L Journal of Alloys and Compounds 336 (2002) 213–217 www.elsevier.com / locate / jallcom The Ag S–HgS–GeS system at 670 K and the crystal structure of the 2 2 Ag HgGeS compound 2 4 a, b a a * O.V. Parasyuk , L.D. Gulay , L.V. Piskach , O.P. Gagalovska a Department of General and Inorganic Chemistry, Volyn State University, Voli Ave 13, 43025 Lutsk, Ukraine b ¨ ¨ ¨ Institute f ur Physikalische Chemie, Universitat Wien, Wahringerstraße 42, A-1090 Wien, Austria Received 13 August 2001; accepted 10 October 2001 Abstract The isothermal section of the quasi-ternary Ag S–HgS–GeS system at 670 K has been constructed using results of X-ray powder 2 2 diffraction phase analysis and metallography. The existence of the Ag HgGeS and Ag Hg GeS compounds was confirmed and two 2 4 6 0.82 5.82 new quaternary Ag Hg GeS and |Ag HgGe S compounds were found. The crystal structure of the Ag HgGeS compound was 2 3 6 4 2 7 2 4 investigated using X-ray powder diffraction. This phase crystallizes in the wurtzite–stannite structure (space group Pmn2 ) with the 1 lattice parameters a 50.80247(4), b 50.68684(3) and c 50.65955(4) nm. The atomic parameters are refined in the anisotropic approximation to R 5 0.0748. The quaternary Ag Hg GeS compound crystallizes in the tetragonal structure ( a 51.4619(3) and I 2 3 6 c 52.0796(5) nm). The Ag Hg GeS phase (space group P2 3, a 5 1.05547 nm) has the homogeneity range in the Ag GeS – 6 0.82 5.82 1 8 6 Hg GeS section at 22–31 mol.% of Hg GeS . The structure of the |Ag HgGe S compound is under investigation. The constructed 4 6 4 6 4 2 7 phase diagram of the quasi-binary Ag S–HgS system has the eutectic type.  2002 Elsevier Science B.V. All rights reserved. 2 Keywords: Semiconductors; Crystal structure; X-ray diffraction; Phase diagram 1. Introduction preparation conditions for which we need to know the equilibrium diagram. The possible formation of the quaternary phases with The phase diagram of the Ag S–GeS system has been 2 2 semiconductor properties in the Ag S–HgS–GeS system studied several times [6–15]. The results of these works 2 2 was the reason for the investigation of this system. The prove the formation of the Ag GeS compound whereas 8 6 crystal structure of the Ag HgGeS compound has been the number and compositions of the compounds in the 2 4 described as a wurtzite–stannite structure (space group Ag GeS –GeS part of the diagram differ in different 8 6 2 Pmn2, a 5 0.8008, b 5 0.6871 and c 5 0.6593 nm) by works. The phase diagram of the Ag S–GeS section in 1 2 2 Haeuseler and Himmrich [1]. Recently, we have reported the interval of 0–50 mol.% of GeS was constructed in 2 on results of the crystal structure determination of a new Ref. [6]. The formation of the following compounds was quaternary Ag Hg GeS phase [2], which was found established: Ag GeS , Ag Ge S and Ag Ge S . The 6 0.82 5.82 8 6 6 2 7 8 3 10 in this system. The Ag Hg GeS compound crys- Ag GeS , Ag Ge S compounds melt congruently at 1223 6 0.82 5.82 8 6 6 2 7 tallizes in its own structure type (space group P2 3, a 5 and 958 K, respectively. The synthesized argyrodite 1 1.05547 nm). The possible formation of large glass-form- (Ag GeS ) exhibits the polymorphous transformation at 8 6 ing regions is another aspect which stimulated our interest 1093 K. Gorochov [7] has confirmed the existence of the to investigate this system. The glass-forming regions in the Ag GeS compound, displaying congruent melting at 1228 8 6 quasi-binary systems Ag S–GeS [3,4] and GeS –HgS [5] K and a phase transition at 493 K. The crystal structure of 2 2 2 are known. The considerable vapor pressure of binary the high-temperature modification of this compound was mercury and germanium sulphides makes it difficult for described as face-centered cubic ( a 51.070 nm) [7]. The obtaining alloys in glassy state. That is why we elaborated crystal structure of the low-temperature modification has been determined by Eulenberger [8] (space group Pna2, 1 a 5 1.5149, b 5 0.7476, c 5 1.0589 nm). Moh [9] has found only the existence of the Ag GeS compound during *Corresponding author. 8 6 E-mail address: oleg@lab.univer.lutsk.ua (O.V. Parasyuk). the investigation of the isothermal section of the Ag–Ge–S 0925-8388 / 02 / $ – see front matter  2002 Elsevier Science B.V. All rights reserved. PII: S0925-8388(01)01904-1