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Synthesis of hafnium superhydrides at megabar pressures

Weizhao Cai1,2,*,†, Ying Sun3,*, Vasily S. Minkov2,*, Rachel Husband4, Stella Chariton5, Vitali B. Prakapenka5, Yanming Ma6,7,3,‡, and Mikhail I. Eremets2,§

  • *These authors contributed equally to this work.
  • †Contact author: wzhcai@uestc.edu.cn
  • ‡Contact author: mym@jlu.edu.cn
  • §Deceased.
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Phys. Rev. B 113, 224105 – Published 5 June, 2026

DOI: https://doi.org/10.1103/bjpf-6bt8

Abstract

Recent theories have predicted the existence of another class of hafnium superhydride P63/mmc−HfH10 with a two-dimensional layered structure and remarkable high-Tc around 213–234 K at 250 GPa. Its structure contains a planar pentagraphenelike hydrogen sublattice, which does not resemble the discovered high-Tc superconductors of covalent-bonded hydrogen structure of H3S and clathrate-type structure of LaH10. Here, we present the synthesis of hafnium superhydrides by the direct chemical reaction of Hf and H2 or with ammonia borane as the hydrogen source in laser-heated diamond anvil cells ranging from 200 to 302 GPa. Synchrotron x-ray diffraction data reveal the presence of previously predicted Pm3¯n−HfH3, Fddd-HfH4, and C2/m-HfH14 phases, and a unique triclinic phase P1¯−HfH10.5 was identified. Unfortunately, no existence of the P63/mmc−HfH10 phase was detected in the studied pressure range. Electrical resistance measurements demonstrate the synthesized products exhibiting good metallic character and absence of superconductivity down to ∼80 K. Theoretical calculations reveal the presence of the atomic H and H2 molecular units within the structure of P1¯−HfH10.5, which is mainly responsible for the low superconducting temperature.

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Phys. Rev. B 113, 224105– Published 5 June, 2026
  • Received 12 December 2022
  • Revised 7 May 2026
  • Accepted 12 May 2026
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