Search

Electrical and electrocatalytic properties of two series of double perovskites, LnCo1-xCrxO3 (Ln = Pr, Gd, and x = 0, 0.5 and 1), were investigated and discussed in the light of perovskite composition. Studied perovskites were synthesized by the solution combustion method, and powder XRD patterns showed that all compounds crystallize in the GdFeO3-structure type. The morphology of perovskite crystals was studied by SEM, whereas obtained microphotographs implied porous microstructure. The conductivity of both perovskite series spanned in the range of semiconductors as revealed from electrical measurements. The electrocatalytic activity toward oxygen evolution reaction, oxidation of hydrogen peroxide, and methanol was studied in alkaline solutions by cyclic voltammetry. The influence of electronic, structural and morphological factors to the electrical and electrocatalytic properties is discussed. The praseodymium series showed higher electrocatalytic activity than the gadolinium one, while the most pronounced activity was detected for PrCoO3. [ABSTRACT FROM AUTHOR]

The results on synthesis, crystal structure determination and calculation of crystallochemical parameters of YCoFeO ( x = 0, 0.33, 0.5, 0.67 and 1) perovskites are presented in this work. The compounds within this series were synthesized by solution combustion method using two different fuels: urea and citric acid. It was found that iron-containing perovskites, obtained by citric acid as a fuel are of better quality and crystallinity. All the compounds crystallize in Pnma space group with Z= 4. According to the structure and the calculated crystallochemical parameters, the coordination number of Y in these perovskites is 8. The unit cell parameter relationship is of O−type suggesting that the main reason for distortion of ideal perovskite structure is the octahedral tilting. The deformation of the octahedrons, as well as the tilting angles, are increasing with the increasing content of Fe but the calculated global instability indices ( GII) show that the stability of the perovskite structure is increasing with increasing of the Fe content. [Figure not available: see fulltext.] [ABSTRACT FROM AUTHOR]

The title compounds are prepared by a solution combustion method from solutions of Y(NO3)3, Co(NO3)2, and Fe(NO3)3 in a small amount of water. [ABSTRACT FROM AUTHOR]

The appearance and formation of an isosbestic point in the temperature-dependent IR spectra can be used to reveal a phase transition at a certain temperature. This conclusion was made by a thorough investigation of the IR (transmission and ATR) spectra of methylammonium iodide (MAI) and formamidinium iodide (FAI) recorded in a wide temperature range starting from -170 to +200 °C. By investigating the isosbestic points, it was found that MAI undergoes two phase transitions at -110 and +146 °C. The results obtained for FAI also showed two phase transitions at 73 and 115 °C. Furthermore, it was found that the shift of certain bands that are provoked by the phase change could be used to calculate the transition temperature. So far, according to the literature data, no attempts have been made to reveal the exact temperature of phase transitions using IR spectroscopic techniques., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2020. Published by Elsevier B.V.)

In this work supervised self-organizing maps were used for structural classification of perovskites. For this purpose, structural data for total number of 286 perovskites, belonging to ABO3 and/or A2BB'O6 types, were collected from literature: 130 of these are cubic, 85 orthorhombic and 71 monoclinic. For classification purposes, the effective ionic radii of the cations, electronegativities of the cations in B-position, as well as, the oxidation states of these cations, were used as input variables. The parameters of the developed models, as well as, the most suitable variables for classification purposes were selected using genetic algorithms. Two-third of all the compounds were used in the training phase. During the optimization process the performances of the models were checked using cross-validation leave-1/10-out. The performances of obtained solutions were checked using the test set composed of the remaining one-third of the compounds. The obtained models for classification of these three classes of perovskite compounds show very good results. Namely, the classification of the compounds in the test set resulted in small number of discrepancies (4.2-6.4%) between the actual crystallographic class and the one predicted by the models. All these results are strong arguments for the validity of supervised self-organizing maps for performing such types of classification. Therefore, the proposed procedure could be successfully used for crystallographic classification of perovskites in one of these three classes.

The crystal structures at room (296 K) and low (173 K) temperature of several alpha-alums have been refined by single-crystal X-ray structure analysis. Many alpha-alums of known structure are disordered, the sulfate anions occupying one of two possible sites. All those studied here exhibited such disorder and the relative occupancies of the two sites are in excellent agreement with those obtained by Raman spectroscopy, where the nu1(SO4) mode is seen as a doublet owing to the presence of two different types of sulfate ion. No phase transitions were noted on cooling but there is less disorder.