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Compressed cesium polyhydrides: Cs+ sublattices and H3(-) three-connected nets.
Andrew Shamp1, James Hooper, Eva Zurek
1Department of Chemistry, State University of New York at Buffalo, Buffalo, New York 14260-3000, United States.
Inorganic Chemistry
|August 18, 2012
Summary
Stable cesium polyhydrides, including CsH3, form at moderate pressures. CsH3 exhibits multiple phases, some metallic and others insulating, depending on pressure and structure.
Area of Science:
- Materials Science
- High-Pressure Physics
- Computational Chemistry
Background:
- Cesium polyhydrides (CsH(n), n > 1) are compounds of interest for their potential unique properties under pressure.
- Previous studies have explored the phase diagrams of alkali metal hydrides, but the specific behavior of CsH(n) at high pressures requires further investigation.
Purpose of the Study:
- To investigate the stability and structural properties of cesium polyhydrides (CsH(n), n > 1) under high pressure.
- To identify the most stable stoichiometry and phases of cesium polyhydrides.
- To determine the electronic properties (metallic or insulating) of predicted CsH3 phases.
Main Methods:
- Employing evolutionary algorithms to predict stable structures of CsH(n) at pressures between 30 and 200 GPa.
- Utilizing screened hybrid density functional theory (DFT) calculations to assess mechanical stability and electronic band structures.
- Analyzing enthalpy of formation to identify the most stable CsH3 stoichiometry.
Main Results:
- Cesium polyhydrides are predicted to be stable at pressures as low as 2 GPa.
- CsH3 exhibits the lowest enthalpy of formation from CsH and H2 between 30 and 200 GPa, with five distinct, mechanically stable phases predicted.
- Two phases with hexagonal H3(–) nets become metallic below 100 GPa, while three phases with twisted H3(–) nets remain insulating up to 250 GPa.
Conclusions:
- CsH3 is a stable compound under high pressure, existing in multiple structural phases with varying electronic properties.
- The specific arrangement of H3(–) molecules within the crystal lattice dictates whether the material is metallic or insulating.
- The findings provide crucial insights into the high-pressure behavior of hydrogen-rich materials and potential for novel electronic properties.
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