Thermal Decomposition Of Citrate Precursor Research Articles

Suppression of Ru (S = 1) spin dimerization in La2RuO5 by Ti substitution

La2RuO5 shows a magneto-structural phase transition at 161 K with spin dimerization and concomitant formation of a non-magnetic singlet ground state. To gain a deeper insight into the origin of this transition systematic substitution of Ru by Ti has been carried out. Polycrystalline samples have been synthesized by thermal decomposition of citrate precursors leading to La2Ru1−yTiyO5 (0 ≤ y ≤ 0.45). The crystal structure was investigated by x-ray powder diffraction at room temperature and at 100 K. The valences of Ti and Ru were obtained from x-ray absorption near edge structure spectroscopy at the Ti–K and the Ru–LIII absorption edges, respectively. The magnetic phase transition was investigated by magnetic susceptibility measurements as a function of Ti substitution, revealing a decreasing transition temperature on increasing the level of substitution. The step-like feature in the magnetic susceptibility reflecting the Ru–Ru spin dimerization transition becomes smeared out close to y = 0.3 and completely vanishes at y = 0.45, indicating complete suppression of spin-dimer formation. Additional specific-heat measurements show a continuous decrease of the magnetic entropy peak with increasing Ti substitution mirroring the reduced number of spin dimers due to the magnetic dilution. A magnetic anomaly of the dimerization transition can hardly be detected for y ≥ 0.3. Density functional theory calculations were carried out to study changes of the electronic band structure caused by the substitution. A possibly preferred distribution of Ti and Ru and the magnetic interactions as well as the change of the density of states close to the Fermi level are investigated. Based on these experimental results a detailed (y,T) phase diagram is proposed.

Synthesis of thin-multiwalled carbon nanotubes by Fe-Mo/MgO catalyst using sol-gel method

The sol-gel technique has been studied to fabricate a homogeneous Fe-Mo/MgO catalyst. Ambient effects (air, Ar, and H2) on thermal decomposition of the citrate precursor have been systematically investigated to fabricate an Fe-Mo/MgO catalyst. Severe agglomeration of metal catalyst was observed under thermal decomposition of citrate precursor in air atmosphere. Ar/H2 atmosphere effectively restricted agglomeration of bimetallic catalyst and formation of highly-dispersed Fe-Mo/MgO catalyst with high specific surface-area due to the formation of Fe-Mo nanoclusters within MgO support. High-quality thin-multiwalled carbon nanotubes (t-MWCNTs) with uniform diameters were achieved on a large scale by catalytic decomposition of methane over Fe-Mo/MgO catalyst prepared under Ar-atmosphere. The produced t-MWCNTs had outer diameters in the range of 4-8 nm (average diameter ~6.6 nm) and wall numbers in the range of 4-7 graphenes. The as-synthesized t-MWCNTs showed product yields over 450% relative to the utilized Fe-Mo/MgO catalyst, and indicated a purity of about 85%.

Synthesis of ultradisperse NiFe 2O 4 spinel by thermal decomposition of citrate precursors and its magnetic properties

Peculiarities of synthesis of nanocrystalline NiFe 2O 4 powders by thermal decomposition of citrate precursors were investigated. It was found that the parameters of nanopowders are determined by the decomposition temperature and pH of the precursor media. The temperature and duration of the process of precursor decomposition are limiting factors for decrease of the grain size. An optimum relation between the limiting factors can be determined experimentally by variation of pH. Correlation between the synthesis parameters, particle size, and magnetic properties is discussed. It is shown that optimum magnetic and magnetostrictive properties were found for the bulk polycrystalline samples sintered using the powders obtained for pH 2.

L<sub>3x</sub>La<sub>2/3-X</sub>TiO<sub>3</sub> Nanoparticles Obtained from a Low Temperature Synthesis Route

In this work, the synthesis of Li3xLa2/3-xTiO3 oxide is studied by thermal decomposition of citrate precursor at very low temperature which has not been yet reported in the literature for these compounds. The characterization of oxides and its precursor was realized by DRX, IR, ATD and TEM techniques. The results show the formation of a new chemical compound (precursor) as well as several advantages of the citrate method in relation to reported ones in the literature: the ostensible decreasing of temperature Li3xLa2/3-xTiO3 formation and the decreasing of particle size on the nanometric scale which is very desirable for the electrochemical application.

Spray pyrolytic deposition of barium hexaferrite thin films for magnetic recording applications

Barium hexaferrite films with particles in the 50–80 nm size range have been prepared by a simple spray pyrolytic method starting from a citrate complex precursor. High nucleation rates during thermal decomposition of citrate precursor along with low growth rates ensure the formation of nanoparticles. The particles have a predominantly perpendicular easy-axis orientation and a perpendicular coercivity of 5000 Oe. The angular-dependent coercivity measurements show a nearly monotonic angular dependence indicating weaker grain interaction and low media noise in these films, an extremely useful property for application in high-density recording media.

Physico-Chemical Characterization of Na3Zr2Si2PO12 Fine Powders Prepared by Sol-Gel Method Using Citrates

Sodium superionic conductor (NASICON) powders have been prepared by sol-gel technique using citrates. The optimum pH condition (\\cong6) for sol-gel process was predicted by theoretical consideration of thermodynamic equilibrium constants for corresponding metal salts in aqueous solution. The pure NASICON phase with rhombohedral unit cell could be obtained by thermal decomposition of citrate precursors at a relatively low temperature (850°C). When the calcining temperature was raised to 1100°C, however, slight monoclinic distortion with formation of a trace of monoclinic ZrO2 was observed. Thermogravimetry-differential thermal analysis (TG-DTA), X-ray diffraction (XRD), Brunauer-Emmett-Teller (BET) technique, scanning electron microscopy (SEM) and 31P static and magic angle spinning (MAS) NMR have been used to characterize the calcined powders.

Spectrochemical investigations of ultrafine amorphous and crystalline rare earth iron garnets

The absorption bands caused by the lattice vibrations and electronic transitions due to tetrahedral and octahedral Fe 3+ in ultrafine submicron-sized rare earth iron garnets (RIG) prepared by the thermal decomposition of citrate precursors are studied to elucidate the local molecular structure. The ultrafine garnet samples consisting of 1.0- to 1.5-nm sized crystallites are X-ray amorphous and show evidence for greater specific volume compared to crystalline garnets in XRD and IR studies. An energy level scheme of 3 d 5 for Fe 3+ in tetrahedral and octahedral coordination in these ultrafine crystallites is proposed. The ligand-field parameters suggest a decrease of octahedral Fe O distance and an increase of tetrahedral Fe O distance. The Mo¨ssbauer isomer shift values show interesting correlations with Racah parameters and confirm the variation of Fe O distances in the amorphous state. The ultrafine crystalline materials comprising 10- to 35-nm sized crystallites exhibit absorption frequencies and ligand-field parameters comparable to crystalline garnets.

Magnetization and magnetic resonance studies of ultrafine Ho 3Fe 5O 12 and Yb 3Fe 5O 12

Ultrafine particles of Ho 3Fe 5O 12 and Yb 3Fe 5O 12 garnet materials from 1.0 to 35 nm crystalline in size are prepared by thermal decomposition of citrate precursors. The crystallites in the 1.0 to 1.5 nm size range exist in the disordered state as aggregates and exhibit superparamagnetism, whereas 10 to 35 nm crystallites are monoliths. The observed higher M s-values and T c-values of 1.0 to 1.5 nm crystallites are attributed to the weakening of the anisotropic R c 3+O 2Fe d 3+ coupling in the disordered state which allows the Fe sublattice magnetization to dominate. The g eff-values of > 2.0 in resonance studies and their inverse temperature dependence are the result of the low Ho 3+ and Yb 3+ sublattice magnetization, the presence of an internal magnetic field produced by interparticle dipolar interactions and the distortion of Fe 3+ sites in the garnet structure. The 10 to 35 nm crystallites have larger g eff-values, as compared to single crystal or polycrystalline garnets due to the dipolar interactions; the temperature dependence of g eff-values is comparable to the polycrystalline materials. The resonance line broadening in 1.0 to 1.5 nm crystallites is dominated by dipolar broadening Δ H dp whereas in 10 to 35 nm crystallites anisotropy broadening Δ H a and intrinsic broadening Δ H i are predominant.