Bond length anomaly in TiB₂ at high pressure: first principles calculations

The effect of pressure on the electronic structure, Fermi surface, nature of bonding, elastic constants and phonon dispersion properties of TiB₂ have been studied by performing detailed ab—initio calculations. Plane wave pseudopotential method and the full potential linearized augmented plane wave method (FP-LAPW) have been employed for the computation. TiB₂ assumes a layered structure. Nevertheless, the dispersion corrected density functional approach brought out the fact that long ranged van der Waals interactions are negligible in this system and it is bound by strong inter layer coupling. The calculated optimized structure parameters and bulk modulus are in good agreement with the available theoretical and experimental values. Calculations carried out as a function of pressure show a decrease in structural parameters, bond lengths and an increase in elastic constants. TiB₂ structure is observed to be mechanically and dynamically stable up to 22 GPa from phonon dispersion calculations. Most interestingly the present computations efforts corroborate the experimentally observed bond length anomaly in TiB₂ at 12 GPa and attributes it to a redistribution of charges at that pressure. In addition the results of the computation at high pressure up to 22 GPa elucidates the fact that TiB₂ is a hard metallic material. (paper)