High-frequency acoustic properties of yttrium ceramics
Abstract
The behavior of acoustic characteristics in yttrium ceramics is studied at a frequency of about 50 MHz. The temperature region above 30–40 K is characterized by pronounced hysteresis effects whose intensity is determined by the porosity of samples and the uniformity of their composition relative to oxygen. It is supposed that crystallite twinning due to additional stresses emerging in a sample is responsible for these effects. Possible mechanisms of emergence of such stresses are considered. At T < 20 K, the velocity of sound linearly increases with decreasing temperature, passes through a maximum at T∼ 1 K and then decreases. Such a behavior is typical of amorphous bodies and in all probability is due to the interaction between elastic waves and two-level systems.