  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.
  %In spite of the polycrystalline bulk samples, we obtained the higher
residual resistivity ratios (10-12).
  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 upper critical magnetic field is estimated to be about 35 T at low
temperatures from the resistive transition data using the
Werthamer-Helfand-Hohenberg 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 homogeneous distributions of the superconducting
grains and improved weak links between their superconducting grains in the
present synthesis process.
