On the compression behaviour of (Ti(0.5),V(0.5))(2)AlC and (Ti(0.5),Nb(0.5))(2)AlC to quasi-hydrostatic pressures above 50 GPa.

Using a synchrotron x-ray radiation source and a diamond anvil cell we measured the functional dependences of the lattice parameters of (Ti(0.5),V(0.5))(2)AlC and (Ti(0.5),Nb(0.5))(2)AlC to quasi-hydrostatic pressure of the order of 50 GPa. Like for other solids in this family of layered ternary carbides and nitrides, the bulk moduli (≈183 GPa) are high and no phase transformations were observed. The bulk moduli of the solid solution compositions were lower than those of the end members. The effect was much more dramatic when Ti replaced Nb in Nb(2)AlC than when it replaced V in V(2)AlC. In the former case the modulus drops by 13% from 209 GPa, with the softening coming almost exclusively from the c-axis. This somewhat surprising result is ascribed to the corrugation of the Ti-Nb planes in (Ti(0.5),Nb(0.5))(2)AlC. When Ti replaced V in V(2)AlC the drop in modulus was 8%.