Existence of carbonate clusters and its relationship with critical temperature in superconducting (Cu,C)Ba2Ca3Cu4Oy films

Abstract The nontoxic cuprate superconductor (Cu,C)Ba2Ca3Cu4Oy [(Cu,C)-1234] with critical temperature of about 117 K is supposed to have great potential for applications in the liquid nitrogen temperature region. Using pulsed laser deposition technique, we successfully obtain superconducting (Cu,C)-1234 films on LaAlO3 (001) substrates with different critical temperatures by tuning the flow rate of CO2 gas during the deposition. The existence of CO 3 2 − carbonate clusters in our (Cu,C)-1234 films is directly confirmed by the mid-infrared transmittance spectra measured on these films. Our results also reveal that the content of the CO 3 2 − carbonate clusters increases with the flow rate of CO2. The zero-resistance critical temperature (Tc0) of the films exhibits dome-like behaviour as the content of CO 3 2 − carbonate clusters increases. Our observations not only provide clear evidence for the existence of CO 3 2 − carbonate clusters in the films, but also testify that the content of CO 3 2 − carbonate clusters has considerable influence on the superconducting properties of the films.