The scattering of non-equilibrium phonons on grain boundaries in single-phase ceramics

Studies of nonequilibrium phonon scattering on grain boundaries in single-p hase ceramics were made using the hear pulse method, when the temperature o f injected phonons exceeds the bath temperature only a little. The characte r of the scattering was determined from the temperature dependence of the h eat pulse signal maximum t(m). For AlN ceramics partial derivative t(m)/par tial derivative T < 0, which corresponds to the scattering of phonons on th in low acoustic impedance disordered interfaces between grains. After repea t annealing partial derivative t(m)/partial derivative t becomes positive b ecause of stabilization of grain boundaries and cattering on impurities and defects in the boundary regions. For SiC ceramics partial derivative t(m)/ partial derivative T < 0, but for the SiC-alpha samples t(m) similar to L-2 (L - the size of ceramic wafer) as predicted by theory, and for SiC-beta t he modification is t(m) similar to L-0.6 and this result is not fully under stood. (C) 1999 Elsevier Science B.V. All rights reserved.