Velocities of Longitudinal and Transverse Elastic Vibrations in Superionic Silver Sulfide
- PDF / 551,234 Bytes
- 6 Pages / 612 x 792 pts (letter) Page_size
- 98 Downloads / 154 Views
D MATTER
Velocities of Longitudinal and Transverse Elastic Vibrations in Superionic Silver Sulfide S. I. Sadovnikov* Institute of Solid State Chemistry, Ural Branch, Russian Academy of Sciences, Yekaterinburg, 620990 Russia *e-mail: [email protected] Received June 30, 2020; revised July 7, 2020; accepted July 7, 2020
It has been shown that the heat capacity of argentite β-Ag2S, which is nanocrystalline superionic silver sulfide, includes an additional positive contribution caused by the existence of the lower and upper bounds of the phonon spectrum because of a small size of particles. The estimate of this contribution from experimental data on the difference of the heat capacities of nano- and coarse-crystalline argentite β-Ag2S in the region of its existence 470–850 K makes it possible to determine for the first time the velocities of propagation of longitudinal and transverse elastic oscillations cl and ct and the elastic rigidity constants c11 , c12 , and c44 . It has been found that an increase in the temperature results in a decrease in the elastic characteristics of argentite. The directions of the crystal lattice of argentite corresponding to the maximum and minimum elastic moduli have been determined. DOI: 10.1134/S0021364020150096
Silver sulfide is a semiconductor below 450 K and a superionic conductor at temperatures from 452 to ~859 K. The superionic phase, which is called argentite β-Ag2S, has a bcc lattice (space group Im3 m). At temperatures from ~860 K to the melting temperature, the high-temperature fcc phase γ-Ag2S (space group Fm3 m) is stable. When bcc argentite β-Ag2S is cooled below 450 K, it undergoes a phase transition with the formation of monoclinic acanthite α-Ag2S, and when argentite is heated above ~850 K, a phase transition occurs with the formation γ-Ag2S [1–4]. The application of the most potentially promising argentite β-Ag2S in electronics requires information on its thermophysical and elastic properties in the temperature range of existence of argentite. The thermal expansion and heat capacity of coarse- and nanocrystalline silver sulfide were recently measured in the temperature range of 300–930 K [5–8], including the range of existence of argentite. Heteronanostructures based on semiconducting sulfides Ag2S and ZnS [9, 10], which allow controlling the width of the band gap and are considered as promising nanomaterials for ultraviolet solid-state lasers and fast resistance switches, attract a great amount of attention. In heteronanostructures (Ag2S)x(ZnS), the interface between silver and zinc sulfides plays an important role: deformation distortions at it should be minimal. To estimate these distortions, it is necessary to know the elastic characteristics of ZnS and Ag2S. The elastic properties of cubic ZnS are quite well
known [11], whereas data on the elastic properties of cubic Ag2S are absent. Four Ag atoms in the structure of cubic superionic sulfide silver β-Ag2S are statistically distributed over 54 6(b) and 48( j ) positions with the occupation probabilities of ~
Data Loading...
