KCu7P3: A Two-Dimensional Noncentrosymmetric Metallic Pnictide.

We report a 2D material, KCu7P3, with a noncentrosymmetric structure (trigonal space group P31m, a = 6.9637(2) Å, c = 24.1338 (10) Å), which forms both from a molten potassium polyphosphide flux and from the elements. This phase consists of infinite [Cu7P3]- layers with hexagonal P sheets separated by K+ ions. The structure of the layers is unique but related to both Cu3P and the CaCu4P2 structure-types. Single-crystal refinement reveals extensive disorder within the Cu3P-like slabs. KCu7P3 is paramagnetic and exhibits a room temperature resistivity of ∼335 μΩ cm with a metal-like temperature dependence. The metallic character is supported by density functional theory electronic structure calculations. Hall and Seebeck effect measurements yield p-type behavior with a hole mobility of ∼15 cm2 V-1 s-1 at 300 K and a carrier concentration on the order of 1021 cm-3. KCu7P3 is chemically stable in ambient conditions, as well as in aqueous neutral and acidic solutions.