Site occupation of indium and jump frequencies of cadmium in FeGa3

TL;DR

This study used PAC measurements and density functional theory to investigate indium site occupation and cadmium jump frequencies in FeGa3, revealing indium's specific site preference and thermally activated cadmium diffusion with an activation energy of 1.8 eV.

Contribution

It provides the first detailed analysis of indium site occupation and cadmium jump dynamics in FeGa3 using combined experimental and theoretical approaches.

Findings

Indium exclusively occupies the 8j site in FeGa3.

Cadmium jump rates among Ga(2) sites are thermally activated.

Activation enthalpy for cadmium jumps is 1.8 eV.

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 w1 = 513.8(1) Mrad/s and eta = 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 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(1) eV.