CRYSTAL-CHEMISTRY AND PHASE-EQUILIBRIA STUDIES OF THE BAO(BACO3)-R2O3-CUO SYSTEMS .4. CRYSTAL-CHEMISTRY AND SUBSOLIDUS PHASE RELATIONSHIP STUDIES OF THE CUO-RICH REGION OF THE TERNARY DIAGRAMS, R = LANTHANIDES

In theBaO(BaCO3){single bond}R2O3{single bond}CuOsystems, whereR =lanthanidesand yttrium, general trends of phase formation, solid solution formation, and phase relationships are correlated with the ionic size ofR.In air at 950°C the phase relationships in the CuO-rich region of these ternary diagrams progressively change from the La system through the Nd, Sm, Eu, Gd, Y, Ho systems to the Er system. First, the La system has the greatest number of ternary compounds. Second, the superconductor material,Ba2RCu3O6+x,exhibits a solid solution ofBa2-zR1+zCu3O6+xfor the first half of the lanthanide elements with a range of formation which varies with the ionic size ofR.Third, a trend is observed regarding the tie-line connections betweenBaR2CuO5, CuO, the phasesBa2-zR1+zCu3O6+x, and the binary phaseR2CuO4orR2Cu2O5.For the first half of the lanthanides, except for La, a compatibility join is found to connectR2CuO4and the tetragonal end member of theBa2-zR1+zCu3O6+xphase. In systems whereRhas a smaller ionic size,R =Euand beyond, the tie-line connection switches to join theBaR2CuO5phase and the CuO phase. ForR =Dyand beyond, the binary phaseR2CuO4is replaced by the binary phaseR2Cu2O5. © 1990 Academic Press, Inc. All rights reserved.