PHASE-SEPARATION, PSEUDOGAP AND IMPURITY SCATTERING IN THE HTS CUPRATES

NMR and phase studies on a wide range of cuprates as a function of hol e doping reveal many new systematic features. The 60K plateau in 123-l ike materials is consistent with generic electronic phase separation r ather than oxygen vacancy ordering. The normal-state pseudogap has a d -wave-like character and the same energy scale as superconductivity. C ontrary to ARPES data, the pseudogap energy is T-independent and does not vanish at T=T. The suppression of T-c by Zn substitution is consi stent with unitarity scattering with a d-wave order parameter in the p resence of a pseudogap.