The structures of the acid-paste-prepared α-form of cobalt phthalocyanine (α-PcCo) and of its corresponding β-form (β-PcCo) have been refined through X-ray powder diffraction using the Rietveld method. The α-polymorph is triclinic, space group P1̄, cell parameters a = 12.090(8) Å, b = 3.754(2) Å, c = 12.800(9) Å, α = 88.96(6)°, β = 90.97(6)°, γ = 95.09(7)°, and Z = 1; the β-form is monoclinic, space group P21/a, cell parameters a = 14.5982(9) Å, b = 4.7937(3) Å, c = 19.4348(11) Å, β = 120.782(3)°, and Z = 2. α-PcCo consists of columnarly arranged molecules, those of adjacent columns being aligned parallel to each other, whereas a nearly perpendicular arrangement is present in β-PcCo. α-PcCo also differs from the α-forms of PcH2 and PcPt in which an angle of ca. 125° is observed between molecules of closely contacting chains. From the refined peak-profile parameters of the powder pattern a crystallite size of ∼150 Å has been estimated for α-PcCo, a value approaching that of nanocompounds. The isothermal α → β phase transition has been followed in-situ real-time by means of EDXD at two different temperatures, 152 and 250 °C. Calorimetric data indicate two different behaviors of the rate constant in the temperature ranges 182.5−220 and 220−270 °C leading to values of the empirical activation energy, E a, of 36.6(16) and 14.8(9) kcal/mol, respectively. However the various DSC runs lead to values of the phenomenological n parameter in the range 2.34−2.68 (indicating an isokinetic two-dimensional growth). According to the combined EDXD and DSC data a three-step model for the α → β PcCo phase transition may be proposed:  (1) disordering of adjacent layers of PcCo molecules from their original α-type arrangement; (2) crystallization of the β-form from the disordered phase through rearrangement of the layers of the phthalocyanine units; (3) crystal growth of the β-phase from the nuclei to an average particle size of ∼ 2500 Å, as indicated by the fitted peak-profile parameters. No evidence of the occurrence of intermediate ordered phases was observed.

The temperature dependence of ethylammonium chloride structure has been investigated by in situ laboratory parallel-beam X-ray powder diffraction. A polymorphic transition from a monoclinic LT phase to a tetragonal HT phase has been observed at 358 K. Such transformation has a reconstructive character. The thermal expansion of both polymorphs is small and anisotropic as a consequence of their organization through an anisotropic interaction network. The high temperature (HT) phase (possible space group P4/n or P4/nmm, a = 5.05 Å, c = 9.99 Å) has an excess volume of ~11% as compared with the low temperature (LT) one. The HT polymorph's structure has been solved by direct methods using powder diffraction data. In the absence of clear indications, it has been refined in P4/nmm. The structural properties of an ethylammonium chloride/water mixture at ambient conditions were also studied by using an integrated approach, which combines X-ray diffraction measurements and molecular dynamics simulations carried out with both the SPC/E and TIP5P water models. By refining a single interaction potential, very good agreement between the theoretical and experimental diffraction patterns was obtained, especially in the case of the TIP5P simulation. A complex structural behavior in which cations and anions do not possess a completely closed hydration shell of their own has been highlighted. Conversely, "solvent-shared ion pairs" are formed, in which one or more water molecules act as a bridge between the chloride and ethylammonium ions. Moreover, a strong water-water correlation is found, indicating that the water molecules in the mixture tend to aggregate and form water clusters.

We present an analysis of the structure of the monomethylammonium nitrate (MMAN) compound. Vibrational Raman spectroscopy and X-ray powder diffraction have been used to characterize the bulk phases of MMAN, and assignment of the resonant frequencies has been performed by ab initio (DFT) computations on small clusters of the compound. The theoretical spectra are in excellent agreement with the experimental ones and provide a means by which an interpretation of the hydrogen-bonding network that exists in such compound can be analyzed. In particular, we found that the spectrum of one of the solid phases is structurally very similar to that of the liquid. We present experimental evidence for the existence of such phase both from X-ray data and Raman spectra which, in turn, is easily interpreted with a one-to-one correspondence with the ab initio simulation of the small clusters. A geometric structure of the short-range local arrangement in these two bulk phases is therefore proposed.

A complete crystal-chemical characterization of erionite-K from Rome, Oregon, was obtained by combining field emission scanning electron microscopy, laboratory parallel-beam transmission powder diffraction, and 57Fe Mössbauer spectroscopy. Rietveld refinement results evidenced that the most striking difference in comparison with the structure of erionite-Ca is significant K at a K2 site (1/2, 0, 0), which is empty in erionite-Ca. In addition, site Ca1 shows low occupancy and Ca3 is vacant. The oxidation and coordination state of Fe, whose occurrence was revealed by chemical analysis, have been clarified by exploiting room- and low-temperature 57Fe Mössbauer spectroscopy. The majority of Fe (95%) was attributed to Fe 3+-bearing, superparamagnetic, oxide-like nanoparticles with dimensions between 1 and 9 nm, and the remaining 5% was attributed to hematite particles with size >10 nm, both located on the crystal surface

Homogeneous maghemite (γ–Fe2O3) nanoparticles with an average crystal size around 5 nm were synthesized by successive hydrolysis, oxidation, and dehydration of tetrapyridino-ferrous chloride. Morphological, thermal, and structural properties were investigated by transmission electron microscopy (TEM), differential scanning calorimetry (DSC), and x-ray diffraction (XRD) techniques. Rietveld refinement indicated a cubic cell. The superstructure reflections, related to the ordering of cation lattice vacancies, were not detected in the diffraction pattern. Kinetics of the solid-state phase transition of nanocrystalline maghemite to hematite (α–Fe2O3), investigated by energy dispersive x-ray diffraction (EDXRD), indicates that direct transformation from nanocrystalline maghemite to microcrystalline hematite takes place during isothermal treatment at 385 °C. This temperature is lower than that observed both for microcrystalline maghemite and for nanocrystalline maghemite supported on silica.

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Thermal behaviour and kinetics of dehydration of gypsum in air have been investigated using in situ real-time laboratory parallel-beam X-ray powder diffraction data evaluated by the Rietveld method. Thermal expansion has been analysed from 298 to 373 K. The high-temperature limits for the cell edges and for the cell volume, calculated using the Einstein equation, are 4.29 x 10(-6), 4.94 x 10(-5), 2.97 x 10(-5), and 8.21 x 10(-5). Thermal expansion of gypsum is strongly anisotropic being larger along the b axis mainly due to the weakening of H2 center dot center dot center dot O1 hydrogen bond. Dehydration of gypsum has been investigated in isothermal conditions within the 348-403 K range with a temperature increase of 5 K. Dehydration proceeds through the CaSO4 center dot 2H(2)O -> CaSO4 center dot 0.5H(2)O -> gamma-CaSO4 steps. Experimental data have been fitted with the Avrami equation to calculate the empirical activation energy of the process. No change in transformation mechanism has been observed within the analysed temperature range and the corresponding E-a is 109(12) kJ/mol