Distinguishing the Structures of High-Pressure Hydrides with Nuclear Magnetic Resonance Spectroscopy

Abstract

The structural characterization of high-pressure hydrides has encountered many difficulties mainly due to the weak X-ray scattering of hydrogen. Herein, we investigate the prospect of detecting the H3S and LaH10 structures with nuclear magnetic resonance (NMR) spectroscopy. Our calculations demonstrate that the different candidate structures of H3S (or LaH10) exhibit significant differences in the electric field gradient (EFG) tensor of the 33S (or 139La) sites, indicating that the NMR spectroscopy can well capture the structural differences, even the small changes in the atomic position, and hence can be used to effectively probe the structures and the phase transitions of H3S and LaH10. Our results clarify the relationship between the structures and the EFG tensor parameters and provide a potential means to detect the structures of high-pressure hydrides.

Enhancement of superconducting properties in the La–Ce–H system at moderate pressures

“…The XRD data revealed the common phase with P6 3 /mmc symmetry of the metal atoms, while the hydrogen positions cannot be directly determined due to a rather low scattering signal. The NMR technique will give more information on the structure of H-sublattice 48,49,50,51 but is limited by the synthesis conditions and sample dimension. We plotted our P-V data together with the calculated or experimental reported equations of state (EoS) of binary Ce-H and La-H hydrides for comparison (Fig.…”

Role of van der Waals forces in the metal–insulator transition of transition metal oxides

“…The EFG tensor parameters C Q and Z Q can well describe the change of electron distribution around the atomic states and can be measured by nuclear magnetic resonance (NMR) spectroscopy. [36][37][38][39][62][63][64] Therefore, the EFG tensor parameters have great prospects in understanding the charge ordering behaviors of TMOs. Table 4 shows that the M phase with one Fe atomic site is converted to the I phase with two Fe atomic sites accompanied by the increase of the C Q and Z Q values, indicating that the charge distribution becomes uneven and the structure becomes distorted, which well corresponds to the observed charge ordering behavior.…”

“…Furthermore, we study the electric field gradient (EFG) tensor parameters of CaFeO 3 to analyze its electronic structure. [36][37][38][39] According to the 57 Fe EFG tensor parameters, the metal phase with one Fe atomic site is converted to the insulating phase with two Fe atomic sites accompanied by the distortion of the structure, which is in line with the charge ordering behavior in the MIT of CaFeO 3 . 40…”