Single-crystal structure ofHoBaCo4O7at ambient conditions, at low temperature, and at high pressure

Abstract

We show that the correct space group of ${\text{HoBaCo}}_{4}{\text{O}}_{7}$ at ambient conditions is $P{6}_{3}mc$ and that no temperature-induced or pressure-induced structural phase transition occurs down to 100 K or up to 9 GPa. The compressibility of ${\text{HoBaCo}}_{4}{\text{O}}_{7}$ is mainly determined by a combination of bond compression and changes in the three-membered and six-membered rings of the kagom\'e layers. ${\text{HoBaCo}}_{4}{\text{O}}_{7}$ is more compressible than structurally related compounds due to the comparatively compressible Co-O bonds. The structural analysis allows us to propose an atomistic model for the extremely high oxygen incorporation capability of ${\text{HoBaCo}}_{4}{\text{O}}_{7}$.