[en] The traditional analysis of electric quadrupole interaction in disordered materials can give hyperfine parameters that would mask the actual values. As the relative distribution width δ increases, the correlation of this parameter with the rest produces strong shifts in all of them. Motivated by the values δ ≥ 0.4 fitted in BaTi_1-xHf_xO₃ for 0 ≤ x ≤ 0.2 and other perovskites we extend previous calculations for Gaussian distribution function to the interval 0.3 ≤ δ ≤ 1. We also include the study of correlation between quadrupole parameters for Lorentzian distribution function in the 0 ≤ δ ≤ 1 interval

[en] The X-ray absorption jump ratio of erbium was measured with a high resolution intrinsic germanium detector by attenuation, with an erbium foi, of a Compton peak produced by the scattering of the 60 keV americium 241 X-rays. Data analysis consists of a deconvolution to find the true Compton peak shape and an integration of a parameterized expression of the attenuation coefficient adjusted by least squares. Our result has an error of 1.5% and compared with calculated data shows a difference of less than 5%. PACS number(s): 32.80 Fb, 32.80 Cy. (author)

[en] The pressure-induced sequence of phase transitions of the BaF₂ fluorite was studied within the shell-model approach. This fluorite crystal presents two pressure-induced phase transitions at approximately 3 and 15 GPa. The interatomic potentials were calculated by using relevant physical properties measured at ambient conditions. These potentials were used to minimize the lattice enthalpy at high hydrostatic pressures. By comparing the enthalpies and lattice parameters of the three possible structures, it was possible to describe the complete phase transition sequence of the material. The model reliability is confirmed by a comparison with experimental results reported at ambient conditions, which are in good agreement with the model predictions. (author)

[en] Complete text of publication follows. Solids provide a convenient form to deliver active pharmaceutical ingredients (APIs) as part of a formulated product. However, pharmaceuticals may exist in numerous solid forms, which may feature different physical and chemical properties. These solid forms include 'true' polymorphs, solvates (pseudopolymorphs), co-crystals and amorphous solids. Polymorphism is often characterized as the ability of a drug substance to exist as two or more crystalline phases that have different arrangements and/or conformations of the molecules in the crystal lattice. Solvates and co-crystals are multicomponent systems that may be formally defined based on the state of the isolated pure components: if one component is a liquid at room temperature, the crystals are designated as solvates; if both components are solids at room temperature, the crystals are designated as co-crystals. The different structural arrangements of the APIs lead to by changes in the physical and chemical properties (e.g. thermodynamic, spectroscopic, kinetic, interfacial, mechanical, etc.), which may induce differences in manufacturability, solubility, bioavailability and stability between the different solid forms. Understanding and controlling the solid-state chemistry of APIs, both as pure drug substances and in formulated products, is therefore an important aspect of the drug development and formulation processes and has a direct impact on the quality as well as the protection of the intellectual property against possible patentrelated infringements. In order to obtain an accurate description of the solid forms of an API, analytical techniques sensitive to the crystalline structure must be applied. In principle, single crystal X-ray diffraction is the most effective technique since it directly determines the packing, conformation and intermolecular interaction of molecules. However, due to the problems associated with obtaining good quality single crystals, and the need of reliable routine analytical methods (sometimes suitable as on-line monitoring tools), the use of vibrational spectroscopy in this field is gaining increasing attention. Differently to X-ray diffraction techniques, which are sensitive to the long-range order, vibrational spectroscopy (mid-infrared, near-infrared and Raman scattering) is primarily sensitive to the short-range structure of molecular solids. Both Raman and infrared spectroscopies provide information on the structure, configuration and conformation in the solid state by probing the vibrations of atoms. Qualitative as well as quantitative analysis can be performed with both techniques. In this presentation, we will review the main applications of the vibrational spectroscopy techniques in the characterization of the solid forms of pharmaceutical substances. Specific examples of qualitative and quantitative investigations of raw materials and formulated products will be discussed and correlated with the results of other experimental techniques and quantum mechanical calculations.

[en] The crystalline structure of NaCaMg₂F₇ was determined using single crystal X-ray diffraction. This compound crystallizes in the cubic pyrochlore structure, i.e., space group Fd3-barm, lattice parameter: a=10.2610(5) A and Z=8. All atoms occupy special crystalline sites, but Na and Ca are randomly distributed in the anti-cristobalite sub-lattice of the pyrochlore structure. The vibrational spectrum was determined by polarized Raman scattering and infrared reflectance. The number of observed Raman and infrared active phonons is larger than that predicted by the factor group analysis of the pyrochlore structure. The anomalous vibrational spectrum is discussed in terms of a disorder-induced symmetry lowering mechanism

[en] Full text: Solids provide a convenient form to deliver active pharmaceutical ingredients (APIs) as part of a formulated product. However, pharmaceuticals may exist in numerous solid forms, which may feature different physical and chemical properties. These solid forms include 'true' polymorphs, solvates (pseudopolymorphs), co-crystals and amorphous solids. Polymorphism is often characterized as the ability of a drug substance to exist as two or more crystalline phases that have different arrangements and/or conformations of the molecules in the crystal lattice. Solvates and co-crystals are multicomponent systems that may be formally defined based on the state of the isolated pure components: if one component is a liquid at room temperature, the crystals are designated as solvates; if both components are solids at room temperature, the crystals are designated as co-crystals. The different structural arrangements of the APIs lead to by changes in the physical and chemical properties (e.g. thermodynamic, spectroscopic, kinetic, interfacial, mechanical, etc.), which may induce differences in manufacturability, solubility, bioavailability and stability between the different solid forms. Understanding and controlling the solid-state chemistry of APIs, both as pure drug substances and in formulated products, is therefore an important aspect of the drug development and formulation processes and has a direct impact on the quality as well as the protection of the intellectual property against possible patent related infringements. In order to obtain an accurate description of the solid forms of an API, analytical techniques sensitive to the crystalline structure must be applied. In principle, single crystal X-ray diffraction is the most effective technique since it directly determines the packing, conformation and intermolecular interaction of molecules. However, due to the problems associated with obtaining good quality single crystals, and the need of reliable routine analytical methods (sometimes suitable as on-line monitoring tools), the use of vibrational spectroscopy in this field is gaining increasing attention. Differently to X-ray diffraction techniques, which are sensitive to the long-range order, vibrational spectroscopy (mid-infrared, near-infrared and Raman scattering) is primarily sensitive to the short-range structure of molecular solids. Both Raman and infrared spectroscopies provide information on the structure, configuration and conformation in the solid state by probing the vibrations of atoms. Qualitative as well as quantitative analysis can be performed with both techniques. In this presentation, we will review the main applications of the vibrational spectroscopy techniques in the characterization of the solid forms of pharmaceutical substances. Specific examples of qualitative and quantitative investigations of raw materials and formulated products will be discussed and correlated with the results of other experimental techniques and quantum mechanical calculations. (author)

[en] Full text: The research about renewable energy sources has attracted attention since there is a high demand for clean energy around the world. In the case of solar energy, a prominent field is the investigation of multiferroic materials for applications in photovoltaic cells. In this scenario, KBiFe₂O₅ (KBFO) emerged as a strong candidate for such applications given mostly by its low bandgap energy. At room temperature, KBFO crystallizes in an orthorhombic structure and possesses interesting electronic properties making it suitable also for photovoltaic applications. Besides, it is reported that such structure transforms into a monoclinic one in very high temperatures and pressures. In this work, we obtained the monoclinic structure of KBFO at room temperatures and performed an analysis of the structural and vibrational properties of KBFO using Raman spectroscopy and Synchrotron X-ray powder diffraction (SXRPD) techniques under hydrostatic pressure variation. The study of Raman spectra obtained at high pressures revealed a first order phase transition in the material, characterized by a pressure hysteresis. Synchrotron X-ray powder diffraction (SXRPD) under varying pressure was employed to confirm such structural pressure-induced phase transition. An integrated evaluation of the results obtained by Raman and SXRPD techniques indicates that, possibly, the symmetry for the high-pressure crystalline phase belongs to the space group Pmmm. (author)

No abstract available

[en] Dielectric constant and ac and dc electrical conductivity measurements have been performed in single crystals of the fluorite compound KY₃F₁₀, in the temperature range 100 to 770 K. The dielectric response shows both dipolar and charge carrier contributions. The electrical conductivity varied more than 11 orders of magnitude and showed the existence of two thermally activated processes, with activation energies of 1.71(1) eV and 1.17(1) eV, for the higher and lower temperature regions, respectively. The conduction mechanisms have been discussed in terms of the different conduction pathways for the fluorine vacancy motion in the crystal. (author)

[en] Complete text of publication follows. A systematic quantum mechanical study of the possible conformations, their relative stabilities and vibrational spectra of efavirenz has been reported. Efavirenz, (S)-6-chloro-4(cyclopropylethynyl)- 1, 4-dihydro-4-(trifluoromethyl)-2H-3,1-benzoxazin-2-one, is a novel anti HIV agent belonging to the class of the non-nucleoside inhibitors of the HIV-1 virus reverse transcriptase [1]. Structural and spectral characteristics of efavirenz have been studied by methods of infrared, Raman spectroscopy and quantum chemistry. Density functional theory (DFT) calculations for potential energy curves, optimized geometries and vibrational spectra have been carried out using 6-311++G(d, p) basis sets and B3LYP functionals. Based on these results, we have discussed the correlation between the vibrational modes and the crystalline structure of the most stable form of efavirenz. A complete analysis of the experimental infrared and Raman spectra has been reported on the basis of frequency of the vibrational bands and potential energy distribution over the internal coordinates and characteristic bands have been identified. Plots of infrared and Raman spectra of the molecule based on DFT calculations show reasonable agreement with the experimental spectra.