Metal dichalcogenides are excellent solid lubricants due to their graphitic structure and weak inter-layer bonding, which combine to facilitate shear. One of the typical metal dichalcogenides is tungsten disulfide (WS₂), which can be either dispersed into liquid lubricants, like graphite, to reduce the friction and wear between moving surfaces; or used as a solid lubricant by itself. WS2 is an intrinsic solid lubricant and it functions effectively as a lubricant in air and inert gases as well as in high vacuum over a large temperature range. In the solid, the molecular units line up to form a hexagonal crystal structure in which the adjacent molecules along [001] direction interact through weak van der Waals forces. The unit cell includes two adjacent layers and thus has hexagonal symmetry with a 2H arrangement. As part of the Ph.D. thesis project of Emre Selvi, a CDAC group from Texas Tech including Yanzhang Ma, Resul Aksoy, Atila Ertas, and Allen White carried out high pressure synchrotron x-ray diffraction experiments to investigate the properties of WS₂ to 26 GPa at room temperature. By fitting the P-V data to its equation of state parameters, the bulk modulus was determined. The c-axis of the hexagonal structure is found to be much more compressible than the a-axis [Selvi, et al., J. Phys. Chem. Solids, 67, 2183-2186 (2006)].

Another disulfide, MoS₂, has a crystal structure and applications similar to those of WS₂. As part of his Ph.D. thesis project at Texas Tech, Resul Aksoy and his advisor and coauthors, Ma, Selvi, Ming C. Chyu, Ertas, and White investigated the high-pressure behavior of MoS₂, by synchrotron x-ray diffraction, to nearly 40 GPa at room temperature. The ratio of the compressibilities of the c-axis to the a-axis is approximately 3 at lower pressures (below 10 GPa). The ratio gradually decreases with increasing pressure with an apparent, phase transformation at high pressure and low temperature [Aksoy, et al., J. Phys. Chem. Solids, 67, 1914-1917 (2006)].