RAMAN-SCATTERING ON YBA2CU3O7-DELTA SINGLE-CRYSTALS WITH VARIABLE OXYGEN-CONTENT

Light scattering investigations have been performed on YBa2Cu3O7-delta single crystal with 0 < delta < 1. Softening and the stiffening in frequency of the 5 Ag normal modes originating from the YBa2Cu3O7 structure have been observed as the oxygen content decreases. Moreover, for intermediate oxygen content: 0.4 less-than-or-equal-to delta less-than-or-equal-to 0.5, the existence of a new structural phase, the Ortho II phase, has been detected. This new phase is defined by the double elemental unit cell Y2Ba4Cu6O13 and establishes the connection between the orthorhombic YBa2Cu3O7 metallic phase related to the D1(2h) space group and the tetragonal YBa2Cu3O6 insulator phase related to the D1(4h) space group.