**3. Results**

The four distinct crystallographic sites Y, Ba, Cu plane, and Cu chain can be substituted

O6+z (Ln = rare earth) can be synthesized with

(with 0 ≤ x ≤ 0.5). They concluded that in order to have

O6+z. We found that the effect of heat treatments on these properties

99.999% pure, BaCO<sup>3</sup>

depend sensitively on the

O3 , Sm<sup>2</sup> O3

with a purity of 99.99%).

, CuO)

Cu<sup>3</sup>

Tc = 92 K. All these compounds show an orthorhombically distorted oxygen-deficient triple-

oxygen content (6 + z) [3]. Wada et al. [4], Izumi et al. [5] studied the structural and supercon-

maximal, this structure must have an ordered arrangement of La and Ba along c axis with

We want to see if an isovalent substitution of Ba+2 by Sr+2 with smaller ionic radius can modify the results discussed above when Y+3 is replaced by the rare earth Sm+3 with bigger ionic radius. Understanding the effect of the Y and Ba atomic plans on the superconductivity in these compounds, we have studied the structural, superconducting and magnetic proper-

All these chemicals were thoroughly mixed in desired proportions and calcined at 950°C in air for 12–18 h. The obtained ceramic was ground, mixed, pelletized and heated in air at 980°C for 16–24 h. This was repeated twice. For each sample, the circular pellets were subjected to heat treatment in oxygen at 450°C for 60–72 h and furnace cooled. This was denoted as sample [O]. X-ray diffraction spectra of the samples were measured with Philips diffractometer fitted with a secondary beam graphite monochromator and using Cu Kα (40 kV/20 mA) radiation. The angle 2θ was varied from 20° to 120° in steps of 0.025°and the counting time per step was 10 s.

A detailed description of the basic arrangement of the experiment of the AC magnetic susceptibility can be found in [6]. The sample in the form of a slab is placed in the magnetic field Hext = Hdc + Hac cos(ωt) with the static component Hdc and the AC component with the amplitude Hac and the frequency f = ω/2π. The sample's magnetic response was detected by a pick-up coil surrounding the sample. Superconducting transitions were determined by the measure of the real (χ′) and the imaginary (χ″) parts of the AC magnetic susceptibility as a function of temperature in Hac = 0.11 Oe and at f = 1500 Hz. Also, χ′ and χ″ were measured in

We used the Van Der Pauw method [7] for measuring resistivity ρ(T). The sample was attached to a cane in a cryostat with closed helium circuit with a cryogenic pump, a regulator of temperature (1 μA–10 mA) and 1 μV resolution digital voltmeter controlled with a computer. Tc

For each x, the same sample [O] was then heated in argon at 850°C for about 12 h, cooled to 20°C and oxygen was allowed to flow instead of argon and the sample was annealed at 450°C

an occupation factor of 0 and 1 for the oxygen at (1/2, 0, 0) and (0, 1/2, 0), respectively.

with different elements. Single-phase LnBa<sup>2</sup>

ducting properties of La1+xBa2−xCu<sup>3</sup>

130 Superfluids and Superconductors

)SrBaCu<sup>3</sup>

depended on the content of Sm.

**2. Experimental techniques**

0 < Hdc < 150 Oe with applied Hac.

with a purity of 99.999% and carbonates (SrCO<sup>3</sup>

The XRD spectra were resolved with Rietveld refinement.

was determined by both the measured χ′(T) and ρ(T).

Tc

ties of (Y1−xSmx

perovskite structure and both the orthorhombic distortion and Tc

Oy

We prepared the polycrystalline samples by solid-state sintering of oxides (Y<sup>2</sup>
