The transition--metal oxide CaCu3Ru4O12 with perovskite--type structure shows characteristic properties of an intermediate--valence system. The temperature--dependent susceptibility exhibits a broad maximum around 150−160 K. At this temperature, neutron powder diffraction reveals a small but significant volume change whereby the crystal structure is preserved. Moreover, the temperature--dependent resistivity changes its slope. NMR Knight shift measurements of Ru reveal a cross--over from high temperature paramagnetic behavior of localized moments to itinerant band states at low temperatures. Additional density--functional theory calculations can relate the structural anomaly with the d--electron number. The different experimental and calculational methods result in a mutually consistent description of CaCu3Ru4O12 as an intermediate--valent system in the classical sense of having low--energy charge fluctuations.
@article{arxiv.0909.4208,
title = {Intermediate-valence behavior of the transition-metal oxide CaCu$_3$Ru$_4$O$_{12}$},
author = {A. Krimmel and A. Günther and W. Kraetschmer and H. Dekinger and N. Büttgen and V. Eyert and A. Loidl and D. V. Sheptyakov and E. -W. Scheidt and W. Scherer},
journal= {arXiv preprint arXiv:0909.4208},
year = {2009}
}