Thermochemical studies on SrFe12O19(s)

The citrate-nitrate gel combustion route was used to prepare SrFe₁₂O₁₉(s) powder sample and the compound was characterized by X-ray diffraction analysis. A solid-state electrochemical cell of the type: (−)Pt, O₂(g)/{CaO(s) + CaF₂(s)}//CaF₂(s)//{SrFe₁₂O₁₉(s) + SrF₂(s) + Fe₂O₃(s)}/O₂(g), Pt(+) was used for the measurement of emf as a function of temperature from 984 to 1151 K. The standard molar Gibbs energy of formation of SrFe₁₂O₁₉(s) was calculated as a function of temperature from the emf data and is given by: (SrFe₁₂O₁₉, s, T)/kJ mol⁻¹ (±1.3) = −5453.5 + 1.5267 × (T/K). Standard molar heat capacity of SrFe₁₂O₁₉(s) was determined in two different temperature ranges 130-325 K and 310-820 K using a heat flux type differential scanning calorimeter (DSC). A heat capacity anomaly was observed at 732 K, which has been attributed to the magnetic order-disorder transition from ferrimagnetic state to paramagnetic state. The standard molar enthalpy of formation, (298.15 K) and the standard molar entropy, (298.15 K) of SrFe₁₂O₁₉(s) were calculated by second law method and the values are −5545.2 kJ mol⁻¹ and 633.1 J K⁻¹ mol⁻¹, respectively.     

Structural and optical properties of polycrystalline CdSexTe1−x (0 ≤ x ≤ 0.4) thin films

CdSe_xTe_1−x (0 ≤ x ≤ 0.4) ternary thin films have been deposited on quartz substrates at room temperature by a single source thermal evaporation. X-ray diffraction patterns and transmission electron microscope micrographs of these films showed that the films were of polycrystalline texture over the whole range studied and exhibit predominant cubic (zinc blende) structure with strong preferential orientation of the crystallites along (1 1 1) direction. Linear variation of the lattice constant with mole fraction x is observed obeying Vegard's law. The dependence of the optical constants, the refractive index n and extinction coefficient k, of the films on the mole fraction x was studied in the spectral range of 400-2500 nm. The normal dispersion of the refractive index of the films could be described using the Wemple-DiDomenco single-oscillator model. CdSe_xTe_1−x thin films of different composition have two direct and indirect transitions corresponding to energy gaps and . The variation in either or with x indicates that this system belongs to the amalgamation type. The variation follows a subquadratic dependence and the bowing parameters were found to be 0.36 and 0.48 eV for the direct, and indirect energy gaps, respectively. Direct linear variation of the ratio N/m^* with x is observed.     

Synthesis and characterization of a new organic dihydrogenomonophosphate [3,5-(CH3O)2C6H3NH3]2(H2PO4)2

Chemical preparation, crystal structure, calorimetric studies and spectroscopic investigation are given for a new organic cation dihydrogenomonophosphate [3,5-(CH₃O)₂C₆H₃NH₃]₂(H₂PO₄)₂. This compound is triclinic with the following unit cell parameters: a=9.030(6) Å, b=16.124(5) Å, c=8.868(3) Å, α=75.04(3)°, β=110.71(4)°, γ=104.61(1)°, Z=4, V=1148.0(1) Å³, Z=2 and ρ_cal.=1.454 g cm⁻³. Crystal structure was solved and refined to R=0.04, 2752 independent reflections. The atomic arrangement can be described as inorganic layers of H₂PO₄⁻ anions parallel to planes, between which are located the organic groups. Solid-state and MAS-NMR spectroscopies are in agreement with the X-ray structure. Ab initio calculations allow the attribution of the phosphorous and carbon signals to the independent crystallographic sites and to the various atoms of the organic groups.     

Contact angle of water droplet on apatite single crystals

Contact angles of water droplets on well-formed crystals of strontium and barium chlorapatites, Sr₅Cl(PO₄)₃ and Ba₅Cl(PO₄)₃, were observed. The contact angles of water on (1 0  0) and (1 0  1) faces of Sr₅Cl(PO₄)₃ were 74±8° and 53±5° and those on (1 0  0) and (1 0  1) faces of Ba₅Cl(PO₄)₃ were 52±5° and 33±1°, respectively. The surface tensions of the crystals were calculated using Neumann’s equation. They were 39.2±50 and 52.0±3.0 mJ m⁻² for (1 0  0) and (1 0  1) faces of Sr₅Cl(PO₄)₃, 52.5±2.9 and 63.0±0.5 mJ m⁻² for (1 0  0) and (1 0  1) faces of Ba₅Cl(PO₄)₃, respectively. The (1 0  1) face has larger surface tension than (1 0  0) face for both crystals. The chlorapatite crystals have tendency to elongate in 〈0 0 0 1〉 directions during the crystal growth process, indicating that (1 0  0) face is more stable than (1 0  1) face. This nature of crystal morphology is consistent with the surface tensions estimated from the water contact angles. The higher density of Ba₅Cl(PO₄)₃ than Sr₅Cl(PO₄)₃ is considered to cause the smaller contact angles of water droplet on Ba₅Cl(PO₄)₃ crystal than that on Sr₅Cl(PO₄)₃ crystal because the attractive force between the heavier atoms brings the larger surface tension of solid.     

A novel nanostructured composite formed by interaction of copper octa(3-aminopropyl)octasilsesquioxane with azide ligands: Preparation, characterization and a voltammetric application

This study presents the preparation, characterization and application of copper octa(3-aminopropyl)octasilsesquioxane following its subsequent reaction with azide ions (ASCA). The precursor (AC) and the novel compound (ASCA) were characterized by Fourier transform infrared spectra (FTIR), nuclear magnetic resonance (NMR), electron paramagnetic resonance (EPR), scanning electronic microscopy (SEM), X-ray diffraction (XRD), Thermogravimetric analyses and voltammetric technique. The cyclic voltammogram of the modified graphite paste electrode with ASCA (GPE-ASCA), showed one redox couple with formal potential () = 0.30 V and an irreversible process at 1.1 V (vs. Ag/AgCl; NaCl 1.0 M; v=20 mV s−1). The material is very sensitive to nitrite concentrations. The modified graphite paste electrode (GPE-ASCA) gives a linear range from 1.0 × 10⁻⁴ to 4.0 × 10⁻³ mol L⁻¹ for the determination of nitrite, with a detection limit of 2.1 × 10⁻⁴ mol L⁻¹ and the amperometric sensitivity of 8.04 mA/mol L⁻¹.