Synthesis, extended and local crystal structure, and thermoelectric properties of Fe1-xRexGa3 solid solution
Résumé
We present a new Fe1–xRexGa3 solid solution, in which a 5d-metal––rhenium––partially substitutes for iron to the limiting composition of x = 0.10. The crystal structure refined for the composition Fe0.91Re0.09Ga3 shows the expected increase in the unit cell parameters compared to the parent FeGa3 compound, however the M–M (M = Fe, Re) distance decreases within the M–M dumbbell, indicating an increased M–M bonding density. Therein, investigation of the local structure by means of 69,71Ga NQR spectroscopy revealed the formation of homonuclear Fe–Fe and Re–Re dumbbells. Transport and thermoelectric properties have been investigated for the Re-substituted FeGa3. Electrical transport measurements showed preservation of the nonmetallic conductivity of Fe1–xRexGa3 despite the decrease of the valence electron concentration from 17 to 16.9 electrons per formula. At low temperatures, Fe1–xRexGa3 is a p-type semiconductor with the band gap of 0.4 eV, but with increasing temperature the sign of the dominant charge carriers changes. Owing to the alloying effect, Fe1–xRexGa3 displays 1.5 times lower thermal conductivity than FeGa3, which increases at high temperatures because of the growing contribution of the electronic term. © 2019