THE Pr3Ga1,67Se7 – Pr3Ge1,25Se7 SYSTEM

Abstract

Interaction of the components in Pr 3 Ga 1,67 Se 7 – Pr 3 Ge 1,25 Se 7 system and crystal structure of the quaternary phase Pr 3 GaGe 0,5 Se 7 have been investigated using X-ray phase analysis. The alloys were synthesized from elementary substances of at least 99.99 wt. % purity in quartz containers in an MP-30 programmable electric muffle furnace. Containers were evacuated to a residual pressure of 10-2 Pa and soldered in oxygen-gas burner flame. The alloys were synthesized by: 1) heating the mixture to 870 K at the rate of 30 K/h; 2) exposure for 100 h; 3) heating to 1370 K at the rate of 12 K/h; 4) exposure for 2 h; 5) cooling to 770 K at the rate of 12 K/h; 6) homogenizing annealing for 500 h. After reaching the equilibrium state, the synthesized alloys were quenched into room-temperature water. The diffraction patterns for X-ray phase analysis were recorded at a DRON 4-13 diffractometer for 2Q range of 10-80° (CuKα radiation, scan step 0.05°, 4 s exposure in each point). Data processing and the determination of the crystal structure utilized WinCSD software package. A continuous solid solution series is formed in the Pr 3 Ga 1,67 Se 7 – Pr 3 Ge 1,25 Se 7 system. At 770 K, the parameter a of the hexagonal cell varies within the solid solution from 1,0354(3) nm to 1,0620(3) nm. The parameter c varies from 0,6391(2) nm to 0,6057(1) nm, and the cell volume from 0,59336 nm 3 to 0,59163 nm 3 . The Pr atoms are centered on trigonal prisms with one additional atom. These prisms are formed by Se atoms. The atoms of the statistical mixture M1 (0,333 Ga + 0,167 Ge) are located practically in the centers of the octahedra of Se atoms ([M16Se1]). Atoms M2 (0,667 Ga + 0,333 Ge) are located in tetrahedraof Se atoms ([M 23 Se 21 Se 3 ]).