Search

Abstract: In the present paper we report the combustive synthesis of a series of polycrystalline compounds with the general formula Pb1.33Sr0.67−x Ba x Fe2O5 (0≤ x ≤0.67). They belong to a new class of materials derived from perovskite by crystallographic shear planes, which changes the iron coordination from corner-shared octahedra to edge-shared trigonal bipyramids at the shear planes. These materials are considered to be prospective candidates for multiferroics. The samples were characterized by thermal analysis (TG-DTA), X-ray diffraction and scanning electron microscopy. The crystal structure parameters were refined using the TOPAS 3 program. The observed structural changes were related to the substitution of Sr2+ by Ba2+ within a limited part of the structure. It may be concluded that the “inflation” of the perovskite blocks provoke corresponding changes within the double-chain layers. As a result, the structure appears to be very flexible and adaptive towards cation substitutions. [Copyright &y& Elsevier]

Abstract: The synthesis of polycrystalline materials as well as the conditions for single crystals growth of solid solution compounds with general formula Al2−x In x (WO4)3 have been investigated and optimized. The solid solutions structure and the changes in the lattice parameters corresponding to the indium concentration in the materials have been established. The single crystals growth has shown that the indium effective distribution coefficients depend on the initial indium concentration and they strongly differ from unity. [Copyright &y& Elsevier]

BiFeO3 is an interesting material due to its multiferroic properties. It attracts attention due to its potential applications in spintronics and in microelectronics for data storage, among others. Single-phase bulk material from BiFeO3 is difficult to synthesize. The kinetics of perovskite phase formation most often leads to the presence of impurity phases. It has been shown that low levels of replacement of Bi with rare earth ions lead to stabilization of the perovskite phase. In the present work, Rietveld refinement of the crystal structure based on powder X-ray diffraction patterns was applied to study the influence of partial substitution of Bi by rare-earth (RE) elements with different ionic radii on structural and morphological properties of the ferrite phase. Substitution by large RE ions was found to preserve the rhombohedral symmetry of BiFeO3, whereas substitution by smaller RE ions led to the coexistence of two polymorphic perovskite phases with rhombohedral R3c and orthorhombic Pnma symmetries. The unit cell parameters as well as the interatomic distances and angles, not only around the A cation but also around the iron ions, were influenced by the substitution. The mean crystallite and particle size decreased with the decrease of ionic radius of substituting RE ion. [ABSTRACT FROM AUTHOR]

The synthesis of guanidinium lead iodide, C(NH 2) 3 PbI 3 (GUAPbI 3), was conducted by slow evaporation of the mixture obtained by dissolving PbI 2 and C(NH 2) 3 I in acetonitrile. When the evaporation is done at 40 ºC, a yellow needle-like crystals are being formed. The sample was characterized by elemental analysis, density measurements, scanning electron microscopy, thermal analyses, high-temperature X-ray powder diffraction and infrared spectroscopy measurements. The elemental analysis of the obtained crystals confirmed the proposed stoichiometry. The performed thermal analyses showed an endothermic peak associated with structural transition around 160 ºC. On the other hand, the endothermic temperature effects above 300 ºC are accompanied with mass loss and were interpreted as compound degradation. The crystal structure of high temperature polymorph between 160 ºC and 300 ºC was determined using high-temperature powder diffraction data measurements at 280 ºC using simulated annealing technique in order to obtain initial structural model. The structure was refined using the Rietveld method. At temperatures higher than 160 ºC, C(NH 2) 3 PbI 3 crystallizes in hexagonal space group P 6 3 mc with unit cell parameter a increasing from 9.269 Å to 9.337 Å between 160 ºC and 300 ºC and c parameter increasing from 15.211 Å to 15.287 Å in the same temperature range. The structure consists of PbI 6 octahedra couples sharing a common face, linked with corners. Guanidinium cations are situated in the channels between Pb 2 I 9 couples in a manner that the plane of the molecule is perpendicular to the c- axis. ga1 • High temperature (HT) crystal structure of C(NH 2) 3 PbI 3 (>160 °C) is hexagonal, P6 3 mc. • In HT-structure face sharing Pb 2 I 9 polyhedra are linked with corners. • The HT-phase show stronger hydrogen bonding and more symmetrical GUA+ ion, compared to the RT-phase. • During the thermal degradation, CH 3 I, NH 3 and N 2 are released as gases and PbI 2 as a solid product. [ABSTRACT FROM AUTHOR]