Study on crystallographic and electronic structure of micrometre-scale ZnO and ZnO:B rods via X-ray absorption fine-structure spectroscopy.

X-ray absorption near-edge structure (XANES) and extended X-ray absorption fine-structure (EXAFS) spectra were recorded to investigate the electronic structure and local crystal structure of ZnO and ZnO:B powders produced via hydrothermal synthesis. ZnO and ZnO:B grow as micrometre-scale rods with hexagonal shape, as confirmed by scanning electron microscopy micrographs. The number of broken ZnO:B rods increases with increasing B concentration, as observed in the images, due to B atoms locating in between the Zn and O atoms which weakens and/or breaks the Zn-O bonds. However, no disorder within the crystallographic structure of ZnO upon B doping is observed from X-ray diffraction results, which were supported by EXAFS results. To determine the atomic locations of boron atoms in the crystal structure and their influence on the zinc atoms, EXAFS data were fitted with calculated spectra using the crystal structure parameters obtained from the crystallographic analysis of the samples. EXAFS data fitting and complementary k-weight analysis revealed the positions of the B atoms - their positions were determined to be in between the Zn and O atoms.

Probing local distortion around structural defects in half-Heusler thermoelectric NiZrSn alloy.

The half-Heusler NiZrSn (NZS) alloy is particularly interesting owing to its excellent thermoelectric properties, mechanical strength, and oxidation resistance. However, the experimentally investigated thermal conductivity of half-Heusler NZS alloys shows discrepancies when compared to the theoretical predictions. This study investigates the crystal structure around atomic defects by comparing experimental and theoretical X-ray absorption fine structure (XAFS) spectra of the crystal structure of a half-Heusler NZS alloy. The results of both Zr and Ni K-edge XAFS spectra verified the existence of atomic defects at the vacancy sites distorting the C1b-type crystal structure. We concluded that the distortion of the atoms around the interstitial Ni disorder could be the probable reason for the observed lower thermal conductivity values compared to that predicted theoretically in half-Heusler alloys. Our study makes a significant contribution to the literature because the detailed investigation of the lattice distortion around atomic defects will pave the way to further reduce the thermal conductivity by controlling this distortion.