Antiferroelectrics (AFEs) are promising thermal-switching materials due to their large primitive-cell change. Using first-principles calculations combined with the temperature-dependent effective potential method and the Wigner transport equation, in this work, we systematically study lattice thermal conductivity (${\kappa }_L$) switching in $\mathrm{NaNb}{\mathrm{O}}_3$ across its ferroelectric (FE, $R3c$), AFE ($Pca{2}_1$), and paraelectric (PE, $Pm\text{−}3m$) phases. Results reveal sharp discontinuities in ${\kappa }_L$ at phase transitions, with a maximum switching ratio of 2.8 during the AFE–PE transition, governed primarily by particlelike conductivity (${\kappa }_p$) via abrupt phonon lifetime changes. Interestingly, in the $Pca{2}_1$ phase, wavelike conductivity (${\kappa }_c$) contributes up to 60% of ${\kappa }_L$, far exceeding its share (<25%) in other phases. The underlying mechanism is the strong coherent coupling among high-frequency near-degenerate phonon pairs. Meanwhile, the low symmetry of the $Pca{2}_1$ phase suppresses phonon lifetimes, reducing ${\kappa }_p$. These findings highlight the roles of ${\kappa }_p$ in phase-transition engineering of $\mathrm{NaNb}{\mathrm{O}}_3$ and ${\kappa }_c$ in strongly anharmonic systems, offering theoretical guidance for designing high-performance thermal switches via phase engineering.

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• Thermal conductivity
• Ferroelectrics
• Boltzmann theory