MgPt: Chemical Bonding Inhomogeneity and Structural Complexity.

MgPt represents the family of complex intermetallic compounds (complex metallic alloys, CMAs). It crystallizes in the cubic non-centrosymmetric space group 4̅3 with = 20.1068(2) Å and around 400 atoms in a predominantly ordered arrangement.

Local Atomic Arrangements and Band Structure of Boron Carbide.

Boron carbide, the simple chemical combination of boron and carbon, is one of the best-known binary ceramic materials. Despite that, a coherent description of its crystal structure and physical properties resembles one of the most challenging problems in materials science. By combining ab initio computational studies, precise crystal structure determination from diffraction experiments, and state-of-the-art high-resolution transmission electron microscopy imaging, this concerted investigation reveals hitherto unknown local structure modifications together with the known structural alterations.

Direct measurement of individual phonon lifetimes in the clathrate compound BaGeAu.

Engineering lattice thermal conductivity requires to control the heat carried by atomic vibration waves, the phonons. The key parameter for quantifying it is the phonon lifetime, limiting the travelling distance, whose determination is however at the limits of instrumental capabilities. Here, we show the achievement of a direct quantitative measurement of phonon lifetimes in a single crystal of the clathrate BaGeAu, renowned for its puzzling 'glass-like' thermal conductivity.

Nanodomain fragmentation and local rearrangements in CdSe under pressure.

Structural transformations in extended solids result from local atomic rearrangements and phase growth mechanisms. A broad class of technologically relevant properties critically depends on local structural issues connected with domain sizes, domain boundary geometries, and defects. However, a precise understanding of structural transformation mechanisms and domain formation is still an open question.

Crystal structure and local order in Co(6)Al(11-x)Si(6+x).

The ternary compound Co(6)Al(11-x)Si(6+x) (epsilon phase) was prepared from the elements by arc melting and subsequent heat treatment, and then characterized by single-crystal X-ray diffraction (XRD), electron-probe microanalysis (EPMA), differential thermal analysis (DTA) and transmission electron microscopy (TEM). This new structure type consists of planar layers with the composition [Co(6)Al(10)Si(4)], which are penetrated by perpendicular (Si-Si-Al) chains. While the layers are well described by an orthorhombic model (space group Pnma, Pearson symbol oP46), the chains exhibit doubled periodicity, thus yielding a superstructure.

A guest-free germanium clathrate.

The challenges associated with synthesizing expanded semiconductor frameworks with cage-like crystal structures continue to be of interest. Filled low-density germanium and silicon framework structures have distinct properties that address important issues in thermoelectric phonon glass-electron crystals, superconductivity and the possibility of Kondo insulators. Interest in empty framework structures of silicon and germanium is motivated by their predicted wide optical bandgaps of the same magnitude as quantum dots and porous silicon, making them and their alloys promising materials for silicon-based optoelectronic devices.