Synthesis and structural characterization of the ternary Zintl phases AE _3Al _2Pn _4 and AE _3Ga _2Pn _4 (AE=Ca, Sr, Ba, Eu; Pn=P, As)

摘要

Ten new ternary phosphides and arsenides with empirical formulae AE _3Al _2Pn _4 and AE _3Ga _2Pn _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 - Ca _3Al _2P _4, Sr _3Al _2As _4, Eu _3Al _2P _4, Eu _3Al _2As _4, Ca _3Ga _2P _4, Sr _3Ga _2P _4, Sr _3Ga _2As _4, and Eu _3Ga _2As _4 crystallize with the Ca _3Al _2As _4 structure type (space group C2/c, Z=4); Ba _3Al _2P _4 and Ba _3Al _2As _4 adopt the Na _3Fe _2S _4 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 [TrP ~(n2)]32 layers in the phases with the Ca _3Al _2As _4 structure, and [TrP ~(n2)]31 chains in Ba _3Al _2P _4 and Ba _3Al _2As _4 with the Na _3Fe _2S _4 structure type. The valence electron count for all of these compounds follows the ZintlKlemm rules. Electronic band structure calculations confirm them to be semiconductors.