Preparation and general physical properties of polycrystalline PrBa₂Cu₃O_7-y obtained from sol-gel precursors

Polycrystalline samples of PrBa₂Cu₃O_7-y were prepared through two different routes: (a) Mixing Pr₆O₁₁, BaCO₃, and CuO; (b) sol-gel precursors. The samples were heat-treated in the temperature range 700 ≤ T ≤ 930 °C and under different atmospheres, (Argon and air). Oxidation of these compounds, based on the results of thermogravimetric analysis, TGA, was performed at low temperatures, from 300 to 400 °C, for time intervals as long as 120 h. The crystal structure was determined by measurements of X-ray powder diffraction and revealed that samples heat-treated at 810 °C in Ar and for 130 h have a tetragonal structure with lattice parameters c ∼ 11.88 Å. Oxygenated PrBa₂Cu₃O_7-y samples were found to have an orthorhombic structure with lattice parameter c ranging from 11.72 to 11.75 Å. Electrical resistivity ρ(T) measurements performed on these compounds revealed a semiconductor-like behavior in the temperature range 77 ≤ T ≤ 300 K. The magnetic susceptibility ρ(T) data showed a paramagnetic-like behavior from 5 to 300 K and a clear contribution of the crystalline electrical field (CEF) below 150 K. We have also found an antiferromagnetic ordering associated with the Pr sub-lattice at T_N ∼ 17 K. Evidence of superconductivity was not observed on our samples, in agreement with most of the results reported in the literature.