Effects of substituting calcium for yttrium on the properties of YBa2Cu3O7- delta

Negative quantum interference between the electronic Raman scattering processes of CuO chains and CuO2 planes of heavily overdoped (Y, Ca)Ba2Cu3O(7-delta)

We found a strong X-Y anisotropy of the pair-breaking peak in the Raman scattering of heavily overdoped (Y, Ca)Ba2Cu3O(7-delta) (T(c) = 65 K). The pair-breaking peak is radically suppressed in the YY-polarized spectrum. We ascribe this anomaly to the effect of quantum interference between the Raman processes of the CuO-chain and the CuO2-plane electronic excitations that might take place as a result of the increase in the transfer matrix due to overdoping.

Cation disorder in Ga1212

Substitution of calcium for strontium in LnSr2-xCaxCu2GaO7 (Ln = La, Pr, Nd, Gd, Ho, Er, Tm, and Yb) materials at ambient pressure and 975 degrees C results in complete substitution of calcium for strontium in the lanthanum and praseodymium systems and partial substitution in the other lanthanide systems. The calcium saturation level depends on the size of the Ln cation, and in all cases, a decrease in the lattice parameters with calcium concentration was observed until a common, lower bound, average A-cation size is reached. Site occupancies from X-ray and neutron diffraction experiments for LnSr2-xCaxCu2GaO7 (x = 0 and x = 2) confirm that the A-cations distribute between the two blocking-layer sites and the active-layer site based on size. A quantitative link between cation distribution and relative site-specific cation enthalpy for calcium, strontium, and lanthanum within the gallate structure is derived. The cation distribution in other similar materials can potentially be modeled.