CuO: X-ray single-crystal structure determination at 196 K and room temperature

Abstract

AbstracL An x-ray singleclystal determination of ihe CuO stmture has been made at 196 K, i.e. below the N6el temperature 230 K, and, as a check, the crystal smclure a1 m m temperature was also determined. The correct space p u p for lhe structure at bolh temperatures was found lo be C c . Earlier mulls of magnnk and neutmn diiimction measuremenls can be explained as antifemmagnetic coupling betwgn copper atoms via oxygen (superexchange) in chains running in the [I 0-11 direction. The s " a l results show changes with temperature in Cu-0 distances in these chains in each -Cu-(M1group lhe longer distance is increased and the shorter decreased when passing from 196 K to m m temperature. This implies a weaW antiferromagnetic mupiing at room temperature. The re6nement of CuO-stmctun at r w m temperature reponed earlier by Asbrink and Norrby (1970) showed the symmetry to be CZ/e. An attempt to refine CUO in the space group C e with the old data was not successful. The diffeerent m u l k obtained Hith different aystals are tentatively explained from published observations regarding valence fluctuations in CuO and non-stoichiometry caused by cation vacancies.

Cupric oxide nanoflowers synthesized with a simple solution route and their field emission

“…2. Except for the three peaks attributable to metallic Cu, all the other peaks are consistent with the characteristic diffraction peaks of monoclinic CuO [23], indicating that the nanoflowers were phase-pure CuO in chemical composition.…”

Cu-doped ceria: Oxygen vacancy formation made easy

“…2b; Table 1) we find that it is even easier to create an O vacancy: now E vac is only 0.30 eV. The coordination around Cu is here 4-fold, with Cu-O bond lengths similar to those in the CuO crystal structure [24], where Cu 2+ has four O neighbors within 1.90 to 2.00 Å and the next-nearest O neighbors reside 0.8 to 0.9 Å further away. Also here the four Ce cations surrounding the vacancy are (nominally) Ce 4+ and their Bader charges differ very little from pure CeO 2 (or unreduced Cu-doped CeO 2 ), mainly because the O vacancy reinstates the charge balance in the system and remedies the shortage of electrons caused by the lower valence of Cu (2+) compared to Ce (4+), i.e.…”

Birefringence and polarization rotation in resonant x-ray diffraction

“…15) 7 and, in common with all noncubic crystals, exhibits birefringence at absorption edge resonances. The material is multiferroic just below the paramagnetic transition at T N2 = 230 K and above T N1 = 213 K. 8 Below T N1 it is an antiferromagnet with an ordering wave vector q = (1/2,0, −1/2).…”