# A new form of Ca 3 P 2 with a ring of Dirac nodes

## Author(s): Xie, Lilia S; Schoop, Leslie M; Seibel, Elizabeth M; Gibson, Quinn D; Xie, Weiwei; et al

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 Abstract: We report the synthesis and crystal structure of a new high-temperature form of Ca3P2. The crystal structure was determined through Rietveld refinements of synchrotron powder x-ray diffraction data. This form of Ca3P2 has a crystal structure of the hexagonal Mn5Si3 type, with a Ca ion deficiency compared to the ideal 5:3 stoichiometry. This yields a stable, charge-balanced compound of Ca2+ and P3− . We also report the observation of a secondary hydride phase, Ca5P3H, which again is a charge-balanced compound. The calculated band structure of Ca3P2 indicates that it is a three-dimensional Dirac semimetal with a highly unusual ring of Dirac nodes at the Fermi level. The Dirac states are protected against gap opening by a mirror plane in a manner analogous to what is seen for graphene. Publication Date: Aug-2015 Citation: Xie, Lilia S, Schoop, Leslie M, Seibel, Elizabeth M, Gibson, Quinn D, Xie, Weiwei, Cava, Robert J. (2015). A new form of Ca 3 P 2 with a ring of Dirac nodes. APL Materials, 3 (8), 083602 - 083602. doi:10.1063/1.4926545 DOI: doi:10.1063/1.4926545 EISSN: 2166-532X Pages: 083602 - 083602 Type of Material: Journal Article Journal/Proceeding Title: APL Materials Version: Final published version. This is an open access article.