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Ε. Posnjak

Bio: Ε. Posnjak is an academic researcher. The author has contributed to research in topics: Crystal structure. The author has an hindex of 1, co-authored 1 publications receiving 66 citations.

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TL;DR: In this paper, the symmetry requirements of the monoclinic system were shown to be satisfied by Story-Iaskelyne's drawings of melaconite with cuprite and chrysocolla.
Abstract: 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

72 citations


Cited by
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TL;DR: In this paper, the distribution of transition-metal ions amongst octahedral and tetrahedral sites in oxides, particularly of the spinel type, is discussed from the viewpoint of crystal field theory.

390 citations

Journal ArticleDOI
TL;DR: In this paper, the distortions from cubic symmetry which occur in certain transition-metal oxides, particularly those with the spinel structure, are discussed in terms of crystal (ligand) field theory and it is shown that many such distortions, including all the large ones, are related in a simple fashion to the electronic configuration of the metal ion.

381 citations

Journal ArticleDOI
TL;DR: In this paper, the authors described the reaction process and corresponding vectorial relations between crystal parameters of copper hydroxide and oxide in aqueous basic solutions, showing that the transformation is a topotactic or pseudomorphic transformation owing to clear relationships between axes of the two solids.

281 citations

Journal ArticleDOI
TL;DR: In this article, a single-crystal neutron diffraction measurements have been used to study the long-range magnetic ordering in cupric oxide, CuO, and 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.
Abstract: 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.

244 citations

Journal ArticleDOI
TL;DR: In this paper, the magnetic susceptibility of high purity cupric oxide has been measured from 14°K to 1100°K, and the results were interpreted in terms of antiferromagnetic super-exchange, characterized by a Neel temperature of 230°K and a direct spin coupling with an energy of 730 cm −1.

144 citations