Correlation Between Enhanced , AC Magnetic Irreversibility Line and Heat Treatment in High Superconductors

We report here on the preparation, resistivity, AC magnetic susceptibility measurements and effect of heat treatments in (Y_1-xSm_x)(SrBa)Cu₃O_6+z. Each sample was subject to two type of heat treatment: oxygen annealing [O] and argon annealing followed by oxygen annealing [AO]. An enhancement of T_c[AO] was observed for x ≥ 0.4. In the normal state, the [AO] treatment reduced the linear resistivity parameters indicating a diminution of the interaction of carrier charges with phonons. Tc(χ^') and Tc(ρ = 0) were in good agreement. An enhancement of the AC irreversibility line H(t = Tp/Tc) was observed due to [AO] treatment for x >; 0.5 indicating an improvement in the pinning properties. The data were analysed with the relation H = K^'(1-t)n . Remarkable correlations were observed between δTc(x)=Tc[AO]-Tc[O] and δK^'(x); and between Tc(x) , d[Cu(2)-Y/Sm](x) distance and the number psh(x) of holes by Cu(2)-O₂ superconducting planes. A combination of several factors such as decrease in d[Cu(1)-(Sr/Ba)] for x >; 0.4; increase in cationic and chain oxygen ordering; p_sh and in-phase purity for the [AO] samples may account for the observed data.