The effects of chemical doping and hydrostatic pressure on T-c of Y1-yCayBa2Cu3Ox and NdBa2Cu3Ox single crystals

We studied T-c of YBa2Cu3Ox (Y123), Y0.89Ca0.11Ba2Cu3Ox (YCa123) and NdBa2C u3Ox (Nd123) single crystals with various oxygen contents x. Compared to T- c(x) of Y123 the T-c(s) curves of YCa123 are shifted to lower oxygen conten ts and the maximum transition temperature T-c,T-max decreases with increasi ng Ca content whereas in Nd123 T-c(x) is shifted to higher oxygen contents and T-c,T-max is increased. According to the universal parabolic T-c(n(h)) behavior the differences an T-c(x) of Y123, YCa123 and Nd123 can be ascribe d to different hale concentrations nr, in the CuO2 planes caused by doping via changes in chemistry or structure. In order to study the influence of s tructural changes on T-c we examined the hydrostatic pressure effect dT(c)/ dp (p less than or equal to 0.6GPa). rn the underdoped region, at n(h) appr oximate to 0.11, the examined compounds shaw a peak in dT(c)/dp which is ve ry pronounced for systems with well ordered CuO chains. As this peak occurs at the same nh in all investigated systems it is not caused by oxygen orde ring, but its origins might be found in a strong influence of lattice defor mations on the electronic structure.