Synthesis, X-ray crystallography and infrared absorption spectroscopy of EuAl₂Si₂O₈

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A polycrystalline EuAl₂Si₂O₈ was synthesized in a solid state at 1, 300°C and oxygen fugacities below 10^-6 atm. Crystals were grown from a melt of the polycrystalline EuAl₂Si₂O₈ at temperatures from 1, 590°C to 1, 380°C at the cooling rate of 1.5°/hour in the gas mixtures (CO₂/H₂=1). The single crystal was monoclinic, and indicated diffraction symmetry consistent with the space groups C2/m, Cm, and C2. The cell dimensions are: a = 8.341(2) Å; b = 12.972(2) Å; c = 7.112(2) Å;β = 115.50(2)°. This compound is the most similar to Sr-feldspar among the MAl₂Si₂O₈ feldspars (M: Ca, Sr, Ba, and Pb) in cell dimensions and infrared absorption spectrum.