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.
