Jean-Francois BISSON^1*, Hideki YAGI^1,2, Takakimi YANAGITANI², Alexander KAMINSKII³, Yuri N. BARABANENKOV⁴, and Ken-Ichi UEDA¹

¹Institute for Laser Science, University of Electro-Communications, 1-5-1 Chofu-gaoka, Chofu, Tokyo 182-8585, Japan
²Takuma Works, Konoshima Chemical Co., Ltd., 80 Kouda, Takuma, Mitoyo-gun, Kagawa 769-1103, Japan
³Institute of Crystallography, Russian Academy of Sciences, Crystal Laser Physics Laboratory, Leninsky pr. 59, Moscow 117333, Russia
⁴Institute of Radio Engineering and Electronics, Russian Academy of Sciences, Moscow 125009, Russia

(Received September 27, 2006; Accepted October 16, 2006)

Grain boundaries play a key role in determining several key properties of polycrystalline laser ceramics. Heat transfer measurements at low temperature constitute a good tool to probe grain boundaries. We review the results of heat transfer measurements in polycrystalline Y₃Al₅O₁₂ garnets as well as Y₂O₃ and Lu₂O₃ sesquioxide materials obtained by self-energy-driven sintering of nano-particles. The average phonon mean free path in Y₃Al₅O₁₂ was found to be significantly larger than the average grain size and to scale with temperature as T^-2 at low temperature. Existing models describing the interaction between phonons and grain boundaries are reviewed. Correct temperature dependence of the mean free path and order of magnitude of scattering rates were found by assuming the existence of a grain boundary layer having acoustic properties different from those of the bulk. A different temperature dependence of phonon mean free path was found for the sesquioxides and was ascribed to the stronger elastic anisotropy of these materials. The thermal resistance associated to the grain boundaries of laser ceramics was found to be lower than in other dense polycrystalline ceramic materials reported in the literature.

Key words: laser ceramics, garnets, sesquioxides, grain boundaries, thermal conductivity, phonons

^*E-mail address: Bisson@ils.uec.ac.jp