The p, T, x diagram of the Sn-S system was determined especially in the region of the compound SnS. The pressure of S2 in equilibrium with SnS and a liquid phase was found to extend over several decades up to 25-mm Hg at the ``Sn-rich'' side, whereas at the ``S-rich'' side the S2 pressures in equilibrium with solid SnS and a liquid phase lie between 25-mm Hg and 100-mm Hg. It was shown that the existence region of solid SnS very probably lies entirely at the excess sulfur side. The hole mobility in a plane perpendicular to the c axis, ≈90 cm2/v sec at room temperature, was proportional to T−2,2 for higher temperatures. The mobility in the direction of the c axis was about five times smaller. Reversible annealing effects were found for temperatures above 200°C which could be explained by assuming association of neutral Sn vacancies. Absorption measurements showed that the edge absorption is due to indirect transitions. The bandgap was 1.08 ev at 300°K and 1.115 ev at 77°K. Interband transitions in the valence band were also found. The effective charge of the atoms (e*=0.7e0) and the effective masses of the holes in the three principal crystal directions (ma*=mb*=0.20m0; mc*≈m0) were determined from reflection measurements in the infrared. From these values and the value for the density of states mass obtained by means of the Seebeck effect (md*≥0.95m0), the number of equivalent maxima of the valence band was found to be at least four.

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Electronic band-structure calculations are presented for the ferromagnetic compounds CrTe, Cr,Te, and Cr,Te,. In these compounds the Cr 3d-Te 5p covalency and the Cr 3dZz-Cr 3d12 overlap along the c axis are the most important interactions. The magnetic polarisation o f T e is parallel to the Cr local moment in CrTe, antiparallel to it in Cr,Te, and about zero in Cr,Te,. Measurementsofelectronic transport properties (resistivity. Halleffect andthermo-electricpower) andmagneticpropertiesofCr,_,)Te (6 = O.l)andCr,..,Te,(x = 0.2) indicate that these chromium tellurides are p-type metals, with strong interaction between the holes in the Te 5p band and the Cr magnetic moments. In the literature the variation of the magnetic properties of Cr? ?Te, near T, = 100 K has been attributed to a change from a canted antiferromagnetic to a collinear ferromagnetic structure. However, our Hall-effect measurements indicate that the spin structure is not collinear ferromagnetic above T,.

Ab initio band-structure calculations were performed for bulk, single slab, and thin films of TiX 2 ͑XϭS, Se͒ using the localized spherical wave method. According to these calculations, bulk TiS 2 and TiSe 2 are semimetallic. The calculations show that TiS 2 thin films are semiconductors, but thin films of TiSe 2 are semimetallic. The indirect gap for single slab TiS 2 is about 1.0 eV, and the gap becomes smaller with increasing number of layers. When the number of layers increases to 11, the TiS 2 thin films are semimetallic. All but the surface layers are found to be electrically neutral. The density of states as a function of the energy for the surface layer is different from that of the bulk. The Madelung energy of the Ti atoms on the surface is about 0.35 eV lower than that for the Ti atoms in the bulk. The calculations are compared with photoemission spectra, reported in the literature. ͓S0163-1829͑97͒05532-X͔