Abstract
The new low temperature phase LT-Tm 2BaNiO 5 has been prepared as a brown-tobacco colored sample. X-ray diffraction data reveal that this phase shows orthorhombic symmetry, space group Pnma. The lattice parameters are a = 12.1939(2) Å, b = 5.665(1) Å and c = 6.9704(1) Å. When this LT-form is heated for 12 hours at 1600 K the HT-form is obtained as a dark-green colored sample, showing orthorhombic symmetry, space group Immm. Magnetic susceptibility data for this HT-form reveal that the nickel ions are 1D-antiferromagnetically correlated along the chains of flattened (NiO 6) octahedra above room temperature. The maximum observed in the susceptibility at 8.3 K has been attributed to the 3D-antiferromagnetic ordering in both the nickel and thulium sublattice. This result has been confirmed from the neutron diffraction studies and the Néel temperature is 14 K. However, because of its different structure neither a 1D nor a 3D antiferromagnetic order has been found in the case of the new LT-Tm 2BaNiO 5 oxide.
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