The silver (Ag) powder was synthesized in a mechanochemical (MC) process by inducing a solid-state displacement reaction between silver chloride (AgCl) and copper (Cu). This process was carried out in argon atmosphere conditions using a planetary ball mill. The reaction caused the mixture of AgCl and Cu to change the composition of the mixture to Ag and copper chloride (CuCl). CuCl was separated from MC product by leaching with ammonium hydroxide. Thus, Ag powder was obtained as the final product. Stearic acid (C18H36O2) was used as the additive to improve dispersion of Ag powder during the MC process. The ground powders, formed in the presence and absence of additive, were characterized by X-ray diffraction (XRD) and scanning electron microscope (SEM). The XRD determined that the reaction between AgCl and Cu was completed in 18 h milling. SEM and particle size analysis examinations revealed that the size of the particles in the synthesized metallic Ag powder was in the range of 30–300 nm.

The paper describes an approach for automated crystal structure solution from powder diffraction data using the multi-population genetic algorithm (MPGA). The advantage of using co-evolution with the best individual exchange, compared with the using of the evolution with a single genetic algorithm without interpopulation exchange, is shown. As an example, the paper describes the use of MPGA for solving the [Pt(NH3)5Cl]Br3 crystal structure, having the tetragonal I41/a space group [a = 17.2587(5) Å, c = 15.1164(3) Å, Z = 16, unit-cell volume V = 4502.61(10) Å3]. The MPGA convergence charts and the atomic positions distribution maps of the MPGA populations are given. The description of the final structure solution is also shown.

Two examples of anionic complexes having vapochromic behavior are investigated: [K(H2O)][Pt(ppy)(CN)2] “Pt(ppy)” and [K(H2O)][Pt(bzq)(CN)2] “Pt(bzq)”, where ppy = 2-phenylpyridinate and bzq = 7,8-benzoquinolate. These monohydrate-potassium salts exhibit a change in color from purple to yellow [Pt(ppy)] and from red to yellow [Pt(bzq)] upon heating to 110 °C, and they transform back into the original color upon absorption of water molecules from the environment. Available only in the form of polycrystalline samples, no structural information on such compounds is accessible, due to highly overlapping peaks in powder diffraction profiles. We use in situ Pair Distribution Function measurements on powder samples to investigate the dynamics of the structural changes induced by temperature variations. By means of a multivariate approach, we were able to extract dynamic structural information from collected profiles without using prior knowledge on the static crystal structure of the compounds. The critical temperature and the characteristics of the vapochromic transition have been identified, as well as the main structural changes causing it.

A combination of neutron diffraction, synchrotron X-ray diffraction, and high-resolution extended X-ray absorption fine structure measurements has been used to clarify the correlations between long- and local-range structural distortions across the spin-state transition in powders of LaCoO3 and La0.5Sr0.5Co0.75Nb0.25O3. The analysis of the diffraction data has revealed that the isotropic thermal parameters of Co–O bond abnormally increase below 100 K in both samples, while the temperature dependence of the average Co–O bond lengths is linear from 10 to 300 K. We also have found that the Co–O bond lengths are larger in La0.5Sr0.5Co0.75Nb0.25O3, as compared with the ones in LaCoO3. The X-ray absorption data showed an anomalous decrease of the Co–O bond lengths only for LaCoO3, in contrast to the bond length values obtained by diffraction. The structural anomalies observed by spectroscopy measurements are discussed in terms of the spin-state transition model.

A combined X-ray powder diffraction (XPD) and high-resolution extended X-ray absorption fine structure (EXAFS) at the Co and Ga K-edges study has been performed for LaCoO3 and LaGaO3 ceramics, the latter sample was used as a reference without spin transitions. Based on the X-ray diffraction data, we have found that isotropic atomic displacement parameters (ADP) or mean-squared displacement of the Co–O bond exhibit gradual growth below ~50 K, wherein the strain dependencies testify rapid increase below 150 K for the LaCoO3 having rhombohedral structure. No similar features could be observed for LaGaO3 sample. Above ~100 K the isotropic ADP of the Co–O bond indicate a gradual growth, whereas strain curves show distinct bend near the spin-state transition temperature at about 150 K. According to the EXAFS data, the correlated parallel mean squared relative displacement (MSRD||) of Co–O and Ga–O bonds exhibit a gradual growth above 150 K; however, in the LaCoO3 this parameter is notably bigger. It is supposed that at low temperature the cobalt ions are dominantly in low-spin (LS) state, while certain amount of Co3+ ions located within the surface layer of the crystallines have high-spin state (HS). Temperature growth leads to a gradual transformation of the HS state of the cobalt ions into the highly-hybridized intermediate-spin (IS) state, while the cobalt ions located in the inner part of the crystallines remain LS configuration up to 150 K. Further temperature increase leads to a spin transition of the Co3+ ions located within the crystallines from the LS state into the IS one.

Computational methods and a program to obtain crystal structures that have the perfectly identical diffraction patterns, i.e. structure factors with the same absolute values and the same lattice symmetry are discussed. This is directly related to the uniqueness of solutions in crystal structure determination of single-crystal/powder-crystal samples from diffraction data. In order to solve the problem, it is necessary to solve a system of quadratic equations. The framework of positive-semidefinite programming is used herein to solve the system efficiently.

An organic polar hydrate was obtained through cocrystallization of 2,4-diaminotoluene (2,4-DAT) and L(+)-tartaric acid (TA) from ethanol. Dehydration behavior of the obtained hydrate was investigated using variable temperature powder X-ray diffraction (PXRD) and thermal analysis. Proton transfer from L(+)-TA to 2,4-DAT in both hydrate and dehydrated form was revealed via Fourier transform infrared spectroscopy. The crystal structures of both forms were determined using PXRD techniques. The similarities and differences between two crystal structures were analyzed and the role of water in the hydrate crystal structure was demonstrated.