An Investigation of the Compressibility of LaB₆and EuB₆Using a High Pressure X-Ray Power Diffraction Technique

Abstract

The compressibilities of LaB6 and EuB6 have been determined using a high pressure X-ray powder diffraction technique. The compressibilities were found to be (0.58 ± 0.03) × 10-11 Pa-1 and (0.60 ± 0.03) × 10-11 Pa-1, respectively. No discontinuity has been found in the relative volume change vs. pressure curve of EuB6, which is semiconducting with a small band gap. This indicates that an overlap between the conduction band and the valence band does not occur within the pressure range examined (0-8 GPa). Furthermore, considering both the low compressibility of EuB6 and the large energy difference between the 4f7 level and the bottom of the conduction band (∼ 1 eV), an electronic transition Eu2+ → Eu3+ + e- seems unlikely even at very high pressures.