Publications by authors named "Viktor Poltavets"

Shrimp shell waste obtained from Louisiana Gulf shrimp (Litopenaeus setiferus) was heat-treated at varying temperatures and ground into a powder by ball-milling. The powder was used with and without surface treatment with maleic anhydride or stearic acid to form shrimp shell - polylactic acid (PLA) composite granules by solution processing and mechanical grinding. These granules were used as feedstock for the extrusion of composite filaments.

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Transition metal (M) oxides with MO2 triangular layers demonstrate a variety of physical properties depending on the metal oxidation states. In the known compounds, metal oxidation states are limited to either 3+ or mixed-valent 3+/4+. A multistep soft chemistry synthetic route for novel phases with M(2+/3+)O2 triangular layers is reported.

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A chimie douce solvothermal reduction method is proposed for topotactic oxygen deintercalation of complex metal oxides. Four different reduction techniques were employed to qualitatively identify the relative reduction activity of each including reduction with H(2) and NaH, solution-based reduction using metal hydrides at ambient pressure, and reduction under solvothermal conditions. The reduction of the Ruddlesden-Popper nickelate La(4)Ni(3)O(10) was used as a test case to prove the validity of the method.

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The Ni1+/Ni2+ states of nickelates have the identical (3d(9)/3d(8)) electronic configuration as Cu2+/Cu3+ in the high temperature superconducting cuprates, and are expected to show interesting properties. An intriguing question is whether mimicking the electronic and structural features of cuprates would also result in superconductivity in nickelates. Here we report experimental evidence for a bulklike magnetic transition in La4Ni3O8 at 105 K.

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Electronic structure calculations were performed for the mixed-valent Ni(1+)/Ni(2+) nickelate La3Ni2O6, which exhibits electronic instabilities of the Fermi surface similar to that of the isostructural superconducting La2CaCu2O6 cuprate. La3Ni2O6 shows activated hopping, which fits to Mott's variable-range-hopping model with localized states near the Fermi level. However, a simple local spin density approximation calculation leads to a metallic ground state.

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Single-phase Ln4Ni3O8 (Ln = La, Nd) nickelates were synthesized and their crystal structures were determined by Rietveld refinement of powder neutron diffraction data. The crystal structures of these mixed-valent Ni1+/Ni2+ phases belong to the T'-type and are built by intergrowth of LnO2 fluorite layers with triple NiO2 infinite-layer structural blocks. The major driving force of transformation of the LnO rock-salt block of the parent Ln4Ni3O10-delta Ruddlesden-Popper phases to the fluorite arrangement in the reduced Ln4Ni3O8 phases is attributed to internal structural stress.

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New mixed-valent, Ni1+/Ni2+, metastable nickelate, La3Ni2O6, was synthesized by low-temperature reduction of La3Ni2O7 with CaH2. The crystal structure of La3Ni2O6 (space group: I4/mmm, a = 3.9686(1) A and c = 19.

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