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In order to access the overdoped regime of the YBa 2 Cu 3 O y phase diagram, 2 % Ca is substituted for Y in YBa 2 Cu 3 O y ( y = 7.00,6.93,6.88,6.76). Raman scattering studies have been carried out on these four single crystals. Measurements of the superconductivity-induced renormalization in frequency (∆ω) and linewidth (∆2γ) of the 340 cm −1 B 1g phonon demonstrate that the magnitude of the renormalization is directly related to the hole concentration (p), and not simply the oxygen content. The changes in ∆ω with p imply that the superconducting gap (∆ max ) decreases monotonically with increasing hole concentration in the overdoped regime, and ∆ω falls to zero in the underdoped regime. The linewidth renormalization ∆2γ is negative in the underdoped regime, crossing over at optimal doping to a positive value in the overdoped state.

The temperature dependences of the linewidth and frequency of the 340-cm ' Raman-active phonon have been measured in five lightly twinned crystals of YBa2Cu30, with different oxygen concentrations x. The observed changes in the linewidth and frequency that occur for temperatures below the critical temperature have been found to depend strongly on the value of x within the region 6.85~x &7.0. The linewidth and frequency dependences for T & T, . result in superconducting gap energy estimates which indicate that 2h, decreases for oxygen concentrations x &6.95 and remains approximately constant for 6.85&x 6.95. Given the low level of impurities in these crystals these results are attributed to variations in the hole concentrations which arise primarily from variations in the oxygen content.