Site occupation of indium and jump frequencies of cadmium in FeGa 3
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Site occupation of indium and jump frequencies of cadmium in FeGa3 Randal Newhouse1 · Gary S. Collins1 · Matthew O. Zacate2
Published online: 27 September 2016 © Springer International Publishing Switzerland 2016
Abstract Perturbed angular correlation (PAC) measurements using the In-111 probe were carried out on FeGa3 as part of a broader investigation of indium site occupation and cadmium diffusion in intermetallic compounds. One PAC signal was observed with hyperfine parameters ω1 = 513.8(1) Mrad/s and η = 0.939(2) at room temperature. By comparison with quadrupole frequencies observed in PAC measurements on isostructural RuIn3 , it was determined that indium occupies only the 8j site in the FeGa3 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 jumppathways 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.
This article is part of the Topical Collection on Proceedings of the International Conference on Hyperfine Interactions and their Applications (HYPERFINE 2016), Leuven, Belgium, 3-8 July 2016 Matthew O. Zacate
[email protected] 1
Department of Physics and Astronomy, Washington State University, Pullman, WA, 99164, USA
2
Department of Physics, Geology, and Engineering Technology, Northern Kentucky University, Highland Heights, KY 41099, USA
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Hyperfine Interact (2016) 237: 137
Keywords TDPAC · Diffusion · Stochastic model · Iron-gallium alloy
1 Introduction Most intermetallic compounds are good conductors. A few however, such as FeGa3 , RuGa3 and RuIn3 are actually small bandgap semiconductors [1, 2]. The semiconducting nature of these compounds is thought to arise from greater than usual covalent bonding [3]. It is therefore of interest to investigate materials properties affected by cohesion in solids such as solute site occupation and diffusion jump rates. The present work examined site occupation of indium and jump frequencies of cadmium in FeGa3 using perturbed angular correlation spectroscopy (PAC). The crystal structure of FeGa3 (see Fig. 1) has been described in two different space groups [4, 5]. In the present work, the description from Ref. [5] is us
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