Dissociation products and structures of solid H2S - Dr. Lin Wang
JANUARY 11, 2016
A record of highest critical temperature (Tc) of about 200 K — a temperature that actually exists on Earth’s surface, reported in H2S has lit a fire in superconductivity. This major breakthrough in superconductivity suggest that so high Tc is most likely due to the decomposition product, H3S, which was predicted to have the comparative value in Tc at high pressure. These proposals bring the decompositions conducts of H2S to a new hot research topic. New study including Lin Wang, Yanwei Huang and Wentao Li, scientists from HPSTAR, utalizing experimental and theoretical simulations to probe decompositions of compressed H2S and possible stable structures, find that H4S3 is the major component of the dissociation products while there is just a small fraction of H3S.
For many years it was believed that superconductivity is just limited to ultra-low temperatures. But 1986, a Tc of 133 K was discovered in layered copper oxides (cuprates). This breakthrough driven scientists to discover even higher, ie., room temperature conventional superconductivity.
At first, people give attention to hydrogen, which provides a strong electron-phonon interaction. A high value of 300-500 K for Tc is estimated in atomic hydrogen, however, even metallic hydrogen hasn’t been experimentally confirmed since the first predication 80 years ago. So scientists are trying to find high-Tc superconducting in hydrogen dominated materials.
Thanks to the help from theorectical predications, H2S was predicted to be superconductor at ~100 gigapascals with a high Tc of ~80 K. And recently, a high Tc of ~200 K was reported in hydrogen rich compound, sulfur hydride at ~90 gigapascals. This high Tc superconductivity is supposedly due to H3S from decomposed H2S at high pressure. The decomposition products of compressed H2S thus attract considerable interest.
In this study, utilizing theoretical calculations and experiments, scientists clarifies the possible decomposition products of compressed H2S and their structures. Using diamond anvil cell technique, H2S was compressed up to ~ 140 GPa. There is just a small fraction of H3S while more H4S3 in the decomposed products, and H4S3 is also predicted to be thermodynamically stable within a large pressure range from DFT calculations. Also from DFT calculations, H4S3 is predicted to have a low Tc of below 2K, and H2S is mainly responsible for the observed superconductivity below 160 gigapascals in samples prepared at low temperature (<100 K).
Caption: Compressed H2S up to about 140 GPa.
The study is published by recent Phy. Rev. B (Rapid communications)
“We find that kinetics plays an important role in determining the experimentally observed H-S structures”, said Lin Wang, one co-author of this work and staff scientist at HPSATR.