Specific features of thermal phonon scattering and ferromagnetic properties of ZnO varistor ceramics

Abstract

The scattering of thermal phonons (T = 2.3-3.8 K) in ZnO single crystals and related 97.5ZnO + 0.5Bi 2 O 3 + 0.5Co 3 O 4 + 0.5MnO 2 + 1Sb 2 O 3 (mol %) ceramics has been studied. It is established that the transport characteristics of phonons with thermal frequencies in ceramics at liquid helium temperatures are determined by the presence of Co 2+ ions in ZnO grains. A model of phonon transport in ZnO based ceramics is proposed that takes into account the electron states of cobalt. The energy of the corresponding level is esti mated at Δ ≈ 5 K. Manifestations of the ferromagnetic effect are revealed.