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