Pressure dependences of the elastic constants of single-crystalTi2O3at 296 K

We have measured the transit times of ultrasonic waves in ${\mathrm{Ti}}_2$ ${\mathrm{O}}_3$ at 296 K using hydrostatic pressures up to 4 kbar. From them we deduce the pressure dependences of the elastic constants. Most modes stiffen with increasing pressure. However, the quasishear mode propagating in the mirror plane 45° from the [001] axis is found to soften with increasing pressure. The softening is explained in terms of an intrinsic instability of a cation sublattice. Comparisons are made with elastic constants of ${\mathrm{Al}}_2$ ${\mathrm{O}}_3$ and ${\mathrm{V}}_2$ ${\mathrm{O}}_3$ at 1 bar and with the pressure dependences of the elastic constants of ${\mathrm{Al}}_2$ ${\mathrm{O}}_3$. It is inferred that electrons in $3d$ states contribute significantly to the elastic behavior of ${\mathrm{Ti}}_2$ ${\mathrm{O}}_3$.