Synthesis, single-crystal structure and magnetic properties of orthorhombic CuNb2O6

Abstract

The conditions necessary for the synthesis of the two reported polymorphs of CuNb,O, from the binary oxides have been investigated. The black, orthorhombic phase has been prepared in a pure crystalline form and its single-crystal structure determined. It is isomorphous with the M"Nb,O, columbite system (orthorhombic, a = 14.019(11) A, b = 5.623(7) A, c = 5.107(7) A, space group Pbcn) but the CuO, octahedra display a large tetragonal distortion [Cu-0, 1.976(6) x 2, 1.973(6) x 2, and 2.383(6) x 2 A]. Above 225 K the compound is magnetically dilute and obeys the Curie law (peff= l.91pB), whereas Curie-Weiss behaviour was observed between 225 and 50 K (8= -30 K) with a maximum susceptibility at 20 K. The magnetic data have been analysed in terms of a onedimensional antiferromagnetic chain model.The yellowish-green, monoclinic phase is more difficult to prepare in a pure form than the black, orthorhombic phase. Some provisional details for its preparation are reported.

The Synthesis, Properties, and Applications of Columbite Niobates (M2+Nb2O6): A Critical Review

“…Pullar et al 22 reported a mixed phase CuNb 2 O 6 up to 1200°C, when it melted, and above 950°C a liquid phase lead to exaggerated or discontinuous grain growth (DGG). It has been suggested that once the monoclinic phase has been formed it is hard to obtain the single orthorhombic phase, although it can be obtained by annealing at 900°C, 34 stress induced by grinding the monoclinic phase, 35 or by heating to 1100°C (producing unsintered powder with a grain size of 15 μm) 36 …”

Li‐Driven Copper Extrusion/Re‐injection in Various Cu‐based Oxides and Sulfides

“…These layers are stacked along [001], and the copper ions set in a linear surrounding ensure the cohesion of the structure. The structure of CuNb 3 O 8 23 and CuNb 2 O 6 24 can be described in one step as they are both related to the same α-PbO 2 structure type ( Fig. 12).…”

A new approach for the determination of multiple cation locations and ordering, using the example of natural and heat-treated columbites

“…These minerals are economically important since they are the major source of tantalum. In addition, they are very interesting from a fundamental point of view since they present interesting physical properties which have motivated numerous investigations in the past two decades (Eicher et al, 1986;Wenger et al, 1991;dos Santos & Oliveira, 1992;Kremer & Greedan, 1998;Mello et al, 1999;Antonietti et al, 2001;Eibschü t et al, 1967;Drew et al, 1993;Heid et al, 1996;Beurlen et al, 2008). Much fundamental research on the physical properties has also been performed on synthetic AB 2 O 6 compounds (Felten, 1967;Esmaeilzadeh & Grins, 2002).…”