Effect of yttria on thermal transport and vibrational modes in yttria- stabilized hafnia
XZ Wang and JW Che and XY Liu, CERAMICS INTERNATIONAL, 48, 31705-31713 (2022).
Low thermal conductivity plays an essential role in application relevant to thermal energy conversion and management. In this paper, we utilize molecular dynamics to investigate the thermal transport and lattice variation modes in yttria-stabilized hafnia, which only contains binary oxides of Y2O3 and HfO2. It is found that the thermal conductivity kappa of yttria-stabilized hafnia decreases significantly with the increase of doping ratio of Y2O3, and then reaches a limiting value (similar to 2.1 W m(-1)K(-1)), because of the strong phonon scattering of oxygen vacancies. Importantly, a glass-like thermal conductivity kappa is achieved in yttria-stabilized hafnia samples when the content of Y2O3 exceeds 15 mol%. By decomposing the phonon vibrational modes, we find that most of the heat is transported by diffusive modes. As a result, the kappa exhibits a glass-like feature in yttria-stabilized hafnia samples with high content of Y2O3. Notably, the kappa of yttria- stabilized hafnia is much lower than those of classical functional ceramics materials. The insight into the kappa in yttria-stabilized hafnia system is beneficial for understanding and reducing the kappa of materials through defect engineering. Despite its simple composition, yttria-stabilized hafnia with different doping ratios demonstrates unexpected high scattering rate of phonon vibration density states, which is confirmed by the diffused wavevector-frequency dispersion. Eigenvector periodicity and phonon participation ratio of phonon have been visualized to capture the distribution of phonon modes in yttria- stabilized hafnia with various dopant. This work investigates into the details of phonon vibrational modes in yttria-stabilized hafnia, which would be valuable for conducting experiments to acquire low thermal conductivity materials in laboratory.
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