Yttrium. Barium- Copper Oxide Superconductors eThis ceramic YBa Cu,O-6 Ba material was the first of the high (YBa yCu perconductors to Oxygen Deficient ange at a Triple Perovskite temperature above the liquid nitrogen absent oxyge temperature (77 K Properties 8 value YBa. CugO, superconductor YBa CugO7-8 at temperature T. As 8 1)T decreases YBayCugOs semiconductor oxygen lost from base of from orthorhombic to unit cell tetragonal rearrange in base T= tetragonal Changing Properties? Oxides Superconductors Perovskite structure Can substitute many elements into YBa2Cu3O7 tructure BAlun Y→ lanthanides· no change in T ●Ym Y=other elements'decrease in Te Ba→Sr,Ca· decrease in t Cu= transition metals. decrease in T Cu→Au· very slight increase? Ba→La· very slight increase? Generally detrimental rIght: Removal of 2/9 of oxy gens gives defect perovskite structure, O-s(xd0.2)"123 Superconductor C N Ba= 10, C.N. Y=88 Yttrium-Barium-Copper Oxide This ceramic material was the first of the high temperature superconductors to make the phase change at a temperature above the liquid nitrogen temperature (77 K). Superconductors YBa2Cu3O7-d Perovskite? (YBa2 )Cu3O9-x Oxygen Deficient Triple Perovskite Crosses mark absent oxygen Properties YBa2Cu3O7 superconductor - resistance lost completely at temperature Tc YBa2Cu3O6 semiconductor - oxygen lost from base of unit cell YBa2Cu3O7-d As d increases: 1) Tc decreases 2) symmetry changes from orthorhombic to tetragonal (oxygen atoms rearrange in base) O = orthorhombic T = tetragonal d value Changing Properties? Can substitute many elements into YBa2Cu3O7 structure: Y Þ lanthanides - no change in Tc Y Þ other elements - decrease in Tc Ba Þ Sr, Ca - decrease in Tc Cu Þ transition metals - decrease in Tc Cu Þ Au - very slight increase? Ba Þ La - very slight increase? Generally detrimental! Oxides Superconductors vs Perovskite Structure Left: 3perovskite unit cells, CaTiO3 × 3 = Ca3Ti3O9 Center: Replace Ca with Ba, Y; Replace Ti with Cu® YBa2Cu3O9 orthorhombic unit cell count Right: Removal of 2/9 of oxygens gives defect perovskite structure, YBa2Cu3O7 -d (x»0.2) “123”Superconductor C.N. Ba = 10, C.N. Y = 8