Semiclathrates of the Ge–P–Te System: Synthesis and Crystal Structures

Abstract

Novel compounds [Ge(46-x) P(x) ]Te(y) (13.9≤x≤15.6, 5.92≤y≤7.75) with clathrate-like structures have been prepared and structurally characterized. They crystallize in the space group Fm ̅3 with the unit cell parameter changing from 20.544(2) to 20.698(2) Å (Z=8) on going from x=13.9 to x=15.6. Their crystal structure is composed of a covalently bonded Ge-P framework that hosts tellurium atoms in the guest positions and can be viewed as a peculiar variant of the type I clathrate superstructure. In contrast to the conventional type I clathrates, [Ge(46-x) P(x) ]Te(y) contain tricoordinated (3b) atoms and no vacancies in the framework positions. As a consequence of the transformation of the framework, the majority of the guest tellurium atoms form a single covalent bond with the host framework and thus the title compounds are the first representative of semiclathrates with covalent bonding. A comparison is made with silicon clathrates and the evolution of the crystal structure upon changing the tellurium content is discussed.

Low-temperature structure and lattice dynamics of the thermoelectric clathrate Sn24P19.3I8

“…Much lower thermal conductivity (below 1 W m −1 K −1 ) was reported for the Ge-based clathrates in the Ge-P-Te system. While these compounds were shown to possess less promising electrical transport properties, their structural flexibility implies that fine tuning of the power factor is possible by means of various substitutions both at the framework and guest positions [16,17]. Tin-based cationic type-I clathrates display even lower thermal conductivity ranging from 0.4 to 1.6 W m −1 K −1 at 298 K [8,[18][19][20][21].…”

Two New Arsenides, Eu7Cu44As23 and Sr7Cu44As23, With a New Filled Variety of the BaHg11 Structure

“…The preparation technique was essentially the same as in the synthesis of the A 2 Cu 6 P 5 compounds. 11 In a typical run, a stoichiometric mixture of the elements (ca. 3% excess of electropositive metal was used to compensate for its volatility) were enclosed into carbon-lined evacuated quartz tubes.…”

“…This brings about a possibility of optimizing these properties almost independently. Recently, the family of clathrates has been expanded by compounds showing peculiar superstructures of various clathrate structure types and also by clathrate-like compounds. − Importantly, some of these compounds do not contain any group 14 element, for example, Ba 8 Au 16 P 30 and Eu 2 Ba 6 Cu 16 P 30 . Although deviating from proper clathrates by composition and crystal structure, these compounds display properties that make them good candidates for creating new thermoelectric materials.…”

On the crystal structure of the germanium-based cationic clathrates [Ge38.3Sb7.7]I7.44, [Ge38.1P7.9]I8, and [Ge30.5Sn7.7P7.75]I7.88

“…They reported all these compounds to crystallize in the non centrosymmetric analog of the group Pm n, the space group P n, which was (in part) questioned later [17]. Recently, we showed that the Ge based cationic clath rates tend to have more complex structures, featuring superstructures, vacancy ordering, and formation of new clathrate types [18,19].…”