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Title: Metallicity of Ca2Cu6P5 with single and double copper-pnictide layers

Here, we report thermodynamic and transport properties, and also theoretical calculations, for Cu-based compound Ca2Cu6P5 and compare with CaCu2-dP2. Both materials have layers of edge-sharing copper pnictide tetrahedral CuP4, similar to Fe–As and Fe–Se layers (with FeAs4, FeSe4) in the iron-based superconductors. Despite the presence of this similar transition-metal pnictide layer, we find that both Ca2Cu6P5 and CaCu2-δP2 have temperature-independent magnetic susceptibility and show metallic behavior with no evidence of either magnetic ordering or superconductivity down to 1.8 K CaCu2-δP2 is slightly off-stoichiometric, with δ = 0.14. Theoretical calculations suggest that unlike Fe 3d-based magnetic materials with a large density of states (DOS) at the Fermi surface, Cu have comparatively low DOS, with the majority of the 3d spectral weight located well below Fermi level. The room-temperature resistivity value of Ca2Cu6P5 is only 9 μΩ-cm, due to a substantial plasma frequency and an inferred electron-phonon coupling λ of 0.073 (significantly smaller than that of metallic Cu). Also, microscopy result shows that Cu–Cu distance along the c-axis within the double layers can be very short (2.5 Å), even shorter than metallic elemental copper bond (2.56 Å). The value of dρ/dT for CaCu2-δP2 at 300 K is approximately three times larger thanmore » in Ca2Cu6P5, which suggests the likelihood of stronger electron-phonon coupling. This study shows that the details of Cu-P layers and bonding are important for their transport characteristics. In addition, it emphasizes the remarkable character of the DOS of ‘122’ iron-based materials, despite much structural similarities.« less
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  1. Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States)
  2. Univ. of Alabama at Birmingham, Birmingham, AL (United States)
Publication Date:
OSTI Identifier:
Grant/Contract Number:
Accepted Manuscript
Journal Name:
Journal of Alloys and Compounds
Additional Journal Information:
Journal Volume: 671; Journal Issue: C; Journal ID: ISSN 0925-8388
Research Org:
Univ. of Alabama at Birmingham, Birmingham, AL (United States)
Sponsoring Org:
USDOE National Nuclear Security Administration (NNSA)
Country of Publication:
United States
36 MATERIALS SCIENCE copper pnictide; thermal conductivity; superconductivity