Thermoelectric technology, which possesses potential application in recycling industrial waste heat as energy, calls for novel high-performance materials. The systematic exploration of novel thermoelectric materials with excellent electronic transport properties is severely hindered by limited insight into the underlying bonding orbitals of atomic structures. Here we propose a simple yet successful strategy to discover and design high-performance layered thermoelectric materials through minimizing the crystal field splitting energy of orbitals to realize high orbital degeneracy. The approach naturally leads to design maps for optimizing the thermoelectric power factor through forming solid solutions and biaxial strain. Using this approach, we predict a series of potential thermoelectric candidates from layered CaAl2Si2-type Zintl compounds. Several of them contain nontoxic, low-cost and earth-abundant elements. Moreover, the approach can be extended to several other non-cubic materials, thereby substantially accelerating the screening and design of new thermoelectric materials.

The crystal structure of SnTe is investigated from 20 to 800 K in two samples with different carrier concentrations by single-crystal and powder synchrotron X-ray diffraction, coupled with maximum entropy analysis.

By taking into account the effects of domain structures and X-ray absorption, the superstructure of PbZrO3, lead zirconate, has been determined at room temperature. The space group is Pbam with a unit cell of a = 5.8884 (19), b = 11.771 (4) and c = 8.226 (3) Å, with Z = 8. The intensity data were collected using short-wavelength synchrotron X-rays of 0.350 Å; this reduces the linear absorption coefficient to 11.93 mm−1. The structure refinement was performed using only the data of superlattice reflections which are free from ambiguity and resulting from the domain structure; the final R value is 0.047 for 335 unique superlattice reflections. Zr atoms show the antiphase-type displacement along the z axis; oxygen octahedra show tilt of the type a − a − c 0 using Glazer's [Acta Cryst. (1972), B28, 3384–3392; Acta Cryst. (1975), A31, 756–762] notation.

Although crystalline solids are characterized by their periodic structures, some are only periodic on average and deviate on a local scale. Such disordered crystals with distinct local structures have unique properties arising from both collective and localized behaviour. Different local orderings can exist with identical average structures, making their differences hidden to Bragg diffraction methods. Using high-quality single-crystal X-ray diffuse scattering the local order in thermoelectric half-Heusler Nb1−x CoSb is investigated, for which different local orderings are observed. It is shown that the vacancy distribution follows a vacancy repulsion model and the crystal composition is found always to be close to x = 1/6 irrespective of nominal sample composition. However, the specific synthesis method controls the local order and thereby the thermoelectric properties thus providing a new frontier for tuning material properties.

The crystal structure of gismondite, a zeolite with narrow channels, has been refined using about 2200 F 0b8 gathered with a single-crystal diffractometer. All H 2 O molecules were located. The anisotropic refinement included determination of the Si/Al distribution and of site occupancies for the cation and 6 H 2 O equipoints. Although the Si and Al atoms are nearly ordered, the results suggest different arrange ments of H 2 O in otherwise identical cages. The final R w = 4.0% (conventional R = 5.5% ). 'Tphe crystal structure of natural gismondite from Hohenberg near Buehne/Westfalia was deduced by Fischer (4). The intensity data as well as the structure appeared to be suitable for a detailed refinement. Redetermination of the cell constants gave a = 9.843 ± 0.015; b = 10.023 ± 0.003; c = 10.616 ± 0.005 Α; γ = 92°25' ± 15' (first setting, space group V2 t /a). To obtain the Si/ΑΙ distribution as well as physi cally meaningful r.m.s. vibrational amplitudes, the set of Cu-K« intensities used for solving the structure had to be extended into the range of Mo-K« radiation (see Fischer, 5). Of the ca. 16,000 asymmetric reflections out side the Cu-Κα but within the Mo-K« range, about 250 were selected for measurement. After an intermediate stage of the refinement with copper data alone, structure factors and their contributions from the Si and Al atoms were computed for the Mo-Κα range. Reflections with both large F C ai and high contributions from the tetrahedral atoms were measured. Additional measurements were done with Mo-K<* radiation for about 50 reflections in the copper sphere for precise scaling. Furthermore, some 200 reflections were remeasured with Cu-K« radiation. All intensity data were gathered with a single-crystal diffractometer of the equi-inclination type (2, 6). The same crystal was used as in Ref. 4 (see also 9). The absorption correction employed a method patterned after Weber 250 Downloaded by UNIV OF CALIFORNIA SAN FRANCISCO on February 18, 2015 |