Tripling magnetite's thermoelectric figure of merit with rare earth doping

Abstract

Using density functional theory (DFT) and machine-learning force fields, we calculated the thermoelectric properties of magnetite doped with four rare-earth elements: lanthanum, cerium, praseodymium, and neodymium. Our results show that Fe₃O₄:Nd³⁺ exhibits the highest power factor (PF) of 6294 μW m⁻¹ K⁻² at 300 K when hole-doped at a concentration of 10²¹ cm⁻³. This remarkably high PF surpasses those reported in the literature for binary oxides and is a significant improvement upon the PF of pristine Fe₃O₄, which was calculated to be less than 4600 μW m⁻¹ K⁻² over a temperature range between 300 K and 900 K. More importantly, we predict a maximum thermoelectric figure of merit (ZT) of 0.76 at 800 K for Fe₃O₄:Nd³⁺, nearly triple the ZT of pristine Fe₃O₄ at the same temperature, with a 191.2% improvement. Our calculations offer a theoretical analysis of realistic expectations for thermoelectric enhancement by heavy but isovalent dopants in magnetic oxides, as Nd adopts a +3 oxidation state, being isovalent to the Fe it replaces, and is about three times heavier than Fe.