Superconductivity: Effect of lanthanum and cerium substitution on the superconducting state of Ba0.6K0.4BiO3

The search for room-temperature superconductivity has been a major focus of condensed matter physics research for the last 60 years. The highest critical temperature known today for a superconductor at ambient pressure is 133 K; this is almost half-way to room temperature (290 K). Many high-temperature superconductors belong to a family of copper-oxide-based compounds called cuprates. The superconductor Ba0.6K0.4BiO3, with a critical temperature of 30 K, is one of the highest-temperature superconductors that is not a cuprate. Research has shown that its superconducting state shares many similarities with those of the cuprates. In this project, we studied the superconducting properties of Ba0.6K0.4BiO3 by determining the impact of chemical substitution with lanthanum and cerium (Ba0.6-y LayK0.4BiO3 and Ba0.6-zCezK0.4BiO3). Previous studies have investigated the effect of lanthanum substitution on the superconducting state of Ba0.6K0.4BiO3. We focused primarily on the effect of introducing magnetic moments through cerium substitution on superconductivity. Samples were synthesized at relatively low temperature (260 °C) using the molten salt technique. The phase purity of samples was evaluated via measurements of x-ray diffraction. Magnetic susceptibility measurements as a function of temperature were performed to characterize the superconducting states of our samples. A comparison between the results for the cerium- and lanthanum-doped samples allows us to isolate and study the effect of magnetic moments on superconductivity in Ba0.6K0.4BiO3