Electronic properties of transition-metal oxides-II: Cation distribution amongst octahedral and tetrahedral sites

Electronic properties of transition-metal oxides—I: Distortions from cubic symmetry

https://hal.archives-ouvertes.fr/hal-02503180/document

The transformation of Cu(OH)2 into CuO, revisited

Single-crystal neutron diffraction measurements have been used to study the long-range magnetic ordering in cupric oxide, CuO. An incommensurate antiferromagnetic structure forms below the Neel temperature on 230(1) K, with a propagation vector (0.506(1)a*-0.483(1)c*) which remains constant down to a magnetic phase transition at 213(1) K. Below the latter temperature, the structure remains antiferromagnetic with a commensurate propagation vector (1/2 0-1/2), and this structure persists to the lowest temperature reached in the investigation (20 K). The arrangement of the copper moments in both phases is such that the n-glide perpendicular to the b axis of the monoclinic cell, space group C2/c, does not reverse the direction of the spin. The two magnetic sublattices related to the C-face-centring scatter in phase quadrature and the relative directions of the spin on them could not be determined. Good agreement is obtained for the commensurate phase with a multipole model for the copper magnetisation density and spins of 0.65(3) mu B directed parallel to b. The lower sublattice magnetisation in the incommensurate phase precluded a meaningful multipole fit, but a reasonable agreement is obtained with a model in which the spins rotate in the a-c plane following an elliptical envelope with major axis directed 33(2) degrees to c in beta obtuse and a maximum moment of 0.38(2) mu B at 215 K. The paramagnetic scattering at ambient temperature and 550 K was measured to try to find the origin of the peak in the susceptibility. No significant paramagnetic scattering could be obtained from a powdered sample although the sensitivity of detection was some five times that required to observe the scattering from a Cu2+ ion in an ideal paramagnet.

https://iopscience.iop.org/article/10.1088/0022-3719/21/15/023/pdf

Magnetism in cupric oxide

The magnetic susceptibility of cupric oxide

The goniometrical measurements of N. Story-l\\laskelyne ) on crystals of tenorite (also called melaconite) found with cuprite and chrysocolla in a chloritic veinstone from Lostwithiel, Cornwall, satisfy the symmetry requirements of the monoclinic system, and the crystal habit illustrated in the drawing of Story-l\\1askelyne is clearly that of the holohedral class of the monoclinic system. ~Ioreover, as A. Scacchi) has pointed out, the goniometrical measurements of J. J enzsch ) on artificial crystals of cupric oxide formed near a flue in a smelterhearth during roasting of copper matte with sodium chloride at Freiberg, yield calculated elements agreeing with those of Story-1\\Iaskelyne, and the crystals drawn by J enzsch exhibited the same habit and twinlaw as those of Story-·Maskelyne. J enzsch interpretE<d his crystals as orthorhombic but his measurements do not satisfy orthorhombic symmetry requirements either qualitatively or quantitatively. Numerous inconsistencies and errors in detail occur in the papers of Story-~Iaskelyne, of Jenzsch, and of Scacchi. For this reason we have carried out geometrical and optical, as well as X-ray measurements, sufficient to establish our conclusions without the use of previous experimental results. At the same time our conclusions are in agreement with previously reported experimental facts. Our conclusions rest on optical, geometrical, and X-ray study of the thin natural tenorite crystals deposited on the lavas of Mount Vesuvius, on X-ray study of chemically pure artificial cupric oxide powder, and finally on geometrical and X-ray study of single faceted crystals of tenorite prepared for the purpose hy recrystallization in molten sodium hydroxide.

C. J. Ksanda

Papers

Geometrical and Optical Properties, and Crystal Structure of Tenorite