Normal state properties and oxygen isotope effect of (Ba,K)BiO3

Abstract

Abstract Experimental results of Hall effect, thermoelectric power and magnetic susceptibility of the Cu-free high-Tc oxides, (Ba,K)BiO3 are presented. It is shown that the electronic nature of (Ba,K)BiO3 is quite different from those of high-Tc oxides with CuO2 planes. One of the remarkable differences between the Bi and Cu systems is that the charge carriers of the former are electrons with small effective mass, while the charge carriers of the latter are holes with large effective mass. We also measured the effect of oxygen isotope substitution on its Tc, where we first synthesized BaO2, KO2 and Bi2O3 by using 16O and 18O in parallel , and then the superconducting oxide (Ba,K)BiO3 was synthesized from these oxides, which guaranteed the complete substitution of 16O by 18O. A large oxygen isotope effect (α≅0.35) suggests that the usual phonon mediated pairing mechanism is working in the present system.