Enhanced superconducting properties of double-chain based superconductor Pr$_{2}$Ba$_{4}$Cu$_{7}$O$_{15-\delta}$ synthesized by citrate pyrolysis technique.

We report the enhanced superconducting properties of double-chain based superconductor Pr$_{2}$Ba$_{4}$Cu$_{7}$O$_{15-\delta}$ synthesized by the citrate pyrolysis technique. The reduction heat treatment in vacuum results in the appearance of superconducting state with $T_\mathrm{c}$=22-24 K, accompanied by the higher residual resistivity ratios. The superconducting volume fractions are estimated from the ZFC data to be 50$\sim55\%$, indicating the bulk superconductivity. We evaluate from the magneto-transport data the temperature dependence of the superconducting critical field, to establish the superconducting phase diagram. The critical magnetic field is estimated to be about 26 T at low temperatures from the resistive transition data using the empiric formula. The Hall coefficient $R_{H}$ of the 48-h-reduced superconducting sample is determined to be -0.5$\times10^{-3}$ cm$^{3}$/C at 30 K, suggesting higher electron concentration. These findings have a close relationship with the enhanced superconducting properties, leading to the phase diagram of the present samples.