Metastable Crystal Structure of Strontium- and Magnesium-Substituted LaGaO3
The metastable crystal structure of strontium- and magnesium-substituted LaGaO3 (LSGM) was studied at room and intermediate temperatures using powder X-ray diffractometry and Rietveld refinement analysis. With increased strontium and magnesium content, phase transitions were found to occur from orthorhombic (space group Pbnm) to rhombohedral (space group R[Threemacr]c) at the composition La0.825Sr0.175Ga0.825Mg0.175O2.825 and, eventually, to cubic (space group Pm[Threemacr]m) at the composition La0.8Sr0.2Ga0.8Mg0.2O2.8. At 500°C in air and at constant strontium and magnesium content, a phase transformation from orthorhombic (space group Pbnm) to cubic (space group Pm[Threemacr]m) was observed. For the orthorhombic modification, thermal expansion coefficients were determined to be αa,ortho = 10.81 × 10−6 K−1, αb,ortho = 9.77 × 10−6 K−1, and αc,ortho = 9.83 × 10−6 K−1 (25°–400°C), and for the cubic modification to be αcubic= 13.67 × 10−6 K−1 (500°–1000°C).
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