ClathrateBa6Ge25:Thermodynamic, magnetic, and transport properties

Abstract

The recently discovered clathrate Ba 6 Ge 25 undergoes a two-step first-order phase transition at the temperatures T S1,S2 Ϸ215, 180 K. The first-order nature of the transition is evidenced from the hysteretical temperature dependences of the electrical resistivity (T), the Hall coefficient R H (T), and the magnetic susceptibility as well as from the temperature dependence of the specific heat. (T) increases drastically below T S1,S2

Crystal structure of barium europium germanide, Ba6-xEuxGe25 (x = 0.6), a chiral clathrate

“…Thus, the title compound is a Zintl phase with few conduction electrons. This is confirmed by the electrical resistivity data, showing metall-like behavior above 230 K. The transport properties of Ba 6-xEuxGe25 alloys are modified by europium insertion, and in comparison with Ba 6Ge25, the two-step first-order phase transition at T S1,S2 » 180 K, 220 K is quickly suppressed with increasing Eu content [11,12]. Ba/Eu1 Ba/Eu1…”

Effect of Helium Quasi-Hydrostatic Pressure on High-Pressure Behavior of Some Materials with Nano Spaces

“…X-ray diffraction patterns of Ba 24 Ge 100 at 250, 150 and 7 K under the pressure near 1.5 GPa. T s1 and T s2 correspond to the transition temperatures, which have been reported previously [11]. Fig.…”

Positional disorder of Ba in the thermoelectric germanium clathrate Ba6Ge25

“…Clathrates, in particular Ba 6 Ge 25 , have received much attention recently because of their potential as thermoelectric materials [1]. It has been argued that a good thermoelectric material should possess low thermal conductivity and high electric conductivity, i.e.…”

“…should share the characteristics of both "phonon gases" and "electron crystals" [2]. These two prerequisites are well met with Ba 6 Ge 25 in which electropositive Ba cations are enclosed within oversized cavities of a crystalline framework of covalently bonded Ge anions. The framework is 3D ordered and rigid, and provides a medium for high electrical conductivity of ~ 2000 S/cm [3].…”

“…A direct evidence for this rattling has come from diffraction experiments showing quite large values for the atomic displacement parameters of Ba atoms [3][4][5]. However, the electrical and thermal conductivity of Ba 6 Ge 25 change below room temperature spoiling material's thermoelectric characteristics. The change is due to a structural phase transition taking place between 180 -215 K [3,5,6].…”