Bournonite PbCuSbS3 : Stereochemically Active Lone-Pair Electrons that Induce Low Thermal Conductivity.

An understanding of the structural features and bonding of a particular material, and the properties these features impart on its physical characteristics, is essential in the search for new systems that are of technological interest. For several relevant applications, the design or discovery of low thermal conductivity materials is of great importance. We report on the synthesis, crystal structure, thermal conductivity, and electronic-structure calculations of one such material, PbCuSbS3 . Our analysis is presented in terms of a comparative study with Sb2 S3 , from which PbCuSbS3 can be derived through cation substitution. The measured low thermal conductivity of PbCuSbS3 is explained by the distortive environment of the Pb and Sb atoms from the stereochemically active lone-pair s(2) electrons and their pronounced repulsive interaction. Our investigation suggests a general approach for the design of materials for phase-change-memory, thermal-barrier, thermal-rectification and thermoelectric applications, as well as other functions for which low thermal conductivity is purposefully sought.

Precursor Routes to Complex Ternary Intermetallics: Single-Crystal and Microcrystalline Preparation of Clathrate-I Na8Al8Si38 from NaSi + NaAlSi.

Single crystals of the ternary clathrate-I Na8Al8Si38 were synthesized by kinetically controlled thermal decomposition (KCTD), and microcrystalline Na8Al8Si38 was synthesized by spark plasma sintering (SPS) using a NaSi + NaAlSi mixture as the precursor. Na8AlxSi46-x compositions with x ≤ 8 were also synthesized by SPS from precursor mixtures of different ratios. The crystal structure of Na8Al8Si38 was investigated using both Rietveld and single-crystal refinements. Temperature-dependent transport and UV/vis measurements were employed in the characterization of Na8Al8Si38, with diffuse-reflectance measurement indicating an indirect optical gap of 0.64 eV. Our results indicate that, when more than one precursor is used, both SPS and KCTD are effective methods for the synthesis of multinary inorganic phases that are not easily accessible by traditional solid-state synthesis or crystal growth techniques.

Synthesis, crystal structure, and transport properties of Cu2.2Zn0.8SnSe4-xTex (0.1 ≤ x ≤ 0.4).

Quaternary chalcogenides, particular compounds with the stannite structure-type, are of interest for thermoelectrics applications however tellurium-containing compositions have not been extensively investigated. We report on the synthesis and high temperature thermoelectric properties of p-type stannites Cu2.2Zn0.8SnSe4-xTex (x = 0.1, 0.2, 0.3, and 0.4). The compositions for each specimen were confirmed with a combination of Rietveld refinement and elemental analysis. Hall measurements indicate that holes are the dominant charge carriers in these materials. The electrical resistivity shows little temperature dependence up to 500 K and then increases with increasing temperature. The thermal conductivity decreases with increasing temperature with no indication of increase at higher temperatures suggesting a minimal bipolar diffusion effect in the thermal conductivity although these materials possess relatively small band-gaps as compared to that of other stannite compositions. A maximum ZT value of 0.56 was obtained at 700 K for Cu2.2Zn0.8SnSe3.7Te0.3 due to a relatively high Seebeck coefficient and low thermal conductivity.

Synthesis, crystal structure, and high temperature transport properties of p-type Cu2Zn(1-x)Fe(x)SnSe4.

Iron substituted Cu2Zn(1-x)Fe(x)SnSe4 stannites were synthesized by reaction of the constituent elements and subsequent annealing, followed by densification by hot-pressing. The compositions for each specimen were confirmed with a combination of Rietveld refinement and elemental analysis. Refinement results indicated that only the 2a site was occupied by Zn and Fe. High temperature transport properties were measured from 300 to 800 K. The electrical resistivity and thermal conductivity decrease with increasing Fe content. For the lower Fe content specimens with x = 0.2 and 0.4, the electrical properties are strongly temperature dependent, unlike that of the higher Fe content specimens (x = 0.6 and 0.8). A maximum ZT value of 0.46 was obtained at 800 K for Cu2Zn0.4Fe0.6SnSe4.

A new thiophosphate, Rb(0.38)Ag(0.5)Nb2PS10.

The structure of the new pentanary thiophosphate rubidium silver diniobium tris(disulfide) tetrathiophosphate, Rb(0.38)Ag(0.5)Nb2PS10, is made up of one-dimensional (infinity)1[Nb2PS10-] chains along the [001] direction. These chains are separated from one another by Ag+ and disordered Rb+ ions. The Nb2PS10- chain is built up from bicapped trigonal prismatic Nb(2)S(12) units which lie about inversion centres and tetrahedral PS4 groups. The Nb2S12 units are linked together to form linear Nb2S9 chains by sharing S-S prism edges. Short [2.898 (1) and 2.908 (1) A] and long [3.724 (1) A] Nb...Nb distances alternate along the chains, and S(2)2- and S2- anionic species co-exist in the structure. The Ag(+) cation lies on an inversion centre and has distorted octahedral coordination described as a [2+4]-bonding interaction.

Dicyano[[(1S)-(1-phenylethyl)aziridin-2-yl]methanolato-kappa2N,O]boron.

In the title compound, C(13)H(14)BN(3)O, the aziridine ring is an almost equilateral triangle, the C-C distance being slightly shorter than the C-N distances, probably because of the dative B-N bond. The five-membered ring, composed of two C atoms and N, B and O atoms, is fused with the aziridine ring to form a six-membered ring with a chair conformation.

A novel synthesis of 5-functionalized oxazolidin-2-ones from enantiomerically pure 2-substituted N-[(R)-(+)-alpha-methylbenzyl]aziridines.

5-Funtionalized enantiomerically pure oxazolidin-2-ones were prepared in one pot from commercially available chiral aziridines bearing an electron-withdrawing group at C-2 with retention of the configuration in high yields by regioselective aziridine ring-opening followed by intramolecular cyclization.