Temperature dependence of X-ray absorption and nuclear magnetic resonance spectra: probing quantum vibrations of light elements in oxides

A combined experimental-theoretical study on the temperature dependence of x-ray absorption near-edge structure (XANES) and nuclear magnetic resonance (NMR) spectra of periclase (MgO), spinel (MgAl 2 O 4), corundum (α-Al 2 O 3), berlinite (α-AlPO 4), stishovite and α-quartz (SiO 2) is reported. Predictive calculations are presented when experimental data are not available. For these light-element oxides, both experimental techniques detect systematic effects related to quantum thermal vibrations which are well reproduced by density-functional theory simulations. In calculations, thermal fluctuation of the nuclei are included by considering nonequilib-rium configurations according to finite-temperature quantum statistics at the quasiharmonic level. Nuclear quantum fluctuations on XANES and NMR spectroscopies are particularly sensitive to the coordination number of the probed cation. Furthermore, the relative importance of nuclear dynamics and thermal expansion is quantified over a large range of temperatures.