 (Metals Program).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.National Science Foundation grant DMR 09-0409