Chalcogenides of the quasi-ternary system Tl2S-PbS-SiS2 were synthesized in the evacuated silica ampoules by the melting and annealing technique. Phase equilibria in the system was investigated by XRD method. Isothermal section of the system was studied, and two intermediate quaternary phases were discovered to exist (TI2PbSiS4, similar to TI2PbSi3S8). The quasi-binary section Tl2SiS3-PbS was investigated by DTA. Its phase diagram was constructed, and it was established that the equimolar compound melts incongruently at 818 K. The crystal structure of the quaternary compound Tl2PbSiS4 was determined by X-ray powder diffraction. It crystallizes in the monoclinic space group P2(1)/alpha with the unit-cell parameters alpha = 8.8141(4), b = 9.0150(5), c = 10.4383(5) angstrom, and beta (3 = 94.490(4)degrees (Tl2PbGeS4 structure type). Reliability factors calculated in the isotropic approximation were found to be R-I = 0.0564 and R-p = 0.1070. The Tl2PbSiS4 single crystal was tested with X-ray photoelectron spectroscopy. In particular, the XPS core level and valence-band spectra were recorded for pristine and Ar+-ion bombarded surfaces of Tl2PbSiS4. The Tl2PbSiS4 single crystal was found to be rather stable with respect to Ark(+)-ion irradiation. We have also measured the X-ray emission band depicting the energy distribution of mainly the S 3p states and compared it on a common energy scale with the XPS valence-band spectrum of the Tl2PbSiS4 crystal. The above comparison indicates that the S 3p states contribute substantively in the upper portion of the valence band of TI2PbSiS4, with their significant contributions in other portions of the valence band region. (C) 2017 Elsevier B.V. All rights reserved.