Particlelike versus wavelike phonon thermal transport across phase transition in NaNb O 3

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 (κ L) switching in NaNbO 3 across its ferroelectric (FE, R3c), AFE (Pca2 1), and paraelectric (PE, Pm-3m) phases. Results reveal sharp discontinuities in κ L at phase transitions, with a maximum switching ratio of 2.8 during the AFE–PE transition, governed primarily by particlelike conductivity (κ p) via abrupt phonon lifetime changes. Interestingly, in the Pca2 1 phase, wavelike conductivity (κ c) contributes up to 60% of κ 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 Pca2 1 phase suppresses phonon lifetimes, reducing κ p. These findings highlight the roles of κ p in phase-transition engineering of NaNbO 3 and κ c in strongly anharmonic systems, offering theoretical guidance for designing high-performance thermal switches via phase engineering.