SCHEDULED MAINTENANCE
Abstract
Na- or K-substituted PrMnO3 and NdMnO3 phases have been prepared using neutral NaCl or KCl fluxes at a relatively low temperature of 900 °C. These flux syntheses not only promote the reaction at low temperatures but also act as a source of the alkali metal in the final product. The structures of these oxides have been refined by the powder X-ray Rietveld method and confirmed by the electron diffraction studies. All these phases crystallize in the orthorhombic structure (space group Pbnm) and are ferromagnetic insulators. Na-doped mixed rare-earth manganites of the formula (Pr1 − xLax)1 − yNayMnO3 (0 ≤ x ≤ 0.80; 0.08 ≤ y ≤ 0.15) have also been synthesized in NaCl flux; among these mixed rare-earth manganites those crystallizing in rhombohedral structures are ferromagnetic metals (FMM), and those in orthorhombic structures are ferromagnetic insulators (FMI). The phase diagram of average A-site radii vs. ferromagnetic transition temperature, Tc, of the stoichiometric phases has been constructed here and compositions with 〈rA〉 ≤ 1.20 Å crystallizing in the orthorhombic structures fall in the ferromagnetic insulating region. Compositions with 〈rA〉 ≥ 1.20 Å crystallize in the rhombohedral structures and these are ferromagnetic metals.
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