B.M. Garin, I.P. Nikitin, A.V. Taranov, E.N. Khazanov
The dielectric loss in the solid solutions (Y1-cLuc)3Al5O12 (YAG:Lu) c = 0...1 has been investigated in sub-millimeter frequency range. The direct connection between dielectric loss (DL) in sub-millimeter frequency range and UHF acoustic waves absorption has been revealed. The identity of concentration dependences of DL, acoustic waves absorption and Grüneisen constant implies that DL in YAG:Re at T = 300 K is two-phonon inherent lattice loss caused by lattice anharmonicity and corresponded to the minimal DL for that material. The obtained results are important for DL theory and relationship with acoustic phenomena. On the other hand, at low temperature two-phonon inherent lattice loss decreases considerably and DL is controlled by temperature-independent one-phonon processes. So one can expect that at low temperature the DL concentration dependence qualitatively matches the concentration dependence of non-equilibrium phonon scattering having minimum at c=0.25. That minimum is caused by structure «ordering» of YAG:Lu solid solutions.