Atomic jump frequencies in intermetallic compounds studied using perturbing angular correlation of gamma rays

Atomic jump frequencies were determined in a variety of intermetallic compounds through analysis of nuclear relaxation of spectra measured using the nuclear hyperfine technique, perturbed angular correlation (PAC) of gamma rays. Observed at higher temperatures, this relaxation is attributed to fluctuations in the orientation or magnitude of electric field gradients (EFG) at nuclei of 111In/Cd probe atoms as the atoms make diffusive jumps. Jump frequencies were obtained by fitting dynamically relaxed PAC spectra using either an empirical relaxation function or using ab initio relaxation models created using the program PolyPacFit. Jump frequency activation enthalpies were determined from measurements over a range of temperatures. Diffusion was studied in the following systems: 1) Pseudo-binary alloys having the L12 crystal structure such as In3(La1-xPrx). The goal was to see how jump frequencies were affected by random disorder. 2) The family of layered phases, LanCoIn3n+2 (n=0,1,2,3…∞). The goal was to see how jump frequencies varied with the spacing of Co layers, which were found to block diffusion. 3) Phases having the FeGa3 structure. The goal was to analyze dynamical relaxation for probe atoms having multiple inequivalent jump vectors. 4) Phases having the tetragonal Al4Ba structure. The goal was to search for effects in the PAC spectra caused by fluctuations in magnitudes of EFGs without fluctuations in orientations. Ab initio relaxation models were developed to simulate and fit dynamical relaxation for PAC spectra of FeGa3, and several phases with the Al4Ba structure in order to determine underlying microscopic jump frequencies. In the course of this work, site preferences also were observed for 111In/Cd probe atoms in several FeGa3 and Al4Ba phases

Atomic Jump Frequencies in Intermetallic Compounds Studied Using Perturbed Angular Correlation of Gamma Rays

Atomic jump frequencies were determined in a variety of intermetallic compounds through analysis of nuclear relaxation of spectra measured using the nuclear hyperfine technique, perturbed angular correlation (PAC) of gamma rays. Observed at higher temperatures, this relaxation is attributed to fluctuations in the orientation or magnitude of electric field gradients (EFG) at nuclei of 111In/Cd probe atoms as the atoms make diffusive jumps. Jump frequencies were obtained by fitting dynamically relaxed PAC spectra using either an empirical relaxation function or using ab initio relaxation models created using the program PolyPacFit. Jump frequency activation enthalpies were determined from measurements over a range of temperatures.Diffusion was studied in the following systems:1) Pseudo-binary alloys having the L12 crystal structure such as In3(La1-xPrx). The goal was to see how jump frequencies were affected by random disorder.2) The family of layered phases, LanCoIn3n+2 (n=0,1,2,3c). The goal was to see how jump frequencies varied with the spacing of Co layers, which were found to block diffusion.3) Phases having the FeGa3 structure. The goal was to analyze dynamical relaxation for probe atoms having multiple inequivalent jump vectors.4) Phases having the tetragonal Al4Ba structure. The goal was to search for effects in the PAC spectra caused by fluctuations in magnitudes of EFGs without fluctuations in orientations.Ab initio relaxation models were developed to simulate and fit dynamical relaxation for PAC spectra of FeGa3, and several phases with the Al4Ba structure in order to determine underlying microscopic jump frequencies. In the course of this work, site preferences also were observed for 111In/Cd probe atoms in several FeGa3 and Al4Ba phases

Atom jump frequencies of probe atoms in tin compounds

National Science Foundation grant DMR 90-04096 (Metals Program) Washington State University Department of PhysicsYin, X., Newhouse, R. and Collins, G. S. (2010, March 26). Atom jump frequencies of probe atoms in tin compounds. Poster presented at the Washington State University Academic Showcase, Pullman, WA

Site occupation of indium and jump frequencies of cadmium in FeGa3

Perturbed angular correlation (PAC) measurements using the In-111 probe were carried out on FeGa 3 as part of a broader investigation of indium site occupation and cadmium diffusion in intermetallic compounds. One PAC signal was observed with hyperfine parameters ω 1 = 513.8(1) Mrad/s and η = 0.939(2) at room temperature. By comparison with quadrupole frequencies observed in PAC measurements on isostructural RuIn 3 , it was determined that indium occupies only the 8j site in the FeGa 3 structure, denoted Ga(2) below because two out of the three Ga sites have this point symmetry. PAC spectra at elevated temperature exhibited damping characteristic of electric field gradients (EFGs) that fluctuate as Cd probes jump among Ga(2) sites within the lifetime of the excited PAC level. A stochastic model for the EFG fluctuations based on four conceivable, single-step jump-pathways connecting one Ga(2) site to neighboring Ga(2) sites was developed and used to fit PAC spectra. The four pathways lead to two observable EFG reorientation rates, and these reorientation rates were found to be strongly dependent on EFG orientation. Calculations using density functional theory were used to reduce the number of unknowns in the model with respect to EFG orientation. This made it possible to determine with reasonable precision the total jump rate of Cd among Ga(2) sites that correspond to a change in mirror plane orientation of site-symmetry. This total jump rate was found to be thermally activated with an activation enthalpy of 1.8 ±0.1 eV

Diffusion of Tracer Atoms in Al4Ba Phases Studied Using Perturbed Angular Correlation Spectroscopy

The Al4Ba crystal structure is the most common structure among binary intermetallic compounds. It is well suited for accommodating large atoms of group II elements and is often the intermediate phase closest to the terminal phase. It is, therefore, of interest to characterize diffusion properties of compounds with this tetragonal crystal structure. In the present study, 111In perturbed angular correlation spectroscopy was used to study solute site occupation and atom movement in In4Ba, Al4Ba, Al4Eu, Al4Sr, and Ga4Sr. The indium tracer and its daughter cadmium were found to occupy only the two Al-type sublattices in these compounds through detection of nuclear quadrupole interactions with axially symmetric EFGs. Measurements with increasing temperature revealed merging of signals due to dynamical averaging of these interactions as Cd atoms jumped at increasing rates between alternating sublattices. The jump rates were estimated to be between 8 kHz and 2 MHz at about 350 °C for Al4Eu and at about 450 °C for In4Ba and Al4Ba. Fits of spectra using Blume’s stochastic model allowed determination of activation enthalpies for average Cd jump rates between alternating Al sublattices in Al4Sr and Ga4Sr to be 1.16(3) eV and 1.47(3) eV, respectively. This result was used to estimate transverse diffusivities of Cd

Diffusion of Tracer Atoms in Al₄Ba Phases Studied Using Perturbed Angular Correlation Spectroscopy

The Al4Ba crystal structure is the most common structure among binary intermetallic compounds. It is well suited for accommodating large atoms of group II elements and is often the intermediate phase closest to the terminal phase. It is, therefore, of interest to characterize diffusion properties of compounds with this tetragonal crystal structure. In the present study, 111In perturbed angular correlation spectroscopy was used to study solute site occupation and atom movement in In4Ba, Al4Ba, Al4Eu, Al4Sr, and Ga4Sr. The indium tracer and its daughter cadmium were found to occupy only the two Al-type sublattices in these compounds through detection of nuclear quadrupole interactions with axially symmetric EFGs. Measurements with increasing temperature revealed merging of signals due to dynamical averaging of these interactions as Cd atoms jumped at increasing rates between alternating sublattices. The jump rates were estimated to be between 8 kHz and 2 MHz at about 350 °C for Al4Eu and at about 450 °C for In4Ba and Al4Ba. Fits of spectra using Blume’s stochastic model allowed determination of activation enthalpies for average Cd jump rates between alternating Al sublattices in Al4Sr and Ga4Sr to be 1.16(3) eV and 1.47(3) eV, respectively. This result was used to estimate transverse diffusivities of Cd