Quasibinary section of AgGaSe<sub>2</sub>-PbS
In recent years, researchers in optoelectronics have been interested in investigating the compound A<sup>I</sup>B<sup>III</sup>C<sup>VI</sup>2 (A<sup>I</sup>-Cu, Ag; B<sup>III</sup>-Ga, In ; C<sup>VI</sup>-S, Se) with a chalcopyrite structure and the solid solutions. This attention is mainly due to the promising use of copper and silver-containing representatives of these compounds (CuInS<sub>2</sub>, CuInSe<sub>2</sub>) with p-type conductivity as an absorbing layer of thinfilm solar cells. The ligatures (AgGaSe<sub>2</sub>, PbSe) were synthesized in evacuated quartz ampoules from elements taken in appropriate ratios at 1150 and 1370 Kfor 3 h, followed by air cooling. Pb, Ag, Ga, and Se of high purity with a basic substance content of at least 99.999% were used as starting materials. The samples were annealed at 600 K for 300-350 h. Samples of the AgGaSe<sub>2</sub>-PbSe section were synthesized at 1150-1370 K. The samples obtained were annealed at 600 K for 350 h. The XRD, DTA, and metallographic analysis, microhardness and density measurements were used to study phase equilibria in the AgGaSe<sub>2</sub>-PbSe section of the Ag<sub>2</sub>Se-Ga<sub>2</sub>Se<sub>3</sub>-PbSe quasi-ternary system. The T-x phase diagram of the system was constructed, and the presence of a quaternary compound of the composition AgPb<sub>2</sub>GaSe<sub>4</sub>, formed at 1110 K by the peritectic reaction, was established. The conditions of formation were determined, and the physicochemical properties of the AgPb<sub>2</sub>GaSe<sub>4</sub> compound were studied. It was found that the AgPb<sub>2</sub>GaSe<sub>4</sub> compound crystallized in the orthorhombic system with the crystal lattice parameters a = 8.5201, b = 7.2311, c = 6.9203 Å, Sp.gr. Pmn21. It was shown that the solubility based on AgGaSе<sub>2</sub> at room temperature reached 12 mol.% (β-phase), and on the basis of PbSe, 8 mol.%AgGaSe<sub>2</sub>.