Synthesis and Characterization of K and Eu Binary Phosphides

The synthesis, structural characterization, and optical properties of the binary Zintl phases of α-EuP(3), β-EuP(3), EuP(2), and α-K(4)P(6) are reported in this study. These crystal structures demonstrate the versatility of P fragments with dimensionality varying from 0D (P(6) rings in α-K(4)P(6)) to 1D chains (EuP(2)) to 2D layers (both EuP(3)). EuP(2) is isostructural to previously reported SrP(2) and BaP(2) compounds. The thermal stabilities of the EuP(2) and both EuP(3) phases were determined using differential scanning calorimetry (DSC), with melting temperatures of 1086 K for the diphosphide and 1143 K for the triphosphides. Diffuse reflectance spectroscopy indicated that EuP(2) is an indirect semiconductor with a direct bandgap of 1.12(5) eV and a smaller indirect one, less than 1 eV. Both EuP(3) compounds had bandgaps smaller than 1 eV.