RESUMEN
The synthesis of barium and strontium stannates in the process of decomposition of hydrothermally obtained precursors has been investigated. It was found that endothermic weight loss during the synthesis of barium stannate occurs in two stages, whereas during the synthesis of strontium stannate it occurs in one stage. From the summary of the results of thermogravimetric analysis, X-ray diffraction, and Mössbauer spectroscopy, the composition and local structure of X-ray amorphous phases are proposed. It is shown that the improvement of the crystal structure of the perovskite phases of MSnO3 (M = Ba, Sr) and the symmetry of the local environment of 119Sn continues up to high temperatures (1250-1500 °C) and is associated with the elimination of defects in the anion sublattice. The photocatalytic activity of hydrothermal phases MSn(OH)6 and their thermolysis products has been studied and was found not to be directly related to the specific surface area of the photocatalysts. The degradation of rhodamine B (RhB) occurs during the "dark" stages of catalysis due to the interaction of the dye with reactive oxygen species (mainly singlet oxygen). At the first stage, the decomposition of the RhB photochromic system is observed, whereas at the final stage of bleaching the dye is deethylated.
RESUMEN
In the present study, we diluted either A- or B- sublattice of perovskite multiferroic PbFe(0.5)Nb(0.5)O(3) (PFN) and studied the changes of the magnetic and ferroelectric phase transition temperatures and dielectric properties caused by such dilution. Dielectric studies of PFN single crystals show that, in contrast to the commonly adopted view, the ferroelectric phase transition in PFN is non-diffused and the relaxor-like behavior usually observed in ceramic samples has an extrinsic nature. A-site substitutions (Ba, Ca) lead to the smearing of the permittivity-temperature maximum, lowering its maximum temperature, T(m) and inducing relaxor behavior. B-site diluting of PFN by Ti increases T(m) and only slightly affects the permittivity maximum diffuseness. Both A-site and B-site substitutions in PFN lead to lowering of its Neel temperature, T(N). However, above a certain compositional threshold, fast lowering of T(N) stops and a new magnetic state with comparatively high (~50K) transition temperature becomes stable in a rather wide compositional range.
RESUMEN
Dielectric, X-ray, and piezoelectric studies of highly-resistive Li-doped (1-x)PbFe(1/2)Nb(1/2)O(3)-(x)PbTiO(3) (PFN-xPT) ceramics from the 0 ≤ x ≤ 0.2 range fabricated by solid-state synthesis and usual sintering have been carried out. Distinct anomalies of dielectric and piezoelectric parameters, corresponding to the transition between rhombohedral (monoclinic) and tetragonal ferroelectric phases, have been observed in pure PFN and PFN-xPT compositions with PbTiO(3) content up to 8 mol.%. The x,T-phase diagram of the PFN-xPT solid solution system has been constructed using these data.