Hydrothermal synthesis of crednerite CuMn1-x M (x) O-2 (M = Mg, Al; x=0-0.08) structural characterisation and magnetic properties

A series of CuMn1-x M (x) O-2 (M = Mg, Al; x = 0-0.08) samples was prepared using the low-temperature hydrothermal method. Crednerite-type materials are obtained for a low level of substitution, i.e. up to x = 0.08, and transmission electron microscopy observations indicate that the average crystallite size decreases with an increase in x. The evolution of unit cell parameters in function of x, from Rietveld refinements using X-ray powder diffraction data, presents a distinct behaviour for both series, but corresponds in both cases to a regularisation of the triangular network in the (a, b) plane. The investigation of the structural, thermal and magnetic properties reveals that the substitution has a significant role on the magnetism in CuMn0.94M0.06O2 (M = Mg, Al). It was found that the Mg and Al substitution on the Mn site leads to a small increase in the magnetisation values at low temperature, although the particle size decreases, which can be related to a release of magnetic frustration

Hydrothermal synthesis of crednerite CuMn1-x M (x) O-2 (M = Mg, Al; x=0-0.08) structural characterisation and magnetic properties

International audienceA series of CuMn1-x M (x) O-2 (M = Mg, Al; x = 0-0.08) samples was prepared using the low-temperature hydrothermal method. Crednerite-type materials are obtained for a low level of substitution, i.e. up to x = 0.08, and transmission electron microscopy observations indicate that the average crystallite size decreases with an increase in x. The evolution of unit cell parameters in function of x, from Rietveld refinements using X-ray powder diffraction data, presents a distinct behaviour for both series, but corresponds in both cases to a regularisation of the triangular network in the (a, b) plane. The investigation of the structural, thermal and magnetic properties reveals that the substitution has a significant role on the magnetism in CuMn0.94M0.06O2 (M = Mg, Al). It was found that the Mg and Al substitution on the Mn site leads to a small increase in the magnetisation values at low temperature, although the particle size decreases, which can be related to a release of magnetic frustration

The Electrical Properties of Some Composite Materials Based on Sodium and Tantalum Oxides

Two samples of Na-Ta oxides were synthesized by the hydrothermal method at reaction temperatures of 160°C (sample A) and 200°C (sample B). For reference, a third sample of pure NaTaO₃ was prepared by the sol-gel method (sample C). Using X-ray diffraction, scanning electron microscopy, UV-vis diffuse reflectance spectra and electric measurements, structural, morphologic, spectroscopic and electric properties of samples were investigated. The structural characterization by X-ray diffraction revealed that samples A and B are mixtures of Na-Ta oxides (including NaTaO₃ and other compounds), whilst sample C is pure NaTaO₃. UV-vis diffuse reflectance spectra allowed evaluation of the band gap energy $(E_{g})$, resulting in 3.88 eV for sample A, 3.93 eV for sample B and 4.1 eV for sample C. Electrical resistivity measurements, over the temperature range 300-450 K, showed a typical semiconductor behavior of the investigated samples, with the effective activation energy, $E_{a}$ of 0.47 eV (sample A), 0.45 eV (sample B) and 0.82 eV (sample C). Based on the Mott variable range hopping model, the conductivity mechanism in the investigated samples was analyzed. The results shown that the density of states at the Fermi-level, $N(E_{F})$ is constant in the investigated temperature range and the typical values of $N(E_{F})$ are $0.713 \times 10^{18} eV^{-1} cm^{-3}$ (sample A), $0.621 \times 10^{18} eV^{-1} cm^{-3}$ (sample B) and $0.855 \times 10^{17} eV^{-1} cm^{-3}$ (sample C). Other parameters of VRH model such as the hopping distance R and the hopping energy W have also been computed and the following values at the room temperature were obtained: R=15.7 nm and W=86 meV (for sample A); R=16.3 nm and W=89 meV (for sample B) and R=26.7 nm and W=147 meV (for sample C)