The effect of high pressures, up to 40 GPa, on the crystal structure and lattice dynamics of ${\mathrm{AlB}}_2$ was studied by synchrotron x-ray powder diffraction, Raman spectroscopy, and first-principles calculations. There are no indications for a pressure-induced structural phase transition. The Raman spectra of the metallic sample exhibit a well-defined peak near $980{\mathrm{cm}}^{-1}$ at 0 GPa, which can be attributed to the Raman-active $E_{2g}$ zone-center phonon. Al deficiency of $\sim 11\%$ in ${\mathrm{AlB}}_2,$ as indicated by the x-ray data, changes qualitatively the electronic structure, and there are indications that it may have a sizable effect on the pressure dependence of the $E_{2g}$ phonon frequency. Similar changes of the pressure dependence of phonon frequencies, caused by nonstoichiometry, are proposed as an explanation for the unusually large variation of the pressure dependence of $T_c$ for different samples of ${\mathrm{MgB}}_2.$

• Received 5 June 2002

DOI:https://doi.org/10.1103/PhysRevB.66.134101