Reduction of the thermal conductivity of the thermoelectric material ScN by Nb alloying

ScN-rich (Sc,Nb)N solid solution thin films have been studied, motivated by the promising thermoelectric properties of ScN-based materials. Cubic Sc_1-xNb_xN films for 0 ≤ x ≤ 0.25 were epitaxially grown by DC reactive magnetron sputtering on a c-plane sapphire substrate and oriented along the (111) orientation. The crystal structure, morphology, thermal conductivity, and thermoelectric and electrical properties were investigated. The ScN reference film exhibited a Seebeck coefficient of −45 μV/K and a power factor of 6 × 10⁻⁴W/m K² at 750 K. Estimated from room temperature Hall measurements, all samples exhibit a high carrier density of the order of 10²¹ cm⁻³. Inclusion of heavy transition metals into ScN enables the reduction in thermal conductivity by an increase in phonon scattering. The Nb inserted ScN thin films exhibited a thermal conductivity lower than the value of the ScN reference (10.5 W m⁻¹ K⁻¹) down to a minimum value of 2.2 Wm⁻¹ K⁻¹. Insertion of Nb into ScN thus resulted in a reduction in thermal conductivity by a factor of ∼5 due to the mass contrast in ScN, which increases the phonon scattering in the material.