A Limiting Current Oxygen Sensor Based on LSGM as a Solid Electrolyte and LSGMN (N = Fe, Co) as a Dense Diffusion Barrier

The La_0.8Sr_0.2(Ga_1−x Co _x )_0.8Mg_0.2O_3−δ (LSGMC x = 0.05, 0.1, 0.15, 0.2, 0.25) and La_0.8Sr_0.2(Ga_1−x Fe _x )_0.8Mg_0.2O_3−δ (LSGMF x = 0.1, 0.2, 0.3) samples were prepared by solid-state reaction. The structure, conductivity, thermal expansion behavior, and chemical compatibility were studied by XRD, dilatometry, and four-terminal method. A limiting current oxygen sensor was prepared with La_0.8Sr_0.2Ga_0.83Mg_0.17O_2.815 as a solid electrolyte and La_0.8Sr_0.2(Ga_0.75Co_0.25)_0.8Mg_0.2O_3−δ as a dense diffusion barrier. The oxygen-sensitive characteristic was measured at different oxygen concentrations. The results show that the phase structure of samples is cubic, except La_0.8Sr_0.2(Ga_0.75Co_0.25)_0.8Mg_0.2O_3−δ , which has a hexagonal structure. The change in activation energy for electrical conductivity and the increase in thermal expansion coefficient are confirmed to correlate with an increasing concentration of oxygen vacancies. The limiting current oxygen sensor exhibits a good limiting current platform and the limiting current depends linearly on the oxygen concentration: I _L(mA) = 12.8519 + 2.2667 \(x_{{\text{O}_{\text{2}} }}\) (mol%, 0 < \(x_{{{\text{O}}_{ 2} }}\) < 3.31) at 750 °C, I _L(mA) = 14.3222 + 3.5180 \(x_{{\text{O}_{\text{2}} }}\) (mol%, 0 < \(x_{{{\text{O}}_{ 2} }}\) < 4.16) at 800 °C, and I _L(mA) = 15.2872 + 5.0269\(x_{{\text{O}_{\text{2}} }}\)(mol%, 0 < \(x_{{{\text{O}}_{ 2} }}\) < 4.12) at 850 °C. The sensor has the best sensitivity at 850 °C. As the oxygen concentration increases, the interface resistance of the sensor decreases at 850 °C.