Ceramics of the melilite‐type compound La1+xSr1−xGa3O7−δ were prepared by conventional ceramic processing. Samples prepared represented the entire homogeneity region of the phase (i.e., x=−0.15 to 0.60). Electrochemical characterization under variable temperature and atmospheric conditions in the vicinity of air entailed four‐point direct‐current conductivity measurements and electromotive force measurements. La1+xSr1−xGa3O7−δ samples exhibited a p‐type behavior with generally increased conductivity with increased substitution of lanthanum for strontium, which reached a saturation value of ∼10−1 S·cm−1 at 950°C.

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Ceramic samples of the melilite‐type La1+xSr1–xGa3O7–δ (x=−0.15 to 0.60) compound were prepared by conventional ceramic processing. Sintering characteristics and microstructural evolution were studied. A phase diagram study was performed to establish the solid solubility limits as a function of the La:Sr ratio. Structural investigations of the Dalton composition as well as strontium‐ and lanthanum‐rich samples entailed X‐ray, neutron, and electron diffraction techniques at ambient and elevated temperatures. The homogeneity region was remarkably broad (x=−0.15 to 0.60) with no changes in space group observed. A small shrinkage of the unit cell was found with increased lanthanum content. Phase transitions at ambient and intermediate temperatures did not occur.

The ternary systems La2O3–SrO–Ga2O3, La2O3–MgO–Ga2O3, and SrO–MgO–Ga2O3 were studied at 1400°C in air, with emphasis on LaGaO3. The compound exhibited a small solid solubility of strontium substituting for lanthanum and also of magnesium substituting for gallium. In the system La2O3–SrO–Ga2O3, LaGaO3 existed only within a very narrow concentration region, whereas in the system La2O3–MgO–Ga2O3, LaGaO3 was in equilibrium with most of the phases of the system. The system SrO–MgO–Ga2O3 at 1400°C in air was characterized by an extended liquid phase at ∼1185°C.