Anomalous hydrogen-hydrogen distances in metal hydrides

April 2, 2020
Anomalous hydrogen-hydrogen distances in metal hydrides
Visualization of the crystal structure of ZrV2H4. The atoms are represented by white (Zr), gold (V) and red (H) spheres. The anomalously small H-H distances are illustrated by the three H atoms shown connected by springs.

Scientific Achievement

Low energy vibrational features in ZrV2H4 reveal the presence of anomalous hydrogen-hydrogen (H-H) distances as short as 1.6 angstroms, much less than the decades old conventional limit in metal hydrides of 2.1 angstroms.

Significance and Impact

This work shows that the short H-H distances associated with near room temperature superconductivity in metal-hydrides at megabar pressures can actually be thermodynamically stable at ambient pressure.

Research Details

  • Inelastic neutron scattering from ZrV2Hx showed an unexpected peak around 50 meV with anomalous temperature dependence.  
  • Density Functional Theory (DFT) calculations of ZrV2H4 using the TITAN supercomputer showed that the spectral weight near 50 meV only arises for H-H distances < 2 Å

Inelastic neutron scattering maps below (left) and above (right) the superionic transition temperature of 475 K, showing the breakdown of the short-wavelength modes comprising the flat 3.5 meV feature at 300 K.