POLYMERIZABLE COMPLEX SYNTHESIS OF MULTI- COMPONENT OXIDES INCLUDING HIGH-TEMPERATURE SUPERCONDUCTING OXIDES

摘要

The "polymerizable complex (PC)" technique (first documented as a patent by Pechini in 1967) offers a convenient means for fabricating complex multi-component oxides. The method is based on the formation of a polymer resin precursor in which various metal ions can be uniformly distributed keeping their initial stoichiometric ratio. The approach allows for the development of multicomponent systems with very complex compositions. Feasibility of the PC method with respect to homogeneous distribution of dopants within the lattice was demonstrated on the ceramic synthesis of plycrystalline compounds, Y_(1-x)Ca_xBa_2Cu_(2.8)Co_(0.2)O_(6+d) (x=0-0.3). T_c determined precisely from the complex magnetic susceptibility measurements was systematically increased from 57 K for the x=0 sample up to 89 K for the x=0.3 sample. The restoration of T_c with Ca was interpreted as a consequence of reintroduction of holes on the Cu(2)O_2 planes; which was supported from the Raman scattering measurements, where specific modes involving atoms in the Cu(2)O_2 layers decrease in intensity with Ca indicating an increased metallic screening in the Ca-rich samples.