Thermal study of CoxZn7-xSb2O12 spinel obtained by pechini method using different alcohols

With the aim of obtaining materials with applications in pigments, Co_xZn_7-xSb₂O₁₂ spinels were synthesized using the Pechini method. This method consists in the formation of a polymeric net, where the metallic cations are homogeneously distributed. In this work, two types of alcohol (ethyl glycol and ethylene glycol) were used for the synthesis of a zinc antimoniate spinel, Co_xZn_7-xSb₂O₁₂ (x=0-7). The materials were characterized by termogravimetry (TG) and differential thermal analysis (DTA). TG results indicated a decrease in total mass loss when cobalt was added to the solution substituting zinc, for samples prepared using the two different alcohols. Decomposition temperatures, obtained by TG and DTA, presented a decreasing behavior as cobalt was added to the material. In relation to the alcohols, all results indicated a better polymerization of the resin when ethylene glycol was used, being the most indicated one for cation immobilization. X-ray diffraction did not show differences between the two alcohols - both presented the spinel phase (Co, Zn)_2.33Sb₀.₆₇O₄. Samples with higher quantity of cobalt also presented ilmenite phase (Co, Zn)Sb₂O₆. This revised version was published online in August 2006 with corrections to the Cover Date.     

Structural Analysis of Ti And Pb Citrate Using NMR and FT-Raman Signals and Quantum Mechanics Simulations

Titanium citrate and lead and titanium citrate were prepared by polymeric precursor method in aqueous solution. This citrate was analyzed by ¹H, ¹³C NMR and gHMBC–NMR (Hetero-nuclear multiple-bond correlation) to investigate the formation of the citrate complexs and influence of the Pb²⁺ ion in this complex. These complexs were characterized by interaction between Ti⁴⁺ ion and citric acid carboxyls. Quantum mechanic simulations in level ab initio were used to study the electronic structure and natural charges (NBO) to both the complexs. Such techniques indicated the formation of an octahedral complex with an arrangement similar to Ti atom in the crystalline structure of the PbTiO₃. A study using the technique FT-Raman made possible the confirmation of the interaction among the Ti⁴⁺ and Pb²⁺ ions with the citric acid carboxyls.     

Rapid calcination of ferrite Ni0.75Zn0.25Fe2O4 by microwave energy

Ferrites Ni_0.75Zn_0.25Fe₂O₄ were obtained by polymeric precursor method and calcined in a short time with microwave energy to assess the morphological and microstructural characteristics. Samples were calcined at 500, 650, 800, and 950 °C for 30 min in a microwave oven. The resulting powders were characterized by thermal analysis (TG/DSC), X-ray diffraction (XRD), Fourier transform infrared spectrometer, field-emission gun scanning electron microscope (FEG-SEM), and energy-dispersive X-ray spectroscopy. The XRD results showed the formation of single ferrite phase at temperature of 500 °C for 30 min. The FEG-SEM analysis showed agglomerated particles with formation of non-dense longitudinal plates, with interparticle porosity and agglomerated fine particles. The rapid calcination by microwave energy demonstrated satisfactory results in relatively low temperature of 500 °C for 30 min and appeared to be a promising technique for obtaining nickel–zinc ferrite powders.     

Photoluminescence in the CaxSr1−xWO4 system at room temperature

In this work, a study was undertaken about the structural and photoluminescent properties, at room temperature, of powder samples from the Ca_xSr_1−xWO₄ (x=0-1.0) system, synthesized by a soft chemical method and heat treated between 400 and 700 °C. The material was characterized using Infrared, UV-vis and Raman spectroscopy and XRD. The most intense PL emission was obtained for the sample calcined at 600 °C, which is neither highly disordered (400-500 °C), nor completely ordered (700 °C). Corroborating the role of disorder in the PL phenomenon, the most intense PL response was not observed for pure CaWO₄ or SrWO₄, but for Ca_0.6Sr_0.4WO₄. The PL emission spectra could be separated into two Gaussian curves. The lower wavelength peak is placed around 530 nm, and the higher wavelength peak at about 690 nm. Similar results were reported in the literature for both CaWO₄ and SrWO₄.     

Effect of the modifier ion on the properties of MgFe<Subscript>2</Subscript>O<Subscript>4</Subscript> and ZnFe<Subscript>2</Subscript>O<Subscript>4</Subscript> pigments

Magnesium and zinc ferrites have been prepared by the polymeric precursor method. The organic material decomposition was studied by thermogravimetry (TG) and differential thermal analysis (DTA). The variation of crystalline phases and particle morphology with calcination temperature were investigated using X-ray diffraction (XRD) and scanning electronic microscopy (SEM), respectively. The colors of the ferrites were evaluated using colorimetry. Magnesium ferrite crystallizes above 800°C, presenting a yellow- orange color with a reflectance peak at the 600–650 nm range, while zinc ferrite crystallizes at 600°C, with a reflectance peak between 650–700 nm, corresponding to the red-brick color.     

Magnetic Behavior at Low Temperatures of Ti Oxide Polycrystalline Samples

Ti-oxide polycrystalline samples have been synthesized by the Pechini method and their low temperature magnetic properties have been characterized. The synthesis procedures allow the preparation of high-quality samples ensuring that the observed low temperature magnetic behavior is intrinsic to the system, not due to the polycrystalline nature of the samples. Magnetic susceptibility measurements showed that the anatase and rutile TiO₂ exhibit a paramagnetic behavior. For the CoTiO₃ samples, a totally reversible antiferromagnetic transition at 38 K is reported.     

A novel approach for the development of photoluminescent material

We report on several amorphous compounds based on different metal oxianions with intense photoluminescence at room temperature. These compounds were synthesised by a soft chemical process and deposited on Si (100) by a spin-coating technique. To select these different metal oxianions, a classic concept based on a metal oxide network former is used. We describe a minimum set of requirements to obtain an amorphous metal oxide with photoluminescence emission at room temperature. Received: 27 August 2001 / Accepted: 29 August 2001 / Published online: 20 December 2001     

Photoluminescence in amorphous zirconium titanate

Photoluminescence at room temperature was observed in amorphous zirconium titanate obtained from the polymeric precursor method. This was the first time in which PL was noticed in an amorphous compound made of two network formers. The PL spectra could be deconvoluted into two bands, whose center 1 was located from 540 nm to 552 nm and center 2 from 625 nm to 641 nm. The co-existence of fivefold and sixfold oxygen coordination of titanium and/or zirconium could be the origin of the radiative recombination of electron-hole pairs in amorphous ZT, which may be responsible for the emission of the photoluminescence. PACS 78.55.m; 78.55.Hx; 78.66.W; 78.66.Jg; 81.20.Fw     

Structural and thermal characterization of Zn2−xCoxTiO4

In this work, spinels with the general formula Zn_2?xCo_xTiO₄ were synthesized by the polymeric precursor method and thermally treated at 1,000 °C. The powder precursors were characterized by TG/DTA. A decrease in the DTA peak temperature with the amount of zinc was observed. After the thermal treatment, the characterizations were performed by XRD, IR, colorimetry and UV/VIS spectroscopy. The XRD patterns of all the samples showed the presence of the spinel phase. Infrared spectroscopy showed the presence of ester complexes for Zn₂TiO₄ after thermal treatment at 500 °C, which disappeared after cobalt addition, indicating that organic material elimination was favored.