SYNTHESIS, STRUCTURE, AND PROPERTIES OF SODIUM OR POTASSIUM-DOPED LANTHANUM ORTHOMANGANITES FROM NACL OR KCL FLUX

Lanthanum and oxygen-deficient La(1-x-y)A(x)MnO(3-delta) (A = Na or K) ferromagnetic oxide phases have been synthesized from NaCl or KCl flu x, starting from La2O3 and MnCO3 at 900 degrees C. Composition of the final product could be varied by varying initial composition LayMnO3 ( 0.7 < y < 1). Final composition of these oxides was obtained from chem ical analysis of elements present. As the lanthanum content increased, Na or K content decreased and the structure changed from rhombohedral to orthorhombic symmetry. Mn4+ concentration was 27% in the sodium do ped manganite, La0.82Na0.13MnO2.93 with Curie temperature 325 K, and M n4+ was 25% in the potassium doped La0.82K0.08MnO2.89 with T-c of 310 K. Structure of these two phases have been refined from neutron diffra ction studies. Stoichiometric La(1-x)A(x)MNO(3) (A = Na or K) have bee n obtained for the initial, composition LayMnO3 (y = 0.85). Orthorhomb ic phases obtained were found to be Mn-deficient La1-xNaxMn1-x Mn1-yO3 (x similar or equal to 0.02; y similar or equal to 0.05), which were ferromagnetic insulators, even though total Mn4+ contents were as high as 29%. (C) 1998 Academic Press.