High-concentration Na doping of SrRuO3 and CaRuO3.

The Na-doped perovskite-structure ruthenates Sr(1-x)Na(x)RuO3 and Ca(1-y)Na(y)RuO3 were prepared by high-pressure synthesis, which enables us to go beyond the previously reported Na doping limits and substitute Na for over 50% of the Sr in SrRuO3 and the Ca in CaRuO3. Gradual and systematic changes in the crystal structures were observed, and the decreases in the Ru-O bond lengths confirmed the Na substitution at the A site caused hole doping to Ru(4+) at the B site. In contrast to what has been previously reported, Sr(1-x)Na(x)RuO3 showed metallic conductivity. Magnetic properties were influenced by the Na substitution, but no long-range antiferromagnetic behavior was observed in Ca(1-y)Na(y)RuO3.