Machine—learning potential for higher-order scattering in two-dimensional PdTe2 allotropes

Significant variations in macroscopic properties are observed between allotropic phases of identical chemical composition. These variations have driven fundamental research into their structure-property correlations. In this work, the moment tensor potential (MTP) method is combined with phonon Boltzmann transport theory to systematically investigate the thermal transport properties of different PdTe₂ allotropes, including hexagonal PdTe₂ (H-PdTe₂), pentagonal PdTe₂ (P-PdTe₂), and β-phase PdTe₂ (β-PdTe₂). Considering only three-phonon scattering processes, all three allotropes of PdTe₂ exhibit low lattice thermal conductivity (\(\:{k}_{L}\)), with β-PdTe₂ possessing the lowest \(\:{k}_{L}\) due to the low phonon lifetime induced by the strong anharmonic scattering. Moreover, β-PdTe₂ shows pronounced anisotropic \(\:{k}_{L}\). Upon further accounting for higher-order phonon (four-phonon) scattering effects, \(\:{k}_{L}\) of β-PdTe₂ decreases by 32.16% (x direction) and 26.25% (y direction) at 300 K, reaching ultralow values of 3.35 W·m⁻¹·K⁻¹ (x) and 0.51 W·m⁻¹·K⁻¹ (y), respectively. Moreover, for H-PdTe₂, \(\:{k}_{L}\) decreases to 2.96 (x) and 2.96 W·m⁻¹·K⁻¹ (y) with a 12.92% reduction in both directions. For P-PdTe₂,\(\:{k}_{L}\) decreases to 1.82 W·m⁻¹·K⁻¹ (x) and 5.14 W·m⁻¹·K⁻¹ (y) with reductions of 23.23% and 35.01%, respectively. The significant suppression of thermal conductivity by four-phonon is attributed to the large four-phonon scattering phase space in the low frequency region. This work reveals the crucial role of higher-order anharmonicity and allotropic structure in achieving ultralow \(\:{k}_{L}\) in PdTe₂ allotropes, highlighting their significant potential for thermoelectric applications.