Diffusion in Intermetallic Compounds Studied Using Nuclear Quadrupole Relaxation

2005 ◽  
Vol 237-240 ◽  
pp. 195-200 ◽  
Author(s):  
Gary S. Collins ◽  
A. Favrot ◽  
L. Kang ◽  
D. Solodovnikov ◽  
Matthew O. Zacate
Keyword(s):  
Intermetallic Compounds ◽  
Gamma Rays ◽  
Perturbed Angular Correlation ◽  
Nuclear Quadrupole Interaction ◽  
Jump Frequency ◽  
Quadrupole Relaxation ◽  
Boundary Composition ◽  
Nuclear Quadrupole ◽  
Jump Frequencies ◽  
Nuclear Quadrupole Relaxation

The jump frequency of Cd tracer atoms was measured as a function of temperature in seven rare-earth tri-indide intermetallic compounds having the L12, or Cu3Au, structure. The frequency, proportional to the diffusivity, was detected by relaxation of nuclear quadrupole interaction at Cd nuclei caused by reorientation of the electric field gradient in each diffusive jump. Measurements were made using perturbed angular correlation of gamma rays, sensitive to jump frequencies in the range 1-1000 MHz. Results are as follows. (1) Jump frequencies measured in LaIn3 and CeIn3 were observed to be 10-100 times greater at the more In-rich boundary composition than the less In-rich boundary composition, even though the phases appear as line compounds in phase diagrams. (2) Arrhenius plots of the jump frequency were fitted to activation enthalpies that increase from 0.535 to 1.80 eV across the series of phases LaIn3, CeIn3, PrIn3, and NdIn3.

Motion of Cadmium Tracer Atoms in Al11R3 Phases (R=La,Ce,Pr)

2009 ◽  
Vol 289-292 ◽  
pp. 755-761 ◽  
Author(s):  
Stephanie Lage ◽  
Gary S. Collins
Keyword(s):  
Gamma Rays ◽  
Time Domain ◽  
Perturbed Angular Correlation ◽  
Nuclear Quadrupole Interaction ◽  
Electric Field Gradients ◽  
Jump Frequency ◽  
Field Gradients ◽  
The Mean ◽  
Nuclear Quadrupole ◽  
Jump Frequencies

Jump frequencies of Cd tracer atoms were measured in three phases having the orthorhombic Al11R3 structure, with R= La, Ce, or Pr. The structure has four inequivalent Al-sites and two inequivalent R-sites. 111In/Cd tracer atoms were observed to occupy several sites via the nuclear quadrupole interaction using perturbed angular correlation of gamma rays (PAC). Time-domain PAC spectra became damped as the temperature increased, which is attributed to nuclear relaxation caused by diffusional jumps of Cd tracer atoms leading to changes in orientations and/or magnitudes of electric field gradients (EFG’s). Maximum relaxations were observed near 770 K. A method is proposed for estimating the mean jump frequency at that temperature, giving a mean jump frequency w averaged over all sites of about 100 MHz. At still higher temperatures, damping decreased due to motional averaging, and the quadrupole perturbations evolved into unique signals having lower frequencies and corresponding in each phase to the averages of EFG tensors of all sites visited by the Cd tracer atoms. For Al11La3, the jump frequency at 1073 K was estimated to be 1.9 GHz. Such jump frequencies imply unusually high diffusivities in these phases.

scholarly journals Diffusion in LanCoIn3n+2 Phases Studied by Perturbed Angular Correlation

2012 ◽  
Vol 323-325 ◽  
pp. 453-458 ◽  
Author(s):  
Randal Newhouse ◽  
Gary S. Collins
Keyword(s):  
Angular Correlation ◽  
Perturbed Angular Correlation ◽  
Diffusion Mechanism ◽  
The Other ◽  
Electric Field Gradients ◽  
Jump Frequency ◽  
Quadrupole Relaxation ◽  
Field Gradients ◽  
Jump Frequencies ◽  
Nuclear Quadrupole Relaxation

Jump frequencies of 111In/Cd tracer atoms were measured for a series of layered phases LanCoIn3n+2 using the technique of perturbed angular correlation of gamma rays (PAC). The frequencies were determined by analysis of nuclear quadrupole relaxation produced by fluctuating electric field gradients. Samples were synthesized having nominal values n= 1, 2, 3, 5 and , with n= corresponding to the L12 phase LaIn3. The phases form heuristically from LaIn3 by replacing every (n+1)th (100) mixed plane of La and In atoms with a plane of Co-atoms. For the n=1 phase, LaCoIn5, jump frequencies were too small to detect. Two signals were observed, one for indium atoms next to the Co-planes and the other for more distant indium atoms. No relaxation was observed for atoms next to the Co-planes, indicating that there is no diffusion across the Co-planes. With increasing n, jump rates for the other In-atoms increased toward values observed for LaIn3. Jump frequency activation enthalpies for n= 3 and 5 were observed to be the same as for n=, suggesting the same diffusion mechanism. However, the jump-frequency prefactors were found to be smaller for small n, which is attributed to reductions in the connectivity of the diffusion sublattice. We conclude that diffusion in the layered phases is remarkably similar to diffusion in LaIn3 once the reduced connectivity is taken into account.

scholarly journals Diffusion in Binary and Pseudo-Binary L12 Indides, Stannides, Gallides and Aluminides of Rare-Earth Elements as Studied Using Perturbed Angular Correlation of 111In/Cd

2012 ◽  
Vol 323-325 ◽  
pp. 447-452
Author(s):  
Randal Newhouse ◽  
Justine Minish ◽  
Gary S. Collins
Keyword(s):  
Rare Earth ◽  
Angular Correlation ◽  
Perturbed Angular Correlation ◽  
Diffusion Mechanism ◽  
Jump Frequency ◽  
Quadrupole Relaxation ◽  
System A ◽  
Field Gradients ◽  
Ordered Intermetallic ◽  
Jump Frequencies

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 of111In/Cd probe atoms in pseudo-binary L12compounds of the forms In3(La1-xPrx) and (In1-xSnx)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 (In1-xSnx)3La.

Jump Frequencies of Cd Tracer Atoms in L12 Lanthanide Gallides

2009 ◽  
Vol 289-292 ◽  
pp. 725-732 ◽  
Author(s):  
Xia Jiang ◽  
Matthew O. Zacate ◽  
Gary S. Collins
Keyword(s):  
Gamma Rays ◽  
Elevated Temperatures ◽  
Physical Review ◽  
Nuclear Quadrupole Interaction ◽  
Electric Field Gradients ◽  
Jump Frequency ◽  
Perturbation Functions ◽  
Field Gradients ◽  
Jump Frequencies ◽  
L12 Structure

Jump frequencies of Cd tracer atoms were measured in three lanthanide gallides having the L12 structure: DyGa3, ErGa3 and LuGa3. 111In/Cd impurity probe atoms were observed to occupy the non-cubic Ga-sites through the nuclear quadrupole interaction using the method of perturbed angular correlation of gamma rays (PAC). Measurements at elevated temperatures exhibited nuclear relaxation (damping) of quadrupolar perturbation functions attributed to diffusional jumps of the probes among orientationally inequivalent Ga-sites. Accurate values of jump frequencies were determined from fits of the measured perturbation functions using a model of stochastically fluctuating electric-field gradients, as in previous work [e.g., Matthew O. Zacate, Aurélie Favrot and Gary S. Collins: Physical Review Letters Vol. 92 (2004) p. 225901]. Arrhenius plots of jump frequencies for the three systems exhibited jump-frequency activation enthalpies in the range 0.86-1.05 eV and prefactors of about 2 THz. The activation enthalpy for ErGa3, 0.86(2) eV is compared with those for ErAl3, 1.40(4) eV, and ErIn3, 1.34(5) eV.

Jump Frequency of Cd Tracer Atoms in β-Mn

2005 ◽  
Vol 237-240 ◽  
pp. 396-401 ◽  
Author(s):  
Matthew O. Zacate ◽  
Gary S. Collins
Keyword(s):  
Angular Correlation ◽  
Gamma Rays ◽  
Polymorphic Transformation ◽  
Perturbed Angular Correlation ◽  
Activation Enthalpy ◽  
Jump Frequency ◽  
Quadrupole Relaxation ◽  
Kinetics Of

The jump frequency of Cd tracer atoms in pure and Al-doped b-Mn was determined from measurements of quadrupole relaxation using the method of perturbed angular correlation of gamma rays. The jump frequency of Cd in b-Mn containing about 4.5 at.% Al had an activation enthalpy of 0.67(3) eV. In pure b-Mn at 950 K, the jump frequency was a factor about 8 larger than the value of 9.2 MHz in the alloy. Information was also obtained about the sluggish kinetics of the a-Mn to b-Mn polymorphic transformation.

scholarly journals Comparison of Jump Frequencies of 111In/Cd Tracer Atoms in Sn3R and In3R Phases Having the L12 Structure (R = Rare-Earth)

2011 ◽  
Vol 311 ◽  
pp. 159-166 ◽  
Author(s):  
Megan Lockwood Harberts ◽  
Benjamin Norman ◽  
Randal Newhouse ◽  
Gary S. Collins
Keyword(s):  
Rare Earth ◽  
Perturbed Angular Correlation ◽  
Diffusion Mechanism ◽  
Correlation Spectroscopy ◽  
Perturbed Angular Correlation Spectroscopy ◽  
Dominant Mechanism ◽  
Boundary Composition ◽  
Light Lanthanide ◽  
Diffusion Mechanisms ◽  
Jump Frequencies

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.

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