Studies of new antiferroelectric liquid crystal based on quantum-chemical model

Physical properties of new thermotropic antiferroelectric liquid crystal have been studied. Experiments were done by use of complementary methods such as differential scanning calorimetry, polarizing optical microscopy and X-ray powder diffractometry. Acquired data from X-ray powder diffractometry was examined under application of quantum chemical approach. It has been found that compound studied exhibits stable enantiotropic antiferroelectric SmC_{A}^{*} phase in the wide temperature range while ferroelectric phase SmC^{*} is very narrow

Magnetite thin films

A low temperature process for converting hematite (α-Fe_2O_3) thin films into magnetite (Fe_3O_4) is described. The films produced are unambiguously identified as magnetite by several complementary methods of analysis. These include α-backscattering spectrography, X-ray powder diffractometry, and observations of electrical, magnetic, and optical properties

Melem (2,5,8-Triamino-tri-s-triazine), an Important Intermediate during Condensation of Melamine Rings to Graphitic Carbon Nitride: Synthesis, Structure Determination by X-ray Powder Diffractometry, Solid-State NMR, and Theoretical Studies

Single-phase melem (2,5,8-triamino-tri-s-triazine) C6N7(NH2)3 was obtained as a crystalline powder by thermal treatment of different less condensed C−N−H compounds (e.g., melamine C3N3(NH2)3, dicyandiamide H4C2N4, ammonium dicyanamide NH4[N(CN)2], or cyanamide H2CN2, respectively) at temperatures up to 450°C in sealed glass ampules. The crystal structure was determined ab initio by X-ray powder diffractometry (Cu Kα1:  P21/c (No. 14), a = 739.92(1) pm, b = 865.28(3) pm, c = 1338.16(4) pm, β = 99.912(2)°, and Z = 4). In the solid, melem consists of nearly planar C6N7(NH2)3 molecules which are arranged into parallel layers with an interplanar distance of 327 pm. Detailed 13C and 15N MAS NMR investigations were performed. The presence of the triamino form instead of other possible tautomers was confirmed by a CPPI (cross-polarization combined with polarization inversion) experiment. Furthermore, the compound was characterized using mass spectrometry, vibrational (IR, Raman), and photoluminescence spectroscopy. The structural and vibrational properties of molecular melem were theoretically studied on both the B3LYP and the MP2 level. A structural optimization in the extended state was performed employing density functional methods utilizing LDA and GGA. A good agreement was found between the observed and calculated structural parameters and also for the vibrational frequencies of melem. According to temperature-dependent X-ray powder diffractometry investigations above 560°C, melem transforms into a graphite-like C−N material

Influence of particle size and structure of ZrO2 on microstructure development and dielectric constant of PbZr0.5Ti0.5O3

The synthesis of PbZr0.5Ti0.5O3 ceramics from the raw materials was reinvestigated in order to find relations in the characterizations for the products in various stages of the preparation procedure. Techniques used were particle size measurements, X-ray powder diffractometry, density and dielectric constant measurements and scanning electron microscopy. The results show, that the particle size and structure of ZrO2 determine the inhomogeneity, expressed as xt/xr, of the calcination product. An inhomogeneous calcination product sintered at relatively low temperatures results in an inhomogeneous ceramic of low density. Using high sintering temperatures and long periods of time an inhomogeneous calcination product converts into a dense (>97%) and homogeneous ceramic

Characterization of biominerals in species of <i>Canna</i> (Cannaceae)

Plant biominerals are not always well characterized, although this information is important for plant physiology and can be useful for taxonomic purposes. In this work, fresh plant material of seven wild neotropical species of genus Canna, C. ascendens, C. coccinea, C. indica, C. glauca, C. plurituberosa, C. variegatifolia and C. fuchsina sp. ined., taken from different habitats, were studied to characterize the biominerals in their internal tissues. For the first time, samples from primary and secondary veins of leaves were investigated by means of infrared spectroscopy, complemented with X-ray powder diffractometry and scanning electron microscopy. The spectroscopic results, supported by X-ray powder diffractometry, suggest that the calcium oxalate is present in the form of whewellite (CaC2O4×H2O) in all the investigated samples. It is interesting to emphasize that all IR spectra obtained were strongly similar in all species studied, thus indicating an identical chemical composition in terms of the biominerals found. In this sense, the results suggest that the species of Canna show similar ability to produce biogenic silica and produce an identical type of calcium oxalate within their tissues. These results can be an additional trait to support the relationship among the families of Zingiberales.Facultad de Ciencias Naturales y Muse

Transformation of Ammonium Dicyanamide into Dicyandiamide in the Solid

Ammonium dicyanamide NH4[N(CN)2] was synthesized through aqueous ion exchange. The crystal structure was investigated by single-crystal X-ray diffraction (P21/c, a = 378.67(6) pm, b = 1240.9(3) pm, c = 911.84(14) pm, β = 91.488(18)°, Z = 4). It derives from the CsCl structure type. Medium strong hydrogen bonds between NH4+ and [N(CN)2]- ions are indicative of the observed formation of dicyandiamide H4C2N4 during heating. According to DSC and temperature-dependent X-ray powder diffractometry, this isomerization is exothermic and occurs between 102 and 106°C in the solid. The reaction represents the isolobal analogue to the classical synthesis of urea by heating NH4OCN. While other alkali and alkaline earth dicyanamides undergo trimerization or polymerization of their anions during heating, ammonium dicyanamide thus shows a different reactivity

Synthesis, characterization and thermal behaviour of solid 2-methoxycinnamylidenepyruvate of light trivalent lanthanides

Solid state Ln-2-MeO-CP compounds, where Ln stands for light trivalent lanthanides (La, Ce, Pr, Nd, Sm, Eu, Gd) and 2-MeO-CP is 2-methoxycinnamylidenepyruvate, were synthesized in this work. Simultaneous thermogravimetry and differential thermal analysis (TG-DTA), differential scanning calorimetry (DSC), X-ray powder diffractometry, experimental and theoretical infrared spectroscopy and complexometry were used to characterize and to study the thermal behaviour of these compounds. The results led to information regarding the composition and stability of the isolated complexes

Determination of Mica Cell Parameters by X-Ray Powder Diffractometry — A Case Study

Possibilities and restrictions of least-square methods for mica cell refinement are briefly described. If diffractometric raw data are precise and accurate, and if geometrical errors are properly corrected, a cell refinement (determination of ao, bo, cO, β) can be carried out rapidly, but the reliability of obtained data has to be evaluated carefull

Order-Disorder Transition in Urea-Polyethylene Complex

The phase transition of urea complexes whose guest components range from n-paraffin to polyethylene was investigated by DSC thermal analysis. The transition temperatures increased with increasing the chain length; the related heats did not change much with the chain length. An X-ray powder diffractometry for urea-polyethylene complex revealed that the complex undergoes the same kind of phase transition between orthorhombic and hexagonal as urea-n-paraffin complex. The transition is interpreted in terms of an order-disorder transition with respect to the orientation of the guest molecule