COMPARISON OF THE RAMAN-ACTIVE PHONONS OF YBA2CU3O7 CRYSTALS GROWN IN GOLD AND ZIRCONIA CRUCIBLES

Three single-domain crystals of YBa2Cu3O7 grown in either gold or zirconia crucibles have been studied by Raman scattering. Two of the crystals were annealed and mechanically detwinned after growth, while the third was only detwinned. There are crystal-to-crystal variations in the absolute values of the phonon line widths. However, the line widths of the A(g) phonons exhibit nearly the same temperature trends in the three crystals. Below T(c), the phonons at 340, 440 and 500 cm-1 sharpen dramatically, sharpen slightly, and broaden, respectively. When interpreted within the framework of conventional theories of superconductivity, the line-width behavior supports a superconducting energy gap 2DELTA between 440 and 500 cm-1 (2DELTA = 6.8-7.7 k(B)T(c)). The line shapes of the 120, 150, 340 and 500 cm-1 phonons can be asymmetric. Only the 500 cm-1 phonon becomes less symmetric below T(c). The intensities of the A(g) phonons vary little with temperature below T(c). Raman peaks, possibly defect modes, are observed at approximately 232 cm-1 and approximately 143 cm-1 in the as-grown crystal, but not in annealed crystals. The frequency of the approximately 143 cm-1 peak largely decreases with decreasing temperature, opposite of the behavior found for the adjacent A(g) phonons. In addition, the temperature dependence of the B2g and B3g phonons of gold-grown YBa2Cu3O7 has been studied. For the most part, the frequency behavior is not remarkable. In gold-grown YBa2Cu3O7, the line widths of 11 phonons from about 70 to 500 cm-1 have been measured above and below T(c). Only the phonon at 500 cm-1 is found to broaden below T(c).