Stabilizing digenite supercells amid Ni-doped off-stoichiometric bornite nanoparticles as a new approach for achieving ultra-low thermal conductivity

Applied Physics A: Materials Science and Processing. 2023. Vol. 129. Article 373 .

Lashkari A. H., Ostovari Moghaddam A., Shokuhfar A.

Nickel-doped off-stoichiometric bornite Cu5–xNixFeS3.71 0 ≤ x ≤ 1 nanoparticles were synthesized by high-energy mechanical alloying (MA) and subsequent annealing at 653 K for 1 h. X-ray diffraction (XRD) and differential scanning calorimetry (DSC) of the annealed powders revealed low-orthorhombic bornite as the main phase with a minor amount (< 2%) of digenite as the second phase. XRD analysis, scanning electron microscopy (SEM), and Energy-dispersive X-ray spectroscopy (EDS) results indicated that micro-sized digenite (Cu1.84S) supercells are formed amid bornite nanoparticles after hot-pressing at 673 K. Moreover, for Ni content of x = 0.08 and higher, about 2.6% of Ni3S2 precipitated as a third phase in Cu5–xNixFeS3.71 compounds, suggesting a solubility limit of x ≈ 0.08 for Ni in bornite. The thermal conductivity of the undoped pellet was 0.33 w/m.k at 325 K, which is about 30% lower than similar MA synthesized bornite. The lowest thermal conductivity was obtained for Cu4.96Ni0.04FeS3.71 (x = 0.04) at 473 K (0.19 w/m.k). This ultra-low thermal conductivity is attributed to the synergistic effect of bornite nanoparticles and micro-sized digenite supercells that highly increases phonon scattering at the interfaces. The maximum and minimum electrical resistivity at 325 K was obtained for x = 0.1 (0.106 mΩm) and x = 0.06 (0.137 mΩm) pellets.

Keywords: thermal conductivity, doping, Nanoparticles, Bornite, Off-stoichiometry