Infrared and Raman spectra and normal coordinate calculations on trirutile-type compounds

Crystal Chemistry, Raman Spectra, and Bond Characteristics of Trirutile-Type Co0.5Ti0.5TaO4 Microwave Dielectric Ceramics

A novel trirutile-type Co_0.5Ti_0.5TaO₄ ceramic was reported here for the first time. The correlations between the sintering behavior, crystal structure, chemical bond, and dielectric properties were investigated. Pure Co_0.5Ti_0.5TaO₄ ceramic was synthesized in the temperature range of 1000-1100 °C. A trirutile structure and refined parameters of a = b = 4.71163 Å, c = 9.13586 Å, and V_cell = 202.811 ų could be obtained (1075 °C). According to the P-V-L chemical bond theory, majority contributions to the dielectric constant originated from Ta-O bonds, owing to its largest bond ionicity and bond susceptibility values. The experimental dielectric constant is close to the theoretical values calculated via the P-V-L chemical bond theory and Clausius-Mossotti relationship. The Ta-O bonds that present the largest lattice energy are also the main factors influencing the intrinsic loss. The τ_f value is consistent with the oxygen distortions of the octahedron. More importantly, variations of the densification, average grain size, and grain boundary are crucial factors for development of the microwave dielectric properties. The Raman spectra and group theory were analyzed together, and the results indicated that the A_1g mode at 687.45 cm^-1, which reflects the stretching vibrations of the O anions, dominates the Raman vibrations. Typical microwave dielectric properties of Co_0.5Ti_0.5TaO₄ ceramics were obtained when sintered at 1075 °C: ε_r = 40.69, Qf = 17291 GHz, and τ_f = 114.54 ppm/°C.

Sensitivity Tests of Pellets Made from Manganese Antimonate Nanoparticles in Carbon Monoxide and Propane Atmospheres

Nanoparticles of manganese antimonate (MnSb₂O₆) were prepared using the microwave-assisted colloidal method for its potential application as a gas sensor. For the synthesis of the oxide, manganese nitrate, antimony chloride, ethylenediamine and ethyl alcohol (as a solvent) were used. The precursor material was calcined at 800 °C in air and analyzed by X-ray diffraction. The oxide crystallized into a hexagonal structure with spatial group P321 and cell parameters a = b = 8.8054 Å and c = 4.7229 Å. The microstructure of the material was analyzed by scanning electron microscopy (SEM), finding the growth of microrods with a size of around ~10.27 μm and some other particles with an average size of ~1.3 μm. Photoacoustic spectroscopy (PAS) studies showed that the optical energy band (Eg) of the oxide was of ~1.79 eV. Transmission electron microscopy (TEM) analyses indicated that the size of the nanoparticles was of ~29.5 nm on average. The surface area of the powders was estimated at 14.6 m²/g by the Brunauer⁻Emmett⁻Teller (BET) method. Pellets prepared from the nanoparticles were tested in carbon monoxide (CO) and propane (C₃H₈) atmospheres at different concentrations (0⁻500 ppm) and operating temperatures (100, 200 and 300 °C). The pellets were very sensitive to changes in gas concentration and temperature: the response of the material rose as the concentration and temperature increased. The results showed that the MnSb₂O₆ nanoparticles can be a good candidate to be used as a novel gas sensor.

Nanostructuring of a one-dimensional zinc antimonate electrode material through a precipitation strategy for use in supercapacitors

The electrochemical properties of ZnSb₂O₆ nanorods consisting of two types of heterovalent metal cations, Zn²⁺ and Sb⁵⁺, have been investigated.

Structural and Magnetic Properties of the Trirutile-type 1D-Heisenberg Anti-Ferromagnet CuTa2O6

We prepared trirutile-type polycrystalline samples of CuTa₂O₆ by low-temperature decomposition of a Cu-Ta-oxalate precursor. Diffraction studies at room temperature identified a slight monoclinic distortion of the hitherto surmised tetragonal trirutile crystal structure. Detailed high-temperature X-ray and neutron powder diffraction investigations as well as Raman scattering spectroscopy revealed a structural phase transition at 503(3) K from the monoclinic structure to the tetragonal trirutile structure. GGA+U density functional calculations of the spin-exchange parameters as well as magnetic susceptibility and isothermal magnetization measurements reveal that CuTa₂O₆ is a new 1D Heisenberg magnet with predominant anti-ferromagnetic nearest-neighbor intrachain spin-exchange interaction of ∼50 K. Interchain exchange is a factor of ∼5 smaller. Heat capacity and low-temperature high-intensity neutron powder diffraction studies could not detect long-range order down to 0.45 K.

A Novel Gas Sensor Based on MgSb2O6 Nanorods to Indicate Variations in Carbon Monoxide and Propane Concentrations

Bystromite (MgSb₂O₆) nanorods were prepared using a colloidal method in the presence of ethylenediamine, after a calcination step at 800 °C in static air. From X-ray powder diffraction analyses, a trirutile-type structure with lattice parameters a = 4.64 Å and c = 9.25 Å and space group P4₂/mnm was identified. Using scanning electron microscopy (SEM), microrods with sizes from 0.2 to 1.6 μm were observed. Transmission electron microscopy (TEM) analyses revealed that the nanorods had a length of ~86 nm and a diameter ~23.8 nm. The gas-sensing properties of these nanostructures were tested using pellets elaborated with powders of the MgSb₂O₆ oxide (calcined at 800 °C) at temperatures 23, 150, 200, 250 and 300 °C. The pellets were exposed to different concentrations of carbon monoxide (CO) and propane (C₃H₈) at these temperatures. The results showed that the MgSb₂O₆ nanorods possess excellent stability and high sensitivity in these atmospheres.

Dynamic response of CoSb2O6 trirutile-type oxides in a CO2 atmosphere at low-temperatures

Experimental work on the synthesis of the CoSb₂O₆ oxide and its CO₂ sensing properties is presented here. The oxide was synthesized by a microwave-assisted colloidal method in presence of ethylenediamine after calcination at 600 °C. This CoSb₂O₆ oxide crystallized in a tetragonal structure with cell parameters a = 4.6495 and c = 9.2763 Å, and space group P4₂/mnm. To prove its physical, chemical and sensing properties, the oxide was subjected to a series of tests: Raman spectroscopy, Scanning Electron Microscopy (SEM) and impedance (Z) measurements. Microstructures, like columns, bars and hollow hemispheres, were observed. For the CO₂ sensing test, a thick film of CoSb₂O₆ was used, measuring the impedance variations on the presence of air/CO₂ flows (0.100 sccm/0.100 sccm) using AC (alternating current) signals in the frequency-range 0.1–100 kHz and low relative temperatures (250 and 300 °C). The CO₂ sensing results were quite good.

Enhanced photocatalytic activity of nanocrystalline N-doped ZnSb2O6: role of N doping, cation ordering, particle size and crystallinity

Nanocrystalline N-doped ZnSb₂O₆ is synthesized in a single step in single phasic form by a novel combustion method.

Raman spectroscopic study of the antimonate mineral roméite

Raman spectroscopy has been sued to study the antimony containing mineral roméite Ca(2)Sb(2)O(6)(OH,F,O) from three different origins. Roméite is a calcium antimonate mineral of the pyrochlore group. An intense Raman band at approximately 518 cm(-1) for roméite is assigned to the SbO nu(1) symmetric stretching mode and the band at 466 cm(-1) to the SbO nu(3) antisymmetric stretching mode. The Raman band at 303 cm(-1) is attributed to the OSbO bending mode. Some variation in band positions is observed and is attributed to the variation in composition between the three mineral samples.

Raman spectroscopic study of the antimony bearing mineral langbanite

Raman spectroscopy has been used to characterise the antimonate mineral langbanite (Mn, Ca, Fe)(4)(2+)(Mn(3+), Fe(3+))(9)Sb(5+)Si(2)O(24). The mineral is characterised by a series of peaks in the 850-1200 cm(-1) region. Raman bands observed at 872 and 897cm(-1) are assigned to SbO antisymmetric and symmetric stretching vibrations, respectively. Associated with the SbO units are the bands at 330, 351 and 386 cm(-1) attributed to OSbO bending modes. Four Raman bands observed at 964, 986, 1012 and 1034 cm(-1) are assigned to SiO stretching vibrations. The observation of multiple SiO Raman bands provides evidence for the non-equivalence of the SiO units in the langbanite structure. Associated with the SiO units are the Raman bands at 542, 558, 646 and 671 cm(-1) attributed to OSiO bending modes. Low intensity bands are observed at 1130, 1200, 1432, 1718 and 1947 cm(-1) and are probably associated with delta SbOH deformation modes. Raman bands are observed at 3076 and 3476 cm(-1) and are assigned to strongly bonded water molecules involved in the langbanite structure. A sharp Raman band at 3680 cm(-1) are assigned to OH stretching vibrations. Raman spectroscopy provides evidence for water and OH units in the structure of langbanite and brings the formula of the mineral into question.

Vibrational spectroscopic study of the antimonate mineral bindheimite Pb2Sb2O6(O,OH)

Raman spectroscopy complimented with infrared spectroscopy has been used to characterise the antimonate mineral bindheimite Pb(2)Sb(2)O(6)(O,OH). The mineral is characterised by an intense Raman band at 656 cm(-1) assigned to SbO stretching vibrations. Other lower intensity bands at 664, 749 and 814 cm(-1) are also assigned to stretching vibrations. This observation suggests the non-equivalence of SbO units in the structure. Low intensity Raman bands at 293, 312 and 328c m(-1) are assigned to the OSbO bending vibrations. Infrared bands at 979, 1008, 1037 and 1058 cm(-1) may be assigned to deltaOH deformation modes of SbOH units. Infrared bands at 1603 and 1640 cm(-1) are assigned to water bending vibrations, suggesting that water is involved in the bindheimite structure. Broad infrared bands centred upon 3250 cm(-1) supports this concept. Thus the true formula of bindheimite is questioned and probably should be written as Pb(2)Sb(2)O(6)(O,OH,H(2)O).