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.

Experimental work on the synthesis of the CoSb 2 O 6 oxide and its CO 2 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 CoSb 2 O 6 oxide crystallized in a tetragonal structure with cell parameters = 4.6495 and = 9.2763 Å, and space group P4 2 /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 CO 2 sensing test, a thick film of CoSb 2 O 6 was used, measuring the impedance variations on the presence of air/CO 2 flows (0.100 sccm/0.100 sccm) using AC (alternating current) signals in the frequency-range OPEN ACCESSSensors 2014, 14 15803 0.1-100 kHz and low relative temperatures (250 and 300 °C). The CO 2 sensing results were quite good.

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Micro-and nanoparticles of NiSb 2 O 6 were synthesized by the microwave-assisted colloidal method. Nickel nitrate, antimony chloride, ethylenediamine, and ethyl alcohol were used. The oxide was obtained at 600 ∘ C and was analyzed by X-ray diffraction (XRD) and Raman spectroscopy, showing a trirutile-type structure with cell parameters = 4.641Å, = 9.223Å, and a space group P4 2 /mnm (136). Average crystal size was estimated at ∼31.19 nm, according to the XRD-peaks. The microstructure was scrutinized by scanning electron microscopy (SEM), observing microrods measuring ∼3.32 m long and ∼2.71 m wide, and microspheres with an average diameter of ∼8 m; the size of the particles shaping the microspheres was measured in the range of ∼0.22 to 1.8 m. Transmission electron microscopy (TEM) revealed that nanoparticles were obtained with sizes in the range of 2 to 20 nm (∼10.7 nm on average). Pellets made of oxide's powders were tested in propane (C 3 H 8 ) and carbon monoxide (CO) atmospheres at different concentrations and temperatures. The response of the material increased significantly as the temperature and the concentration of the test gases rose. These results show that NiSb 2 O 6 may be a good candidate for gas sensing applications.

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ZnSb2O6has been synthesized by a microwave-assisted solution method in order to test its possible application as a gas sensor. Zinc nitrate, antimony trichloride, and ethylenediamine were used as precursors and deionized water as solvent. Microwave radiation, with a power of ~350 W, was applied for solvent evaporation. The thermal decomposition of the precursors leads to the formation of ZnSb2O6at 600°C. This oxide crystallized in a tetragonal structure with cell parametersa=4.66 Å,c=9.26 Å and space groupP42/mnm. Microwires and microrods formed by nanocrystals were observed by means of scanning and transmission electron microscopies (SEM and TEM, resp.). Pellets of the oxide were tested as gas sensors in flowing atmospheres of carbon monoxide (CO) and propane (C3H8). Sensitivity increased with the gas concentration (0–300 ppm) and working temperatures (ambient, 150 and 250°C) increase. The results indicate high sensitivity of ZnSb2O6in both gases at different concentrations and operating temperatures.