Progress in Solid State Chemistry最新文献

Single phasic nanostructured YMnO₃ manganites were successfully synthesized by employing acetate precursor based modified sol–gel technique followed by their sintering at different temperatures. Structural studies were carried out by performing X–ray diffraction (XRD) measurement and Rietveld analysis on raw data of XRD. Particle size and shape were studied using transmission electron microscopy (TEM) while size distribution was investigated by performing particle size analyzer. Nanostructured samples were studied for their electrical properties under low applied magnetic field of 1.2T. Frequency and magnetic field dependent dielectric behavior has been understood on the basis of boundaries between the particles and inverse Dzyaloshinskii–Moriya (DM) interaction. Nanostructured YMnO₃ manganites exhibit positive magnetodielectric (MD) effect. Universal dielectric response (UDR) model and relaxation mechanism have been employed for dielectric behavior of the samples understudy. Role of particle morphology and magnetic disorder have been discussed for the understanding of impedance and negative magnetoimpedance (MI) of the samples. Frequency and magnetic field dependent variation in conductivity has been explained using boundary and magnetic disorders and free charge carriers in the samples. All nanostructured YMnO₃ show positive Magnetoconductivity (MC) throughout the frequency and magnetic field range studied. Variation in voltage dependent hysteretic capacitance and estimated built–in potential have been discussed in the context of the role of defects, vacancies, disorder and free charge carriers in the samples sintered at different temperatures.

Evolved gas analysis (EGA) mass-spectrometry (MS) is used to characterize the solid state pyrolysis decomposition pathways of air- and moisture-sensitive organometallic compounds. In this study, the single-source GaAs compounds (Et₂AsGaEt₂)₃ (1), (t-Bu₂AsGaEt₂)₂ (2), and [t-Bu(H)AsGaEt₂]₂ (3) were heated in capillary tubes under inert condition and the volatile products were analyzed by MS. In addition, the relative ratios of evolved gases were characterized using gas chromatography (GC), while the solid state pyrolysis products were analyzed by EDS, ¹H NMR and XRD. Pyrolysis of GaAs single-source materials in the solid state reveals chemical information on the stability of the GaAs bond, an observation masked in gas-phase analysis of single-source materials during chemical vapor deposition. Information on GaAs bond stability may be elucidated due to the volatility of the by-products formed during Ga-As precursor pyrolysis. Loss of GaAs bond integrity in materials with alkyl substitution on Ga and As leads to formation of mobile and volatile alkyl diarsine species, as was observed for the pyrolysis of 1. An in-situ method to monitor solid-state pyrolysis by mass spectrometry identified the loss of a tetraalkyl-diarsine as the critical factor that drives formation of sub-stoichiometric GaAs products from single-source precursors. Replacing a single alkyl group on the As atom with a H (precursor 3) leads to the loss of an alkane instead of tetraalkyl-diarsine formation. Solid-state pyrolysis precursor 3 results in the formation of polycrystalline GaAs in up to 58% yield with a 52:48 Ga:As stoichiometry.

Structure and its transformation are examined for amorphous Se-rich As_xSe_1-x (0 ≤ x ≤ 0.2) alloys by employment of diffraction and non-diffraction structural probes. It is shown that the molecular structure of amorphous Se (a-Se) on the scale of short-range order is close to that of crystalline phase, while medium-range order differs from the structure of most inorganic glasses and may be placed between three-dimensional network glasses and polymeric ones. Further experiments show the existence of successive phases in laser-induced glass-crystalline transition with pronounced threshold behavior. Below the energy density threshold, E_th, only small changes in the local structure of the system can be detected. Above E_th, the changes were attributed to crystallization transformation. The corresponding Raman spectra reveal transformation of the system from amorphous into the crystalline phase under laser irradiation. In the binary As_xSe_1-x glass system, a change of structural regime takes place near the composition x ≈ 0.04. The presence of this topological threshold is established by direct and indirect evidence, such as peculiarities in the composition dependence of the basic parameters for electron diffraction and Raman vibration modes. The peculiarities are caused by the transition from a chain-ring-like structure to preferentially a chain-like structure. Experiments described in this section have shown that Raman technique is a particularly sensitive method to determine the presence of microcrystal's in the glassy matrix. Room-temperature polarized Raman scattering spectra of model glass have been collected. Low-frequency peaks were observed in the spectra. A model is proposed for explanation of their appearance. It is shown clearly that the low-frequency Raman spectra allow determining the conditions at the boundaries, sizes as well as concentration of micro-heterogeneities in non-crystalline materials. It was established earlier that for all amorphous (glassy) materials a low-frequency peak, observed in the corresponding spectral region of Raman scattering and called boson peak, is inherent. This peak is absent in crystals of the same chemical composition and is associated with space correlations on the scale of medium-range order R_c ≈ 10 Å. On the contrary, less known is that a boson peak can give important information about the presence of microcrystalline inclusions and heterogeneities in the low-frequency Raman spectra of glasses irrespective to their chemical composition.

Carboxylated fullerenes may have wide applications in science and technology. Therefore, there is particular interest in investigating the physico-chemical and biological properties and the applications of these compounds. This review systematizes the current literature data on the synthesis, physico-chemical properties and application of carboxylated fullerenes as nanomodifiers of polyelectrolytes as well as their use in medicine and agriculture. Presented experimental and theoretical data gives a comprehensive overview of these substances and can be valuable to specialists in the fields of nanotechnology, nanomaterials and bionanomedicine.

The paper reports a thorough investigation of little inspected two classes of group VIIA based crystals: interhalogen compounds ClF, ClF₃, BrF₃ and IF₃ on one hand and halogen suboxides F₂O, Cl₂O and Br₂O on the other hand, as well as rare gas fluorides (here exemplarily XeF₄), all exhibiting peculiar stereochemistry of electron (non-bonding) lone pairs merging in forms of twins and triplets. Particularly with respect to the well known VSEPR (Valence Shell Electron Pair Repulsion) model we present original approach merging crystal chemistry and density functional theory (DFT) electron localization function (ELF) to provide accurate topologic analyses and precise metrics of electron lone pairs geometries. In this context we rewrite the chemical formulae above by adjoining E designing the lone pair (LP) and M* formulating the LP-bearing element: ClF{E₃}, M*₂OE₂{E₃}₂ (M* = F, Cl, Br), M*F₃E₂ (M* = Cl, Br, I) and XeF₄E₂. Then in ClF{E₃} and M*₂OE₂{E₃}₂ (M* = F, Cl, Br) family an original stereochemistry is developed with LP concentration in E triplets which generate electronic torus revolving around Cl and M* which in the neighborhood of largely electronegative F, exhibit cationic-like behavior. E around Cl in ClF and then around M* of the series under consideration exhibits an ellipsoidic shape with an equivalent sphere of influence radius (r_E) increasing along with the atomic number Z, i.e. r_{E_F} = 0.52 Å, r_{E_Cl} = 0.65 Å and r_{E_Br} = 0.70 Å. From selected sections in ELF data we obtained precise topology and metrics details of these tori. For M*₂OE₂{E₃}₂ family the E twins attached to O have also been localized, their size remaining constant with r_{E_O} = 0.68 Å in all studied compounds. The lone pair twins in the series M*F₃E₂ (M* = Cl, Br, I; M* trivalent oxidation state) as well as in noble gas tetrafluoride XeF₄E₂ provide remarkable examples: rE evolution versus Z, r_{E_Cl} = 0.77 Å (Z = 17), r_{E_Br} = 0.85 Å (Z = Br) and r_{E_I} = 0.90 Å (Z = 53), follow a linear expansion while in the xenon case with a close Z_Xe = 54 but with tetravalent oxidation state, Xe exhibits a radius r_{E_Xe} = 0.95 Å, indicating the important influence of the charge magnitude on E volume. The interaction of cations with E centroïd: Ec -defined as the electronic volume attached to the lone pair- of neighboring molecules is plausible in explaining unusually short distances between cations. Even surrounded by E torus the cations obviously exert attractive influence through