Synthesis and structural characterization of the ternary Zintl phases AE3Al2Pn4 and AE3Ga2Pn4 (AE=Ca, Sr, Ba, Eu; Pn=P, As)

Ten new ternary phosphides and arsenides with empirical formulae AE 3Al2Pn 4 and AE 3Ga2Pn 4 (AE =Ca, Sr, Ba, Eu; Pn =P, As) have been synthesized using molten Ga, Al, and Pb fluxes. They have been structurally characterized by single-crystal and powder X-ray diffraction to form with two different structures—Ca3Al2P4, Sr3Al2As4, Eu3Al2P4, Eu3Al2As4, Ca3Ga2P4, Sr3Ga2P4, Sr3Ga2As4, and Eu3Ga2As4 crystallize with the Ca3Al2As4 structure type (space group C 2/c , Z =4); Ba3Al2P4 and Ba3Al2As4 adopt the Na3Fe2S4 structure type (space group Pnma , Z =4). The polyanions in both structures are made up of TrPn 4 tetrahedra, which share common corners and edges to form View the MathML source[TrPn2]3–∞2 layers in the phases with the Ca3Al2As4 structure, and View the MathML source[TrPn2]3–∞1 chains in Ba3Al2P4 and Ba3Al2As4 with the Na3Fe2S4 structure type. The valence electron count for all of these compounds follows the Zintl–Klemm rules. Electronic band structure calculations confirm them to be semiconductors.