Abstract:
The electrical conductivity (for T=16 to 300K) and magnetic susceptibility (for T=77 to 300K) of BaRuO3, CaRuO3 and SrRuO3 were measured. Samples with the nominal composition KxBa1-x RuO3 and LaxBa1-xRuO3 (x=.1,.2,.3,.4) were also prepared and the conductivity and susceptibility measured. To measure the susceptibility it was first necessary to build a magnetic susceptometer, an inductive design was developed, tested and found to be accurate to ±7x10-7emu.
It was found that all the samples were good conductors with room temperature resistivities of order ~ 1mΩ cm. BaRuO3 showed a semimetallic behaviour as the temperature decreased. The substituted compounds KxBa1-xRuO3 were found to have adopted the structure of the high temperature form of BaMnO3 which has a hexagonal unit cell consisting of 4 octahedrally coordinated Mn layers. The room temperature conductivity of these materials is similar in magnitude to that of BaRuO3 but the temperature dependence is metallic. Their susceptibility remains small and paramagnetic as in BaRuO3. It was found that the compounds LaxBa1-xRuO3 could not be prepared as single phase products. The susceptibility of BaRuO3 had been previously measured and the susceptibility and resistivity of SrRuO3 and CaRuO3 had also been previously measured. The results obtained in this project indicated that SrRuO3 and CaRuO3 were both metallic conductors with SrRuO3 ferromagnetic, Tc=150±10K, and CaRuO3 appearing to be a Curie-Weiss paramagnet in the temperature range covered. These results agreed with those that had been previously published.
The metallic versus nonmetallic character of KxBa1-xRuO3 (for x>0) and BaRuO3 was interrelated on the basis of the structure transition, from the 9 layered form of BaRuO3 to the 4 layered form of KxBa1-xRuO3. The very low susceptibility in BaRuO3 and KxBa1-xRuO3 is argued to be due to antiferromagnetic coupling.
