Polymorphism of the Co-Te nanophases in mechanochemical synthesis.

The mechanochemical synthesis of all cobalt tellurides' phases is demonstrated in this work. The samples had their structural, microstructural, and magnetic characterizations performed by X-ray powder diffraction, transmission electron microscopy, and magnetometry techniques. The initial atomic stoichiometries tested of Co32Te68 and Co40Te60 resulted in the synthesis of the γ-CoTe2 Pnnm (marcasite), α-CoTe2 Pa3̄ (pyrite), α-CoTe2 P3̄m1 (CdI2-like), and ß-CoTe P63/mmc phases with different weight proportions in the sample. Modeling of the X-ray diffractograms employed conventional double-Voigt and crystallite shape-anisotropy DV approaches to show that the volumetric diameter average and true crystallite size of the diffraction domains are in the range of tens of nanometers. Transmission electron microscopy measurements also allowed distribution counting of the crystallite sizes via maximum caliper diameter. Electron diffraction experiments presented comparable structural parameters with Rietveld via the analysis of the Debye rings. A model using the Langevin approaches showed the phases to present both ferromagnetic and superparamagnetic contributions attributed to weakly-interacting metallic Co grains with magnetic domain sizes ranging between 2.3 and 4.0 nm. The phases' evolution with storage time was analyzed over two years and revealed to be stable regarding their structural and microstructural properties.

Structural, microstructural and magnetic characterization of the ß-CoTe nanophase synthesized by a novel mechanochemical method.

This work reports an unprecedented mechanochemistry synthesis of ß-CoTe and its systematic characterization through X-ray powder diffraction (XRPD), transmission electron microscopy (TEM), and magnetometry techniques. The mechanical alloying produced the desired material within 6 h along with minor impurities, showing good stabilization for higher milling times (15 h) and long-term storage. XRPD characterization employed the Rietveld profile fitting analysis with fundamental parameters analysis in a direct convolution approach, giving the material's structure and microstructure information. For the spherical shape, the diameter mass average of the crystallites furnished values around 13 nm with 1.1% of microstrain. The double-Voigt procedure also modeled a triaxial ellipsoid shape for the crystallite size and obtained a surface-weighted average value for its volume around 150 nm3. TEM images confirmed the nanometric size visually and showed the crystallites to aggregate in large particles hundreds of nanometers in size. Measuring hundreds of supposed crystallite sizes, we could achieve a numerical distribution of their sizes with an average of 16 nm. The magnetization analysis performed both experimentally and via numerical simulations showed that ß-CoTe is predominantly superparamagnetic with a magnetic domain size compatible with the double-Voigt one.

Irbesartan desmotropes: Solid-state characterization, thermodynamic study and dissolution properties.

Irbesartan (IBS) is a tetrazole derivative and antihypertensive drug that has two interconvertible structures, 1H- and 2H-tautomers. The difference between them lies in the protonation of the tetrazole ring. In the solid-state, both tautomers can be isolated as crystal forms A (1H-tautomer) and B (2H-tautomer). Studies have reported that IBS is a polymorphic system and its forms A and B are related monotropically. These reports indicate form B as the most stable and less soluble form. Therefore, the goal of this contribution is to demonstrate through a complete solid-state characterization, thermodynamic study and dissolution properties that the IBS forms are desmotropes that are not related monotropically. However, the intention is also to call attention to the importance of conducting strict chemical and in solid-state quality controls on the IBS raw materials. Hence, powder X-ray diffraction (PXRD) and Raman spectroscopy (RS) at ambient and non-ambient conditions, differential scanning calorimetry (DSC), hot stage microscopy (HSM), Fourier transform infrared (FT-IR) and scanning electron microscopy (SEM) techniques were applied. Furthermore, intrinsic dissolution rate (IDR) and structural stability studies at 98% relative humidity (RH), 25 °C and 40 °C were conducted as well. The results show that in fact, form A is approximately four-fold more soluble than form B. In addition, both IBS forms are stable at ambient conditions. Nevertheless, structural and/or chemical instability was observed in form B at 40 °C and 98% RH. IBS has been confirmed as a desmotropic system rather than a polymorphic one. Consequently, forms A and B are not related monotropically.