X-ray crystal structure analysis and Ru valence of Ba₄Ru ₃O₁₀ single crystals

We present a single-crystalline x-ray diffraction study on Ba4Ru3O10 consisting of corner-shared Ru₃O₁₂ trimers. The crystal structure is redetermined from 78 to 300K across an antiferromagnetic transition at 105 K. The orthorhombic symmetry (Cmca, space group No. 64) is preserved at all temperatures measured. This structure presents exceptionally long Ru-O distances characterized by a significant distribution within the Ru ₃O₁₂ trimer. A bond valence sum calculation suggests that the charge disproportionation within the Ru₃O₁₂ trimer emerges even at room temperature, which we ascribe to molecular orbital formation in the Ru₃O₁₂ trimer, as supported by the results of recent theoretical calculations. On the basis of the analyzed crystal structure, the electronic states and the nature of the phase transition at 105K are discussed.