High-pressure equation of state for Nb with a helium-pressure medium: Powder x-ray diffraction experiments

Abstract

High-pressure powder x-ray diffraction experiments have been carried out on Nb at room temperature up to $134\phantom{\rule{0.3em}{0ex}}\mathrm{GPa}$ with a He-pressure medium and $145\phantom{\rule{0.3em}{0ex}}\mathrm{GPa}$ with an alcohol-water pressure medium. Nb remains in the bcc structure to the highest pressure investigated. The bulk modulus and its pressure derivative have been determined from the data with the He medium as ${B}_{0}=168(4)\phantom{\rule{0.3em}{0ex}}\mathrm{GPa}$ and ${B}_{0}^{\ensuremath{'}}=3.4(3)$. No anomaly is found in the equation of state of Nb to be connected with the electronic topological transitions, which were inferred from the anomalies in the superconducting transition temperature under pressure. The origin of the asymmetric broadening of the diffraction peaks is discussed.