The local structures around Sb, Bi, and Ag dopant atoms in the environmentally friendly semiconductor Mg2Si were investigated by Sb K-edge, Bi L3-edge, and Ag K-edge x-ray absorption spectroscopy performed at 10 K. Fourier transforms (FTs) of the k3-weighted extended x-ray absorption fine structure (EXAFS) were analyzed. The experimental FTs of k3-weighted EXAFS were compared with the results of calculations using model clusters with Sb, Bi, and Ag atoms at the 8c, 4a, and 4b sites. The inverse FT of the χ(R) spectrum was calculated to refine the local structures for neighboring atoms around the Sb, Bi, and Ag atoms, and the interatomic distances and Debye–Waller factors were determined from the fit of the inverse FTs. The occupation of the 4a site by Sb and Bi atoms was demonstrated and that of the 8c site was investigated for Ag atoms. First-principles calculations were performed to clarify the characteristic change in the second-neighbor distances around the Ag atoms. The evaluation of the crystal orbital Hamilton population clarified that the change in the second-neighbor distances is caused by the bonding character formed between the Ag and Mg atoms. These results suggest that the Ag atoms mainly occupy the 8c site, while the large value of the Debye–Waller factor for the second neighboring atoms implies the possibility of the partial occupation of Ag atoms at the 4b sites. These findings provide an explanation for limiting the p-type conductivity in Mg2Si semiconductors.
The metathesis reaction between SnF4, ZnF2, and NaN3 under high pressure enabled the synthesis of ZnSnN2 crystals with a Zn/(Zn + Sn) ratio of 0.50. The crystal structure, optical bandgap, and carrier density of these stoichiometric ZnSnN2 crystals were investigated. X-ray diffraction profiles of the obtained powders coincided with those of a disordered wurtzite phase, regardless of the synthesis temperature and pressure. The electrical properties of the ZnSnN2 powders with stoichiometric metal compositions were studied after sintering under high pressure and temperature. The disordered wurtzite phase exhibited a bandgap of Eg = 0.7–1.2 eV, in reasonable agreement with theoretical predictions.
A $1∕2$ magnetization plateau in magnetic fields above 23 T and antiferromagnetic (AF) long-range order (AFLRO) in low fields were found in ${\mathrm{Cu}}_{2}{\mathrm{CdB}}_{2}{\mathrm{O}}_{6}$. Experimental results agree with quantum Monte Carlo results for an expected spin system. There are two kinds of Cu sites, [Cu(1) and Cu(2)], which are located adjacent to each other. Unexpectedly, spins on the Cu(1) and Cu(2) sites are in a nearly spin-singlet state and form AFLRO, respectively, although interactions between the Cu(1) and Cu(2) spins cannot be ignored. ${\mathrm{Cu}}_{2}{\mathrm{CdB}}_{2}{\mathrm{O}}_{6}$ is the first material which shows such coexistence in an atomic scale.
High-resolution ion mobility measurements have been performed for silicon cluster anions and cations, Sin− and Sin+, n=6–55. New isomers have been resolved for every cluster size larger than Si20. The results for the anions and the cations have the same global features. However, changing the charge often causes a shift in the isomer distribution, or causes new isomers to emerge. For example, the transition from prolate geometries to more-spherical ones is shifted to larger cluster sizes for the anions than for the cations. The mobilities of the anions are systematically smaller than those of the cations, presumably because of differences in the exterior electron densities.
