Na-based osmium oxide pyrochlore was synthesized for the first time by an ion-exchange method. KOs2O6 was used as a host compound. Elelectron probe micro-analysis, synchrotron x-ray diffraction analysis, and thermo-gravimetric analysis confirmed its structure not as the beta-type but as the defect-type pyrochlore. The composition was identified as Na1.4Os2O6.H2O. Electrical resistivity, heat capacity, and magnetization measurements of the polycrystalline Na1.4Os2O6.H2O clarified absence of superconductivity above 2 K, being in contrast to what were found for the beta-pyrochlore AOs2O6 (A = Cs, Rb, K). Sommerfeld coefficient of 22 mJ K-2 mol-1 of Na1.4Os2O6.H2O was smallest among those of AOs2O6. A magnetic anomaly at ~57 K and possible associated magnetoresistance (+3.7 % at 2 K in 70 kOe) were found.
@article{arxiv.0808.2331,
title = {Magnetic and charge transport properties of the Na-based Os oxide pyrochlore},
author = {Y. G. Shi and A. A. Belik and M. Tachibana and M. Tanaka and Y. Katsuya and K. Kobayashi and K. Yamaura and E. Takayama-Muromachi},
journal= {arXiv preprint arXiv:0808.2331},
year = {2009}
}