We present a theoretical study of the structure and functionality of ferroelastic domain walls in tungsten trioxide, WO 3. WO 3 has a rich structural phase diagram, with the stability and properties of the various structural phases strongly affected both by temperature and by electron doping. The existence of superconductivity is of particular interest, with the underlying mechanism as of now not well understood. In addition, reports of enhanced superconductivity at structural domain walls are particularly intriguing. Focusing specifically on the orthorhombic β phase, we calculate the structure and properties of the domain walls both with and without electron doping. We use two theoretical approaches: Landau-Ginzburg theory, with free energies constructed from symmetry considerations and parameters extracted from our first-principles density functional calculations, and direct calculation using large-scale, GPU-enabled density functional theory. We find that the structure of the β-phase domain walls resembles that of the bulk tetragonal α 1 phase, and that the electronic charge tends to accumulate at the walls. Motivated by this finding, we perform ab initio computations of electronphonon coupling in the bulk α 1 structure and extract the superconducting critical temperatures, T c , within Bardeen-Cooper-Schrieffer theory. Our results provide insight into the experimentally observed unusual trend of decreasing T c with increasing electronic charge carrier concentration.

A BEC-type zeolite (polymorph C of zeolite beta) with low germanium content (Si : Ge = 5.1) has been synthesised using the flexible linear diquaternary cationic form of pentamethyldiethylenetriamine IJ2,2′-IJmethylazanediyl)bisIJN,N,N-trimethylethanammonium) as the organic structure-directing agent (SDA). The distribution of germanium within the framework and the location of the SDA within the pores have been determined by analysing synchrotron X-ray powder diffraction data collected on the as-synthesised form.The findings, which are corroborated by 13 C and 19 F NMR data, indicate that the structure of the SDA is retained during the synthesis and that the Ge atoms occupy only sites in the double 4-ring. Although the BEC framework structure has a three-dimensional 12-ring channel system, the SDA molecules are found to orient themselves in two dimensions along the channels running parallel to the a and b axes.