Resonant scattering of nonequilibrium phonons (λ _ph = 10–50 nm) in nanostructured ceramics based on YSZ + Al₂O₃ composites

Abstract

Specific features of the transport of weakly nonequilibrium thermal phonons (λ _ph = 10–50 nm) in nanoscale ceramics at a transition from micro-to nanosizes have been investigated. On the basis of the model of spherical shells randomly distributed in space and modeling grain boundaries, whose elastic properties differ from the elastic properties of grains, features of the phonon spectrum in the wavelength range λ _ph ∼ R _g have been studied. The conditions leading to the occurrence of a gap in the phonon spectrum of nanoscale materials are analyzed. It is shown that the position of the top gap edge in the phonon spectrum is determined to a large extent by the structure of phase boundaries, while the presence of inclusions (pores, other phases) with characteristic sizes smaller than that of grains of the main ceramic material shifts the gap to high frequencies in the phonon spectrum. Temperature dependences of the diffusion coefficient of nonequilibrium phonons near the top gap edge in the phonon spectrum have been measured for multiphase ceramics based on YSZ + 14.3% Al₂O₃ composites.