No abstract

A new modification of CuTi(2)S(4) was prepared from the elements at 425 degrees C. It crystallizes in the rhombohedral space group Rm, with lattice parameters of a = 7.0242(4) A, c = 34.834(4) A, and V = 1488.4(2) A(3) (Z = 12). Two topologically different interlayer regions exist between the close-packed S layers that alternate along the c axis: one comprises both Cu (in tetrahedral voids) and Ti atoms (in octahedral voids), and the second exclusively Ti atoms (again in octahedral voids). In contrast to the known modification, the spinel, Cu-Ti interactions of 2.88 A occur that have bonding character according to the electronic structure calculations. Both CuTi(2)S(4) modifications are metallic Pauli paramagnets due to Ti d contributions. The Pauli susceptibility of the Rm form is larger than that of the thiospinel in quantitative agreement with the LMTO-ASA band structure calculations. The irreversible transformation to the spinel takes place at temperatures above 450 degrees C.

A ternary sulfide exists on the quasi-binary section La 2 S 3 -Sb 2 S 3 , La 7+δ Sb 9-δ S 24 . This material exhibits a small but significant phase range with at least -0.296(4) e δ e 0.134(6). La 7+δ Sb 9-δ S 24 forms a new structure type, space group P2 1 /c, with a ) 8.7115(9) Å, b ) 14.3450(15) Å, c ) 15.2657(16) Å, β ) 90.105(2)°(Z ) 2) for δ ) 0.13. This structure contains chains of severely distorted SbS 5 square antiprisms, interconnected by eight-and nine-coordination La atoms. One position is mixed-occupied by La and Sb, with the La content ranging at least from 57% to 35%. La 7 Sb 9 S 24 is a blackish material with a computed gap >1.5 eV.

Mo 3 Sb 7 − x Te x is a high temperature thermoelectric material, reported to reach figure of merit (ZT)=0.8 at 1023 K. Various p-type samples of NiyMo3Sb7−xTex were prepared with y≤0.1 and 1.5≤x≤1.7 via high temperature reactions at 993 K. Adding transition metal atoms into the empty cube formed by Sb atoms significantly alters the band structure and thus the thermoelectric properties. Electronic band structure calculations indicate that adding Ni slightly increases the charge carrier concentration, while higher Te content causes a decrease. Thermoelectric properties were determined on pellets densified via hot pressing at 993 K. Seebeck as well as electrical and thermal conductivity measurements were performed up to 1023 K. The highest ZT value thus far was obtained from a sample of nominal composition Ni0.06Mo3Sb5.4Te1.6, which amounts to 0.93 at 1023 K.

These quaternary chalcogenides are isostructural, crystallizing in a unique structure type comprising localized Cu clusters and Te(2)(2-) dumbbells. With less than six Cu atoms per formula unit, these materials are p-type narrow-gap semiconductors, according to the balanced formula Ba(2+)(Cu(+))6Q(2-)(Te(2)(2-))3 with Q = S, Se. Encouraged by the outstanding thermoelectric performance of Cu(2-x)Se and the low thermal conductivity of cold-pressed BaCu(5.7)Se(0.6)Te(6.4), we determined the thermoelectric properties of hot-pressed pellets of BaCu(5.9)STe(6) and BaCu(5.9)SeTe(6). Both materials exhibit a high Seebeck coefficient and a low electrical conductivity, combined with very low thermal conductivity below 1 W m(-1) K(-1). Compared to the sulfide-telluride, the selenide-telluride exhibits higher electrical and thermal conductivity and comparable Seebeck coefficient, resulting in superior figure-of-merit values zT, exceeding 0.8 at relatively low temperatures, namely, around 600 K.

Hf5Sb9 was the first and thus far only example of an inorganic material that contains a pure T net, i.e. a planar layer of three‐bonded Sb atoms. It crystallizes in a super structure of the ZrSiS type, wherein the originally square layers are diluted and deformed to form said T net. Each Sb atom of this net, labeled Sb3, is connected to three symmetry equivalent Sb atoms at distances of about 3Å, reminiscent of molecular T examples such as BrF3. According to electronic structure calculations, these three Sb3–Sb3 interactions correspond to medium strong bonds. Hf5Sb9 is a high‐temperature antimonide that decomposes slowly under formation of HfSb2 at intermediate temperatures such as 750 °C, while it can be stored literally for years at room temperature. Like all other studied binary hafnium antimonides, Hf5Sb9 is metallic with a small Seebeck coefficient.

T time: The new binary antimonide Hf5Sb9 forms a unique variant of a square‐planar net, namely an unprecedented yet simple T‐shaped net (see picture, green) formed by antimony atoms (red). The electronic structure and bonding in the solid state are analyzed by theoretical methods.

ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract, please click on HTML or PDF.