## Electrical Response of the Spinel ZnAl2O4 and Its Application in the Detection of Propane Gas  
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Mg\({}^{2+}\), Mn\({}^{2+}\), Co\({}^{2+}\), and Ni\({}^{2+}\). M can be substituted for the trivalent cations Cr\({}^{3+}\), Ga\({}^{3+}\), and Fe\({}^{3+}\)[2]. These compounds show interesting physical (such as magnetic and refractory) and chemical properties that make them suitable for several technological applications [3; 4; 5]. Moreover, they possess high resistance to acids, high melting points, relatively high surface areas, and good catalytic properties [1]. The good properties of these materials are due mainly to the nanometric size of their particles [6]. Wet chemistry methods are employed for obtaining particle sizes of less than 100 nm from spinel-type materials [3], since it allows the control of the physical and chemical parameters involved during the synthesis process [2; 3; 7]. The ZnAl\({}_{2}\)O\({}_{4}\) is a spinel-type ternary compound [1; 2; 8], a ceramic semiconductor material with a bandgap of 3.5-3.9 eV [9; 10]. According to the literature, ZnAl\({}_{2}\)O\({}_{4}\) can be adjusted to the aluminates' formula XAl\({}_{2}\)O\({}_{4}\)[5; 11], where X is replaced by the divalent cation Zn\({}^{2+}\)[3; 5]. However, it can also be substituted for the divalent ions Co\({}^{2+}\), Ni\({}^{2+}\), and Cu\({}^{2+}\)[6]. The material typically has a crystalline phase with a cubic-type crystallographic system with space group Fd-3m [3; 10; 12]. It has been intensively studied due to its attractive properties, such as high thermal stability, low-temperature sinterability, low surface acidity, good diffusion, and high quantum yields [13], which have promoted its technological application in different fields. These applications include optical coatings, photo-electronic devices, display technologies, ceramics, and sensors [1; 9; 14]. Some reports have stated that the ZnAl\({}_{2}\)O\({}_{4}\) possesses high sensitivity, good linearity, small hysteresis, and short response and recovery times in humid [9] and propane [1] atmospheres, which is attributed to the porosity and the nanostructures (such as nanorods) obtained during the compound's synthesis [9]. The goal now is to apply new materials (such as the semiconductors) to toxic gas detection systems [15; 16; 17]. These devices are intended to provide safe zones for humans in C\({}_{3}\)H\({}_{8}\), CO, or CO\({}_{2}\) atmospheres, among others [18; 19; 20]. Our proposed detector consists of two essential parts: the sensor and the electronic circuit. The sensor detects the chemical \"signals\" (reactions) of the gases. Analog or digital, the electronic circuit transforms the chemical signal into an electrical signal and records it.