The high-pressure structural behavior of the fluoroperovskite $\mathrm{K}\mathrm{Mg}{\mathrm{F}}_3$ is investigated by theory and experiment. Density functional calculations were performed within the local density approximation and the generalized gradient approximation for exchange and correlation effects, as implemented within the full-potential linear muffin-tin orbital method. In situ high-pressure powder x-ray diffraction experiments were performed up to a maximum pressure of $40\mathrm{GPa}$ using synchrotron radiation. We find that the cubic $Pm\overline{3}m$ crystal symmetry persists throughout the pressure range studied. The calculated ground state properties—the equilibrium lattice constant, bulk modulus, and elastic constants—are in good agreement with experimental results. By analyzing the ratio between the bulk and shear moduli, we conclude that $\mathrm{K}\mathrm{Mg}{\mathrm{F}}_3$ is brittle in nature. Under ambient conditions, $\mathrm{K}\mathrm{Mg}{\mathrm{F}}_3$ is found to be an indirect gap insulator, with the gap increasing under pressure.

• Received 21 March 2007

DOI:https://doi.org/10.1103/PhysRevB.76.014107