Papers by Keyword: Jump Frequency

Abstract: Diffusional jumps can produce fluctuating electric field gradients at nuclei of jumping atoms. Using perturbed angular correlation of gamma rays (PAC), jumps of probe atoms cause nuclear quadrupole relaxation that can be fitted to obtain the mean jump frequency. An overview is given of the application of this approach to highly ordered intermetallic compounds having the L1₂ (Cu₃Au) crystal structure. New results are then presented for jump frequencies of ¹¹¹In/Cd probe atoms in pseudo-binary L1₂ compounds of the forms In₃(La_1-xPr_x) and (In_1-xSn_x)₃La. For the mixed rare-earth system, jump frequencies are found to scale with composition between jump frequencies of the end-member phases In₃La and In₃Pr. However, for the mixed sp-element system, a large decrease in jump frequency is observed as Sn atoms substitute for In-atoms. This difference in behavior appears to depend on whether atomic disorder is on the diffusion sublattice (In-Sn substitution), as opposed to a neighboring sublattice (La-Pr substitution), whether or not there is a difference in diffusion mechanism between end-member phases, and/or whether or not there is a valence difference between the mixing atoms. All three conditions apply for only (In_1-xSn_x)₃La.

Abstract: Self-diffusion, both cationic and anionic diffusion, in ZnS nanoparticles is studied here following reaction coordinate theory. The jump frequencies, at various temperatures are computed. The isotope effect reveals the self-diffusion in nano ZnS is mainly through interstitial migration.

Abstract: Measurements were made of jump frequencies of ¹¹¹In/Cd tracer atoms on the Sn-sublattice in rare-earth tri-stannides having the L1₂ crystal structure via perturbed angular correlation spectroscopy (PAC). Phases studied were Sn₃R (R= La, Ce, Pr, Nd, Sm and Gd). Earlier measurements on isostructural rare-earth tri-indides showed that the dominant diffusion mechanism changed along that series [4]. The dominant mechanism was determined by comparing jump frequencies measured at opposing phase boundary compositions (that is, more In-rich and more In-poor). Jump frequencies were observed to be greater at the In-rich boundary composition in light lanthanide indides and greater at the In-poor boundary composition in heavy-lanthanide indides. These observations were attributed to predominance of diffusion via rare-earth vacancies in the former case and indium vacancies in the latter. Contrary to results for the indides, jump frequencies found in the present work are greater for the Sn-poor boundary compositions of the stannides, signaling that diffusive jumps are controlled by Sn-vacancies. Possible origins of these differences in diffusion mechanisms are discussed.

Abstract: Self-diffusion, both cationic and anionic, in ZnO nanoparticles was studied here in accord with reaction coordinate theory. The jump frequencies at various temperatures were computed. The isotope effect revealed that self-diffusion occurred mainly via a vacancy mechanism in nano ZnO; a result not previously reported in the literature.