Thermal properties of boron and borides

Relationships between House Characteristics and Exposures to Metal(loid)s and Synthetic Organic Contaminants Evaluated Using Settled Indoor Dust

This study investigates associations between house characteristics and chemical contaminants in house dust, collected under the nationally representative Canadian House Dust Study (2007−2010). Vacuum samples (<80 µm fraction) were analysed for over 200 synthetic organic compounds and metal(loid)s. Spearman rank correlations between contaminant concentrations in dust and presence of children and pets, types of flooring, heating styles and other characteristics suggested a number of indoor sources, pointing to future research directions. Numerous synthetic organics were significantly associated with reported use of room deodorizers and with the presence of cats in the home. Hardwood flooring, which is a manufactured wood product, emerged as a source of metal(loid)s, phthalates, organophosphate flame retardants/plasticizers, and obsolete organochlorine pesticides such as ∑DDT (but not halogenated flame retardants). Many metal(loid)s were significantly correlated with flame-retardant compounds used in building materials and heating systems. Components of heating appliances and heat distribution systems appeared to contribute heat-resistant chemicals and alloys to settled dust. Carpets displayed a dual role as both a source and repository of dust-borne contaminants. Contaminant loadings (<80 µm fraction) were significantly elevated in heavily carpeted homes, particularly those located near industry. Depending on the chemical (and its source), the results show that increased dust mass loading may enrich or dilute chemical concentrations in dust. Research is needed to improve the characterisation of hidden indoor sources such as flame retardants used in building materials and heating systems, or undisclosed ingredients used in common household products, such as air fresheners and products used for companion animals.

Na3MgB37Si9: an icosahedral B12 cluster framework containing {Si8} units

Single crystals of a novel boride silicide, Na₃MgB₃₇Si₉, containing B₁₂ icosa­hedra and Si₈ units were synthesized from Na, B, Si, B₂O₃ and magnesium vapor.

Single crystals of a novel sodium–magnesium boride silicide, Na₃MgB₃₇Si₉ [a = 10.1630 (3) Å, c = 16.5742 (6) Å, space group Rm (No. 166)], were synthesized by heating a mixture of Na, Si and crystalline B with B₂O₃ flux in Mg vapor at 1373 K. The Mg atoms in the title compound are located at an inter­stitial site of the Dy_2.1B₃₇Si₉-type structure with an occupancy of 0.5. The (001) layers of B₁₂ icosa­hedra stack along the c-axis direction with shifting in the [–a/3, b/3, c/3] direction. A three-dimensional framework structure of the layers is formed via B—Si bonds and {Si₈} units of [Si]₃—Si—Si—[Si]₃.

Novel Principles and Nanostructuring Methods for Enhanced Thermoelectrics

Thermoelectrics (TE), the direct solid-state conversion of waste heat to electricity, is a promising field with potential wide-scale application for power generation. Intrinsic conflicts in the requirements for high electrical conductivity but (a) low thermal conductivity and (b) a large Seebeck coefficient have made enhancing TE performance difficult. Several recent striking advances in the field are reviewed. In regard to the former conflict, notable bottom-up nanostructuring methods for phonon-selective scattering are discovered, namely using nanosheets, dislocations, and most strikingly a process to fabricate nano-micropores leading to a 100% enhancement in the figure of merit (ZT ≈ 1.6) for rare-earth-free skutterudites. Porous materials are hitherto considered as having poor TE performance, so this is a new paradigm. In regard to the latter conflict, nanocomposite materials with hybrid effects and use of magnetism are emerging as novel bottom-up methods to enhance TE. Material informatics efforts to identify high-ZT materials are also reviewed.

The origin of the n-type behavior in rare earth borocarbide Y1−xB28.5C4

It was revealed that boron carbide inclusions were the origin of the p-type behavior in the Seebeck coefficient α previously observed for Y_1−xB_28.5C₄ in contrast to Y_1−xB_15.5CN and Y_1−xB₂₂C₂N, the long awaited n-type counterparts to boron carbide. Calculations show a pseudo gap-like structure in density of states and importance of the borocarbonitride network.

Complex borides based on AlLiB14 as high-temperature thermoelectric compounds

AlLiB₁₄ is examined as a potential high-temperature thermoelectric material.

Design Concepts for Improved Thermoelectric Materials

Some new guidelines are given that should be useful in the search for thermoelectric materials that are better than those currently available. In particular, clathrate and crypto-clathrate compounds with filler atoms in their cages offer the ability to substantially lower the lattice thermal conductivity.

The effect of transition metal doping on thermal conductivity of YB66

The effect of transition metal doping in YB66 has been studied with respect to increase its thermal conductivity. Single crystals of YB66 doped with 4th, 5th and 6th group transition metals were grown by floating zone method. A detailed structure analysis suggested that an existing special B—B pair at the (1/4, 1/4, 1/4) site of YB66 could be attributed to a phonon scattering center that causes the amorphous-like low thermal conductivity. It was found that 5th and 6th group transition metals of V, Cr, Nb and Mo substitute the B—B pair. By contrast 4th group transition metals such as Ti and Zr were found to enter another (x, x, x) site with x ∼ 0.135. Thermal conductivity of both Nb-doped and undoped YB66 was measured in the range 4 K ≤ T ≤ 150 K. Nb doping increased thermal conductivity of YB66 with a factor of about 2.