Double perovskite crystals of nominal composition PbMn1/2Nb1/2O3 were grown by spontaneous crystallization. Their structure has been studied by X-ray diffraction on a powder prepared by grinding crystals. According to the results of the Rietveld structure analysis, the powder includes phases of perovskite Ph1 ( 75.5 wt Pm3̅m (221)) with compositions Pb1.000(4)Mn0.54(2)Nb0.46(2)O3 and Pb1.00(1)Mn0.32(5)Nb0.68(5)O3, respectively, and the impurity phase of PbO ( 3.2 wt
An X-ray structural analysis of tsepinite-K from the pegmatite no. 62, Karnasurt Mountain, Lovozero alkaline massif (Kola Peninsula), was performed. The mineral belongs to the labuntsovite group and differs from other its representatives in a “combined” structural type (partial occupancy of the key D position). Its structure was previously studied within the space group Cm. A repeated study of the structural features of tsepinite-K was carried out with the transition to space group Pm. The unit-cell parameters are a = 14.3265(3) Å, b = 13.802(2) Å, c = 7.783(1) Å, β = 116.949(3)°, V = 1371.8 Å3; R = 0.042 for 1677 reflections with F > 2σ(F). A more detailed ordering of cations over structure positions was established.
A kinematical theory of a restricted X-ray beam diffraction in a bent crystal has been developed, enabling calculations of reciprocal space maps. A solution is obtained in the form of a Fourier integral equation, where the integrand is written in terms of Fresnel integrals. Numerical simulation of the angular distribution of diffracted intensity in reciprocal space from a plane-parallel plate, as well as from slightly and strongly curved crystals, is performed based on the obtained solution and two-dimensional recurrence relations. The results of calculations performed by the two methods are compared.
This study utilized corn stover as the biomass feedstock to produce stover charcoal (CC) through modification with oxalic acid. The charcoal was then composited with polyvinylidene fluoride (PVDF) using a coating-crosslinking method, resulting in CC/PVDF composite membranes. By optimizing key parameters including crosslinking agent concentration, crosslinking time, and charcoal loading, a composite membrane with outstanding ammonia adsorption performance was obtained. The membrane’s morphology, chemical composition, and mechanical properties were characterized by scanning electron microscopy, infrared spectroscopy, and a universal testing machine. The results indicate that the optimal ammonia adsorption capacity of 40.4 mg/cm2 was achieved under the following conditions: a binder ratio of 1 : 2, a crosslinking agent concentration of 3
Applying the technique of gradient melt freezing in a fluorinating atmosphere, large single-phase blocks of cerium fluoride crystals with a characteristic brown color, associated with quenching of point defects, were fabricated, and the influence of the formed color centers on the optical transmission and ionic conductivity of CeF3 during thermal heating in a vacuum was studied. The material under study crystallizes in the sp. gr. P3̅c1 and is characterized by additional optical absorption in the wavelength range of 350−650 nm, caused by the formation of color centers. Annealing of CeF3 at temperatures up to 827 K leads to thermal destruction of defect centers and release of fluorine vacancies, which causes an increase in the ionic conductivity of the crystals by ∼2 times as compared to the initial level, reaching a value of σdc = 3.5 × 10−4 S/cm (500 K), while maintaining the ion-transfer activation enthalpy ΔHa = 0.37 eV. The obtained results can be used to develop modes of post-growth thermal annealing of Се3+-based crystalline materials.
