Structural and magnetic properties of Ba{sub 3}La{sub 3}Mn{sub 2}W{sub 3}O{sub 18}

A quaternary phase, Ba{sub 3}La{sub 3}Mn{sub 2}W{sub 3}O{sub 18}, was synthesized in reduced atmosphere (5% H{sub 2}/Ar) at 1200 deg. C and characterized by using powder X-ray diffraction, electron diffraction and high resolution TEM. Ba{sub 3}La{sub 3}Mn{sub 2}W{sub 3}O{sub 18} crystallizes in rhombohedral space group R3-bar m with the cell parameters, a=5.7371(1)A and c=41.8336(5)A, and can be attributed to the n=6 member in the B-site deficient perovskite family, A{sub n}B{sub n-1}O{sub 3n}. The structure can be described as close-packed [La/BaO{sub 3}] arrays in the sequence of (hcccch){sub 3}, wherein the B-site cations, W and Mn, occupy five octahedral layers in every six octahedral layers, which leave a vacant octahedral layers separating the 5-layer perovskite blocks. The B-cation layers in the perovskite block alternate along the c-axis in a sequence of W{sup 6+}-Mn{sup 2+}-W{sup 5+}-Mn{sup 2+}-W{sup 6+}. The bond valence calculation and optical reflection spectrum confirm the presence of W{sup 5+}. This compound behaves paramagnetically in wide temperature range and weak antiferromagnetic interaction only occurs at low temperatures.