On synthesis of high T_c superconducting perovskites

The synthesis procedures (solid state and solution) used to produced YBa₂Cu₃O_7-x superconducting material in bulk or thick film form are briefly reviewed. Our results indicate that a solution technique (sol-gel process) permits lower reaction temperatures and yields dense (90%) and homogeneous ceramics with conducting properties which, in the normal states, tend toward those obtained on single crystals. However, independent of the synthesis technique used, the critical currents I_c remain low probably because of the presence of carbon or carbonate at the grain boundaries. Stable, viscous gels were used to prepare superconducting thick films on various substrates and problems specifically associated with thick film processing (i.e. film adhesion and reaction with the substrate) are discussed. Solid state reactions have been used to perform doping studies and to produced 3d-metal-substituted perovskites YBa₂Cu_3-xM_xO_y-y in which the oxygen content has been found to depend upon the nature and concentration of the dopant (i.e. M).