I. Jendrzejewska

Effect of Cation Substitution on Critical Fields in the n-type Zn_{x}Sn_{y}Cr_{z}Se_{4} Spinel Semiconductors

The ac dynamic magnetic susceptibility was used to study a cation substitution on critical fields in polycrystalline (Zn0.87Sn0.048)Cr2.02Se4 and Zn0.93[Cr1.95Sn0.05]Se4 spinels with tetraand octahedral coordination of Sn ions, respectively. An increasing static magnetic field shifts the Néel temperature TN to lower temperatures while a susceptibility peak at Tm in the paramagnetic region — to higher temperatures. Below TN the magnetic field dependence of susceptibility, χac(H), shows two peaks at critical fields Hc1 and Hc2. The values of Hc1 decrease slightly with temperature while the values of Hc2 decrease strongly with temperature, especially for spinel with octahedral coordination of Sn ions, suggesting a weakness of the ferromagnetic component.

Application of X-ray powder diffraction and differential scanning calorimetry for identification of counterfeit drugs

X-ray analysis confirmed that in all investigated samples, the active API (acetylsalicylic acid and ascorbic acid) was present. The values of the interplanar distance dhkl for the studied samples are in good accordance with those presented in the ICDD database. The intensities of the diffraction lines depend on the content of the component in the tested preparation. Therefore, different intensities of lines for the APIs were observed in the obtained diffraction patterns. Thermal analysis of the studied substances showed that during the thermal analysis, the following phenomena might occur: dehydration and (or) melting, crystalline transformation. Moreover, it was found that the chemical structure of the studied compounds affects the process of their thermal decomposition. The data obtained during these investigations can be useful in quick tests of physicochemical discrepancies and abnormalities between potential components of pharmaceutical preparations. The evidence for the interaction can be obtained by comparing DSC and TG curves of the drug and the excipient, as well as those of their physical mixtures. For this reason, the study of characteristics of thermal decomposition of drugs and excipients is necessary. Based on the above investigations, it may be stated that a combination of two methods: XRPD and DSC can be used to distinguish the original drugs from counterfeit products, e.g., by checking for the presence of the correct API or by a comparison of the drugs fingerprint.Graphical Abstract

X-Ray Investigations of Polycrystalline Compounds with General Formula ZnCr2-xNdxSe4

Abstract. The polycrystalline compounds in the ZnCr2-xNdxSe4 system were prepared by the ceramic method in closed silica tubes using ZnSe, Nd2Se3, and Cr2Se3 as starting materials. The chemical composition and structural data has been determined by X-ray diffraction. The observed symmetry is cubic, space group . For ZnCr1.95Nd0.05Se4 compounds, a pure spinel phase forms for stoichiometric and smaller amounts of ZnSe. For both compounds of ZnCr1.90Nd0.10Se4, near spinel phase, a foreign ZnSe phase exists. It may indicate that 10% doping is close to the solubility limit of Nd in ZnCr2Se4.