The operation of solid oxide fuel cells (SOFCs) at intermediate temperatures (500-700 °C) promotes a rapid startup, operational stability, material stability, and use of costeffective gas sealing, and interconnecting materials. (Sr,Mg)doped LaGaO 3 materials (hereinafter LSGM) are nowadays widely known as promising solid electrolytes to be employed in intermediate temperature SOFCs (IT-SOFCs) or in high temperature solid oxide electrolyzer cells (SOECs) [1]. Indeed, they have high oxygen ionic conductivity and stability over a wide range of oxygen partial pressures (P O 2 = 10 -22 to 1 atm), but also little or no electronic conduction to minimize leakage currents [2,3].
Early works on LaGaO 3 -based electrolytes were conducted by Ishihara et al. [4]. They found that doping Sr and Mg for La and Ga sites, respectively, could increase the conductivity of LaGaO 3 . As an example, La 0.9 Sr 0.1 Ga 0.8 Mg 0.2 O 3-d showed conductivity higher than conventional YSZ and ScSZ ionic electrolytes at intermediate temperatures. Afterwards, Huang and Goodenough [5] reported that La 0.80 Sr 0.20 Ga 0.83 Mg 0.17 O 3-d (hereinafter LS 0.20 GM 0.17 ) showed oxygen-ion conductivity values of 0.17, 0.08, and 0.03 S cm -1 at 800, 700, and 600 °C, respectively, exceeding values of YSZ material at the same temperatures (0.05 S cm -1 at 800 °C) [6]. Therefore, LSGM materials resulted to be potential candidate electrolytes for 8].
It is worth highlighting that the conductivity of LSGM materials often depends on the synthesis methods, due to different grain size, grain boundaries, and secondary phases formation. In fact, various intermediate phases, such as LaSrGaO 4 , LaSrGa 3 O 7 , La 4 Ga 2 O 9 , and MgO, are frequently formed [9][10][11][12][13]. However, the synthesis of LS 0.20 GM 0.17 seems