Materials by design at high pressures

Abstract

Pressure, a fundamental thermodynamic variable, can generate two essential effects on materials. First, pressure can create new high-pressure phases via modification of the potential energy surface. Second, pressure can produce new compounds with unconventional stoichiometries via modification of the compositional landscape. These new phases or compounds often exhibit exotic physical and chemical properties that are inaccessible at ambient pressure. Recent studies have established a broad scope for developing materials with specific desired properties under high pressure. Crystal structure prediction methods and first-principles calculations can be used to design materials and thus guide subsequent synthesis plans prior to any experimental work. A key example is the recent theory-initiated discovery of the record-breaking high-temperature superhydride superconductors H₃S and LaH₁₀ with critical temperatures of 200 K and 260 K, respectively. This work summarizes and discusses recent progress in the theory-oriented discovery of new materials under high pressure, including hydrogen-rich superconductors, high-energy-density materials, inorganic electrides, and noble gas compounds. The discovery of the considered compounds involved substantial theoretical contributions. We address future challenges facing the design of materials at high pressure and provide perspectives on research directions with significant potential for future discoveries.

Fig. 1. (a) Comparison of the calculated and measured T_c for H₂S pressurized at low temperature. Insets show two predicted structures. (b) Comparison of the calculated and measured T_c for H₂S pressurized at high temperature. The inset shows the predicted structure.

Fig. 2. Computed (light blue) and measured (dark blue) T_c of covalent hydrides since 2014.

Fig. 3. (a) Measured resistance as a function of temperature of LaH₁₀ at 151 GPa. The inset presents the predicted clathrate structure. (b–d) Three typical clathrate structures of superhydrides formed at high pressures.

Fig. 4. (a) Summary of the computed (green) and measured (blue) T_c of several typical superconducting superhydrides. (b) Proportion of H-s electron states at the Fermi level for selected superconducting superhydrides.

Fig. 5. Crystal structures of (a) alpha-N, (b) cg-N, (c) BP-N, (d) Pba2-N, (e) I-43m-N, and (f) P4₂bc-N.

Fig. 6. Polymerization of nitrogen in alkali metal azides at high pressure.

Fig. 7. Three-dimensional electron localization function maps of (a) hP4-Na at 200 GPa, (b) anti-CdCl₂-type Ca₂N at ambient pressure, and (c) I4̄2d Ca₂N at 20 GPa to show electron localization in the lattice interstices.

Fig. 8. Predicted and confirmed crystal structures of (a) XeFe₃, (b) XeNi₃, (c) Xe₃O₂, and (d) Na₂He.