Analysis of Ceramic Superconductors

The superconductor, YBa2Cu307 s (abbreviated as the 123 conductor), can be obtained by baking a mixture of Y2O3, and BaC03, and CuO in a proper ratio. The product is normally a mixture of an orthorhombic form (0 5 1) which is superconducting and a tetragonal form (5 = 1) that is an insulator. The Tc increases as 5 approaches 0. 

and Biu species, respectively, in the D2h point group. On the other hand, the 10 atoms, 2Ba, 2Cu(2), 20(2), 20(3), and 20(4) are at the C21 sites. As shown in Table 1.27, each pair of these atoms possess six degrees of vibrational freedom (2AiH-2 1 +2 2)5 which are split into Ag + B2g + B g - -Bin - under D2h symmetry. 

Similar calculations on the tetragonal unit cell (YBa2Cu306) show that 10 vibrations AAig- -Big- -3Eg) are Raman-active while 11 vibrations (5A2i H-6 J are IR-active under symmetry. 

TABLE 1.28. Vibrational Analysis for Orthorhombic Form of YBa2Cu307 5 Using the Correlation Method 

Axial motion of the 0(4) atoms 0(2)—Cu(2)—0(3) bending with the two O atoms moving in phase 

---