Evaluation of manganese and oxygen content in La0.7Sr0.3MnO3−δ and correlation with the thermodynamic data

In order to understand how the thermodynamic properties are related to the oxygen and manganese content in the Sr-doped lanthanum manganites, nonstoichiometric perovskite phases La_0.7Sr_0.3MnO_3−δ have been investigated by using solid state electrochemical techniques, as well as wet chemical methods. The influence of the oxygen stoichiometry change on the thermodynamic properties was examined using the data obtained by a coulometric titration technique coupled with solid state electromotive force measurements (EMF). The results were correlated with the average Mn valence values as determined by a chemical method based on two independent iodometric titrations, with amperometric dead-stop end point detection. New features related to the relationship between the average Mn valence, the oxygen nonstoichiometry variation, and the thermodynamic behavior were evidenced.     

Spectral, magnetic and thermal characterisation of new Co(II), Ni(II) and Cu(II) complexes with Schiff base 5-bromo-N,N′-bis-(salicylidene)-o-tolidine

Starting from 5-bromo-N,N′-bis-(salicylidene)-o-tolidine (H₂L) new complexes with Co(II), Ni(II) and Cu(II) were synthesised and characterised. The features of complexes have been assigned from microanalytical, IR, UV–Vis–NIR and EPR spectra, magnetic data at room temperature as well as thermal analysis. IR data are in accordance with bischelate nature of the deprotonated ligand that coordinates through azomethinic nitrogen and phenolic oxygen. The electronic spectra display the characteristic pattern of tetrahedral stereochemistry for [CoL]·H₂O complex and octahedral one for [NiL(OH₂)₂]·H₂O complex. The electronic spectra correlated with magnetic susceptibility measurements indicate a square-planar surrounding for [ML] (M:Ni, Cu) species, while the EPR spectrum of copper complex sustains the proposed stereochemistry. The thermal analysis evidenced that thermal transformations are complex processes according to TG, DTA and DTG curves including (crystallization or coordination) water elimination, thermolyses and oxidative degradation of Schiff base. All these processes lead to the most stable metallic oxides as final product.     

Crystallization study of sol-gel un-doped and Pd-doped TiO2 materials

Sol-gel nanostructured titania materials have been reported to have applications in areas ranging from optics via solar energy to gas sensors. In order to enhance the photocatalytic activity, there are many studies regarding the doping of titanium dioxide (TiO₂) material with either non-metals (S, C, N, P) or metals (Ag, Pt, Nd, Fe). The present work has studied some un-doped and Pd-doped sol-gel TiO₂ materials (films and gels), with various surface morphologies and structures, obtained by simultaneous gelation of both precursors Ti(OEt)₄ and Pd(acac)₂. Their structural evaluation and crystallization behavior with thermal treatment were followed by DTA/TG analysis, infrared (IR) spectroscopy, Fourier transform infrared (FTIR), spectroellipsometry (SE), X-ray diffraction (XRD) and atomic force microscope (AFM). The influence of Pd on TiO₂ crystallization for both supported and un-supported materials was studied (lattice parameters, crystallite sizes, internal microstrains). The changes in the optical properties of the TiO₂-based vitreous materials were correlated with the changes of the structure. The hydrophilic properties of the films were also connected with their structure, composition and surface morphology.