Anharmonicity in the Superionic Conductor AgCrSe2

April 2, 2020
Anharmonicity in the Superionic Conductor AgCrSe2
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.

Scientific Achievement

Long-wavelength transverse acoustic (TA) phonons coexist with ultrafast diffusing Ag ions in the high temperature superionic phase of AgCrSe2, while short-wavelength TA phonons break down. Extremely low thermal conductivity results from the Ag disorder and strong phonon interactions. 

Significance and Impact

The results exhibit how lattice dynamics affect the properties of superionic conducting materials that are important for improved thermoelectric and high-efficiency sold state electrolyte applications.

Research Details

Inelastic and quasi-elastic neutron scattering and inelastic X-ray scattering were used to characterize the ionic motions over a wide range of energy, momentum, and temperature.
First principles calculations corroborated the conclusions drawn from the experimental observations

“Anharmonic lattice dynamics and superionic transition in AgCrSe2,”
Jingxuan Ding1, Jennifer L. Niedziela2, Dipanshu Bansal3, Jiuling Wang1, Xing He1, Andrew F. May4, Georg Ehlers5, Douglas L. Abernathy6, Ayman Said7, Ahmet Alatas7, Yang Ren7, Gaurav Arya1, and Olivier Delairea8,9,1
Proceedings of the National Academy of Sciences USA 117, 3930 (2020) 
https://doi.org/10.1073/pnas.1913916117