Growth and Characterization of a New Superconductor GaBa_2Ca_3Cu_4O_11+\delta

We successfully grow a new superconductor GaBa_2Ca_3Cu_4O_11+ \delta (Ga-1234) with a transition temperature of 113 K, using the Walker-type high-pressure synthesis apparatus. X-ray diffraction measurements on the powderized samples show a mixture of the Ga-1234 phase and the Ca_0.85CuO_2 phase, and the former is dominant. Under the scanning electron microscope, plate-like crystals of the Ga-based 1234 phase with shiny surfaces can be seen. The obtained local chemical compositions revealed by energy dispersion x-ray spectroscopy are very close to the stoichiometric values. On some sub-millimeter crystal-like samples of the 1234 phase, we obtain a full Meissner shielding volume. From the temperature-dependent magnetizations, we determine the irreversibility fields and find that the system exhibits a highly anisotropic behavior.