Correlation Between Enhanced ${\rm T}_{\rm c}$, AC Magnetic Irreversibility Line and Heat Treatment in High ${\rm T}_{\rm c}$ Superconductors

We report here on the preparation, resistivity, AC magnetic susceptibility measurements and effect of heat treatments in (Y
_1-x
Sm
_x
)(SrBa)Cu
₃
O
_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 δ
Tc
(
x
)=
Tc
[
AO
]-
Tc
[
O
] and δ
K
^'
(
x
); and between
Tc
(
x
) ,
d
[
Cu
(2)-
Y
/
Sm
](
x
) distance and the number
psh
(
x
) of holes by Cu(2)-O
₂
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.