Experimental and theoretical determination of the Grüneisen parameter to analyze the density effect on anharmonicity and thermal conductivity in the NbCoSb system

The value of the thermal conductivity significantly depends on the point defect and anharmonicity of the material, and the strength of anharmonicity is given by the Grüneisen parameter (<i>γ</i>). Hence, the Grüneisen parameter is crucial to understanding the thermal conductivity of any material. In this work, the apparent Grüneisen parameter (<i>γ</i>_app) values for the defective half-Heusler compound are determined through combined theoretical and experimental approaches. The effect of both mass density and atomic density on <i>γ</i>_app is examined, with values ranging from 2.16 to 2.26 for different mass densities and from 1.64 to 2.40 for varying atomic densities. To gain further insight into thermal transport, the thermal conductivity of samples with different densities is measured. Using the experimentally determined <i>γ</i>_app, the thermal conductivity is calculated using Slack's equation. To ensure the reliability of the calculated Grüneisen parameter value, a thermal conductivity limited by Umklapp scattering is estimated by fitting the Debye-Callaway model. This work also highlights the influence of the mass and atomic density on the electron transport.