Ultrasonic investigation of amorphous As 2 S 3 from 1.5 to 480 K

摘要: The attenuation of longitudinal and shear ultrasonic waves with frequencies between 10 450 MHz has been measured in amorphous ${\mathrm{As}}_{2}$${\mathrm{S}}_{3}$ at various temperatures 1.5 480 K. It is found that the proportional to frequency except below about 30 K where it becomes less dependent lower temperature. Below 50 accounted for quantitatively using recent theory due stress-relaxation processes each which involves thermal phonon-assisted tunneling a sulfur ion adjacent positions representable by double potential-energy well. Tunneling times wide range values occur indicating there are wells barrier heights amounts asymmetry. probability occurrence be product two Gaussian distributions depending, respectively, on size energy difference given pair. number per unit volume deduced from fitting our data consistent density deducible low-temperature specific-heat Stephens. Direct evidence electronic not responsible obtained measurements revealed 4.2 increased only very slightly magnetic field up highest value used, 133 kOe. Between 140 almost independent temperature may combined effects ions through hopping over potential barriers many material although no quantitative justification this presented. Above increase an ever increasing rate 30-MHz longitudinal-wave can fitted fairly well all way three-term expression terms being exponential functions negative reciprocal Various possible interpretations these results presented but unique definitive explanation arrived at. However, does seem more than one type relaxation process characterized times. Jumping groups involved. velocites 10-, 30-, 50-MHz 10- have also $a\ensuremath{-}{\mathrm{As}}_{2}{\mathrm{S}}_{3}$ samples 100 290 velocities both types as decreases manner attributable anharmonicity interatomic forces. thereby providing additional Akhieser phonon viscosity mechanism usually predominates crystalline dielectric solids question.