Direct observation of defect levels in hexagonal BN by soft X-ray absorption spectroscopy

Formation of defects in hexagonal boron nitride under low-energy argon bombardment has been studied by near-edge X-ray absorption fine structure (NEXAFS) around B and N K-edges. Breaking of B-N bonds and creation of nitrogen vacancies has been identified from the B K-edge, followed by the formation of molecular nitrogen, N2, at interstitial positions. The presence of N2 produces a sharp resonance in the low-resolution NEXAFS spectra around N K-edge, showing the characteristic vibrational fine structure in high-resolution measurements. Several new peaks in NEXAFS spectra have been assigned to boron or nitrogen interstitials, in good agreement with theoretical predictions. © 2009 Elsevier B.V. All rights reserved.

Stoichiometric changes in lithium conducting materials based on Li1+xAlxTi2−x(PO4)3: impedance, X-ray and NMR studies

The lithium fast-ion conductor, Li_1+xAl_xTi_2−x(PO₄)₃ (LATP) has been modified via changes in stoichiometry during the processing steps. The resultant changes have been followed using ²⁷Al MAS NMR, X-ray powder diffraction and impedance spectroscopy. The most important changes were those of the form Li_1.3+4yAl_0.3Ti_1.7−y(PO₄)₃. It was possible to remove the AlPO₄ phase (both tridymite and berlinite polymorphs), as monitored by X-ray diffractograms and ²⁷Al NMR spectra. Consequently, these changes appear to result in increased grain boundary conductivity of the LATP material.

High-pressure structural transitions of Sc2O3 by X-ray diffraction, raman spectra, and ab initio calculations

The high-pressure behavior of scandium oxide (Sc₂O₃) has been investigated by angle-dispersive synchrotron powder X-ray diffraction and Raman spectroscopy techniques in a diamond anvil cell up to 46.2 and 42 GPa, respectively. An irreversible structural transformation of Sc₂O₃ from the cubic phase to a monoclinic high-pressure phase was observed at 36 GPa. Subsequent ab initio calculations for Sc₂O₃ predicted the phase transition from the cubic to monoclinic phase but at a much lower pressure. The same calculations predicted a second phase transition at 77 GPa from the monoclinic to hexagonal phase.