Soft‐chemistry synthesis of Ba 2 Ca 2 Cu 3 O x precursor and characterization of high‐T c Hg 0.8 Pb 0.2 Ba 2 Ca 2 Cu 3 O 8+  superconductor /T. BRYLEWSKI a,* , K. PRZYBYLSKI a , A. MORAWSKI b , D. GAJDA c , T. CETNER b , J. CHMIST d - BRYLEWSKI,T.