Effect of the cation sublattice composition of tin-based type-I clathrates on their low-temperature thermal properties

Abstract

We performed an experimental study on thermal properties of the Sn18In6As21.5I8 clathrate by measuring temperature dependencies of its heat capacity (2-300 K) and thermal expansion (5-300 K). By comparing the results with those published previously for Sn-based clathrates Sn24P19.2I8, Sn20Zn4P20.8I8, and Sn17Zn7P22I8, we established that partial replacement of tin and phosphorus by heavier indium and arsenic, respectively, leads to lowering vibration frequencies in both host and guest substructures. Deviation of the observed thermal properties at low temperatures from those predicted by the Einstein-Debye model is caused by the Schottky-like contribution of two-level systems to heat capacity and thermal expansion. These systems form owing to transitions of guest atoms in non-spherical 24-vertex cages between stationary states with close energies.

Single crystal synthesis and physical property of Ba8Cu1·0Ni2.5Ga10Si33.5 clathrate

“…Theoretical predictions suggested the involvement of electrons and holes together in the electrical conduction of this material. This behavior can be explained by considering that mobility, along with the concentration of holes and electrons, is closely linked to the nickel content and the intricate details of the material's band structure [ 28 ]. This observed metallic behavior aligns with the concept of holes as free charge carriers, as indicated by electron counting.…”

“…A distinct maximum near 12.1 K ( Fig. 10 (a)) can be attributed to Einstein vibration modes of the guest atoms [ 28 ]. At higher temperatures (50–300 K), together with the Einstein components of the heat capacity, the Debye component C D (T) begins to play an increasingly important role.…”

Ангармонизм колебаний решетки и тепловые свойства твердых растворов Сd-=SUB=-1-x-=/SUB=-Sr-=SUB=-x-=/SUB=-F-=SUB=-2-=/SUB=-

“…Заменяя классическую тепловую энергию k B T на среднюю энергию квантового осциллятора [19], рассматривая один дебаевский вклад акустических фононов и два вклада Эйнштейна для оптических фононов, аналогично [20,21], без учета влияния свободных электронов получаем…”