**3.1. Crystalline structure**

The X-ray diffraction spectra of all the samples are shown in **Figure 1** [8]. After the [AO] heat treatment, the reflections were sharper so the samples were well crystallized. The [AO] heat treatment increases the orthorhombic cleaving. For example, the (123) and (213) peaks at 2θ ≈ 58.5° (and (200) and (006) reflections at 2θ ≈ 47°) which were ill-resolved for the [O] samples were clearly identified after the [AO] heat treatment, as shown in **Figure 1**. Some weak unidentified impurity peaks (marked by crosses in **Figure 1(a)** were seen in the [O] samples and their amplitudes increase with x. They disappeared after the [AO] treatment shown in **Figure 1(b)**. This indicates an improvement of crystallographic quality of the samples [AO].

In **Figure 2** we show, respectively, the variation of the parameters a, b, c and the volume V of the unit cell obtained with Rietveld refinement [9] as a function of x and heat treatment. When x increases, the lattice parameter a (c and the volume V of the unit cell) increased but b is constant leading to a decrease of the orthorhombicity (ε = (b − a)/(b + a)) ε [O] in **Figure 3**. The substitution of Y+3 (0.893 Å) by the rare earth Sm+3 (0.965 Å), with a superior ionic radius, leads to a linear increase of c and V.

**Figure 1.** XRD (Cu Kα) patterns of (Y1−xSmx )SrBaCu<sup>3</sup> O6+z as a function of x. (a) Samples [O] annealed in oxygen at 450°C, (b) samples [AO] heated in argon at 850°C followed by annealing in oxygen at 450°C (x = impurity peaks).

**Figure 2.** Variation of the parameters a, b and c of (Y1−xSmx )SrBaCu<sup>3</sup> O6+z as a function of x and heat treatment in the left. The unit cell of (Y1−xSmx )SrBaCu<sup>3</sup> O6+z in the right.

**Figure 3.** Variation of the orthorhombicity of (Y1−xSmx )SrBaCu<sup>3</sup> O6+z as a function of x and heat treatment.

The orthorhombicity depends strongly on the Sm content x. When x increases from 0 to 1, ε decreases quickly from 8.24 × 10−3 to 1.5 × 10−3 in the samples [O] in **Figure 3**. This indicated a structural phase transition from orthorhombic to tetragonal. ε decreases slowly from 9.9 × 10−3 to 5.24 × 10−3 with an orthorhombic symmetry in the samples [AO]. We found also that the orthorhombicity depends strongly on the heat treatment [AO]. For each x, the latter increased the orthorhombicity (for 0 ≤ x ≤1). The increase was maximum, from 1.5 × 10−3 to 5.24 × 10−3 for x = 1 in [12].

from 81.7 K (for x = 0) to 81.2 K (for x = 0.2) (like in the samples [O]) and then increases to 85 K

in **Figure 5**. The [AO] heat treatment makes the coupling of the superconducting grains by Josephson junctions took place at higher temperature. This effect is revealed by the net dis-

of 6 K was observed in SmSrBaCu<sup>3</sup>

O6+z as a function of x(Sm) following the [O] and [AO] heat treatments.

O6+z as a function of temperature. (a) Heat treatment [O], (b) heat treatment [AO].

Effects of Isovalent Substitutions and Heat Treatments on Tc, Orthorhombicity, Resistivity, AC…

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for x ≥ 0.4 and decreases

O6+z [AO] [8].

(for x ≥ 0.4)

O6+z. For each x, the [AO] heat treatment increases Tc

For each x, the [AO] heat treatment increases ε (for 0 ≤ x ≤ 1) in **Figure 3** and Tc

for SmSrBaCu<sup>3</sup>

**Figure 5.** Tc

**Figure 4.** χ′ and χ″ of (Y1−xSmx

)SrBaCu<sup>3</sup>

it for x < 0.4. A maximum of increase in Tc

and Tp of (Y1−xSmx

placement of Tp to higher temperature for x ≥ 0.4.

)SrBaCu<sup>3</sup>
