Correlation Between Enhanced ${\rm T}_{\rm c}$, the Unit Cell Volume and AC Magnetic Shielding in Argon Preheated $({\rm Y}_{1-{\rm x}}{\rm Eu}_{\rm x})({\rm SrBa}){\rm Cu}_{3}{\rm O}_{6+{\rm z}}$

We report here on the preparation, X-ray diffraction with Rietveld refinement, resistivity and AC magnetic susceptibility measurements of (Y
_1-x
Eu
_x
)(SrBa)Cu
₃
O
_6.94
. Each sample was subject to two types of heat treatment: oxygen annealing [O] and argon annealing followed by oxygen annealing [AO]. For each x, the [AO] treatment increases the orthorhombicity ε (for 0 ≤ x ≤ 1), T
_c
(for x ≥ 0.45) and by 6 K to 87 K for x = 1 [AO], and the distance d[Cu(1)-Sr/Ba] (decrease T
_c
) for x <; 0.4 and decrease it (increase T
_c
) 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. There was a remarkable improvement in the shielding effect S (amplitude of χ
^'
(
T
)) in the case of the samples [AO] at all T <; T
_c
and for any applied field for x >; 0.5. For each x and heat treatment, S(x) decreases when H
_dc
and the temperature increase. Remarkable correlations were observed. A combination of several factors such as decrease in d[Cu(1)-(Sr/Ba)] ; increase in cationic and chain oxygen ordering; p
_Sh
and in-phase purity for the [AO] samples may account for the observed data.