39 research outputs found
Investigation of the reactivity of AlCl3 and CoCl2 toward molten alkali-metal nitrates in order to synthesize CoAl2O4
Cobalt aluminate CoAl2O4 powder, constituted of nano-sized crystallites, is prepared, involving the reactivity of AlCl3 and CoCl2 with molten alkali-metal nitrates. The reaction at 450 °C for 2 h leads to a mixture of spinel oxide Co3O4 and amorphous γ-Al2O3. It is transformed into the spinel
oxide CoAl2O4 by heating at 1000 °C. The powders are mainly characterized by XRD, FTIR, ICP, electron microscopy and diffraction, X-EDS and diffuse reflection. Their properties are compared to those of powders obtained by solid state reactions of a mechanical mixture of chlorides or oxides submitted to the same thermal treatment
Optical conductivity of the nonsuperconducting cuprate La(8-x)Sr(x)Cu(8)O(20)
La(8-x)Sr(x)Cu(8)O(20) is a non-superconducting cuprate, which exhibits a
doubling of the elementary cell along the c axis. Its optical conductivity
sigma (omega) has been first measured here, down to 20 K, in two single
crystals with x = 1.56 and x = 2.24. Along c, sigma (omega) shows, in both
samples, bands due to strongly bound charges, thus confirming that the cell
doubling is due to charge ordering. In the ab plane, in addition to the Drude
term one observes an infrared peak at 0.1 eV and a midinfrared band at 0.7 eV.
The 0.1 eV peak hardens considerably below 200 K, in correspondence of an
anomalous increase in the sample dc resistivity, in agreement with its
polaronic origin. This study allows one to establish relevant similarities and
differences with respect to the spectrum of the ab plane of the superconducting
cuprates.Comment: Revised version submitted to Phys. Rev. B, including the elimination
of Fig. 1 and changes to Figs. 4 and
Magnetic and Electrical Properties of Ordered 112-type Perovskite LnBaCoMnO5+\delta (Ln = Nd, Eu)
Investigation of the oxygen-deficient 112-type ordered oxides of the type
LnBaCoMnO5+\delta (Ln = Nd, Eu) evidences certain unusual magnetic behavior at
low temperatures, compared to the LnBaCo2O5+\delta cobaltites. One observes
that the substitution of manganese for cobalt suppresses the ferromagnetic
state and induces strong antiferromagnetic interactions. Importantly,
NdBaCoMnO5.9 depicts a clear paramagnetic to antiferromagnetic type transition
around 220 K, whereas for EuBaCoMnO5.7 one observes an unusual magnetic
behavior below 177 K which consists of ferromagnetic regions embedded in an
antiferromagnetic matrix. The existence of two sorts of crystallographic sites
for Co/Mn and their mixed valence states favor the ferromagnetic interaction
whereas antiferromagnetism originates from the Co3+-O-Co3+ and Mn4+-O-Mn4+
interactions. Unlike the parent compounds, the present Mn-substituted phases do
not exhibit prominent magnetoresistance effects in the temperature range
75-400K.Comment: 23 pages including figure
Development of nano oxide αCoMoO
Molybdates oxides as AMoO4 (A = Cu, Co), have remarkable properties. These properties depend strongly on the crystallite size. Nanostructured Powders of these molybdates make their applications more usable. The aim of our work is to synthesize oxide CoMoO4 by soft chemistry method, which has the advantage of producing very fine and homogeneous powders, which increases their reactivity. The products obtained were characterized by XRD, SEM and TEM
Development of nano oxide αCoMoO4 by soft chemistry
Molybdates oxides as AMoO4 (A = Cu, Co), have remarkable properties. These properties depend strongly on the crystallite size. Nanostructured Powders of these molybdates make their applications more usable. The aim of our work is to synthesize oxide CoMoO4 by soft chemistry method, which has the advantage of producing very fine and homogeneous powders, which increases their reactivity. The products obtained were characterized by XRD, SEM and TEM