Co-precipitation in aqueous medium of La0.8Sr0.2Ga0.8Mg0.2O3−δ via inorganic precursors

A simple and inexpensive co-precipitation route in aqueous medium is proposed to prepare La0.8Sr0.2Ga0.8Mg02O3−δ ionic conductor (LSGM). Different synthetic procedures and operating parameters (i.e. nature and amount of the precipitating agents, HNO3 addition and temperature) have been evaluated in order to underline their influence on the composition and microstructure of the final phase. Intermediate and final products were characterized by Thermal-Gravimetry, IR-spectroscopy, X-ray Powder Diffraction, Rietveld analysis and Scanning Electron Microscopy. The electrical properties were measured by Impedance Spectroscopy in the temperature range 250–800 °C. Slight variations of the synthetic procedure (such as precipitating agent amount or no HNO3 addition) have a considerable and detrimental effect on the ions losses and the subsequent achievement of the final phase. The use NH4OH as an alternative precipitating agent is dramatically disadvantageous. Ions losses during precipitation must be controlled (i) to avoid understoichiometry in the LSGM phase and (ii) to prevent the formation of large amounts of secondary phases. In fact, both affect the total electrical conductivity.The use of large excess of (NH4)2CO3 precipitating agent and the addition of HNO3 lead to the best material characterized by a rhombohedral structure, small amount of side phases, a relative density of 98% and a total conductivity of 6.44 × 10−2 S cm−1 at 800 °C and 1.13 × 10−2 S cm−1 at 600 °C.