## 4 Conclusions  
The synthesis of NiSb\({}_{2}\)O\({}_{6}\) powders was conducted successfully by means of a wet chemistry process assisted with microwave radiation. This method allowed us to obtain different morphologies for use as a gas sensor (in this work: CO and propane). Using UV-Vis, forbidden bandgap values of \(\sim\)3.06, \(\sim\)3.14, and \(\sim\)3.25 eV were estimated for the powders of NiSb\({}_{2}\)O\({}_{6}\) calcined at 700, 800, and 900 \({}^{\circ}\)C, respectively. It was observed that the bandgap value was closely related to the crystallite size (\(\sim\)32, \(\sim\)40, and \(\sim\)44 nm at 700,  
Figure 11: (**a**) Bode diagram of NiSb\({}_{2}\)O\({}_{6}\) pellets’ behavior, (**b**) electronic diagram of the C\({}_{3}\)H\({}_{8}\)-detector, (**c**) detector’s principle of operation.  
800, and 900 \({}^{\circ}\)C, respectively) and the calcination temperature in the synthesis process. By means of scanning electron microscopy (SEM), microstructures in the form of polyhedra and irregular particles of different sizes, distributed over the entire surface of the material, were observed. This was largely due to the chelating agent (ethylenediamine), the heat treatment, and the synthesis method. In static and dynamic tests using pellets made with powders of the oxide, a good response was obtained at different concentrations and flows of CO and operating temperatures, obtaining a maximum sensitivity of ~72.4 at 300 ppm of CO and 300 \({}^{\circ}\)C. In dynamic tests conducted using thick films prepared with the material's powders, an excellent response was obtained at 360 \({}^{\circ}\)C in 600 ppm of propane and applying an alternating current (at 0.1 and 1 kHz). Good stability, reproducibility, performance, and short response and recovery times were found. The excellent material's dynamic response in propane allowed us to design an efficient prototype for detecting atmospheres of such gas at different working frequencies. The synthesis method used and the high material's crystallinity contributed greatly to obtaining excellent results in the CO and propane detection tests; therefore, we can affirm that NiSb\({}_{2}\)O\({}_{6}\) calcined at 900 \({}^{\circ}\)C is a strong candidate for being applied as a gas detector.  
Formal analysis, [PERSON]-[PERSON] and [PERSON]-[PERSON]; investigation, [PERSON]-[PERSON] and [PERSON]-[PERSON]; methodology, [PERSON]-[PERSON], [PERSON]-[PERSON], [PERSON]-[PERSON], [PERSON]-[PERSON], [PERSON]-[PERSON], [PERSON] and [PERSON]; project administration, [PERSON]-B.; resources, [PERSON]-B. and [PERSON]-A.; supervision, [PERSON]-B.; validation, [PERSON]-B.; visualization, [PERSON]-B. and [PERSON]-[PERSON]; writing--original draft, [PERSON]-[PERSON], [PERSON]-B., [PERSON]-[PERSON], [PERSON], [PERSON], [PERSON], [PERSON], [PERSON] and [PERSON]; writing--review and editing, [PERSON] and [PERSON]. All authors have read and agreed to the published version of the manuscript.  
This research was funded by the National Council of Science and Technology of Mexico (CONACYT), grant number 888575.  
Not applicable.  
The data that support the findings of this study are available from the corresponding authors upon request.  
[PERSON] thanks CONACyT for a scholarship. Likewise, we thank [PERSON], [PERSON], [PERSON], [PERSON], and [PERSON] for their technical assistance. This work was conducted following the research guidelines for \"Nanostructured Semiconductor Oxides\" of the CUCEI's UDG-CA-895 \"Nanostructured Semiconductors\" academic group, University of Guadalajara.  
The authors declare no conflict of interest.