High-temperature X-ray diffraction and specific heat studies on GdAlO3, Gd3Al5O12 and Gd4Al2O9

Gadolinium aluminates, GdAlO3, Gd3Al5O12 and Gd4Al2O9 were synthesized by the solution combustion method. Very fine particles in the nanoparticle range of ∼10–20 nm could be prepared by this method as evidenced by surface area measurement by multipoint BET method. Thermal studies on these compounds were carried out using high-temperature X-ray diffraction (HT-XRD) and differential scanning calorimetry (DSC) methods. The thermal expansion coefficients of GdAlO3, Gd3Al5O12 and Gd4Al2O9 were calculated from the lattice parameter data and specific heats were calculated from DSC data. The lattice parameters of GdAlO3 and Gd3Al5O12 were found to increase linearly with temperature whereas Gd4Al2O9 did not show a linear trend. The specific heats of these compounds show an increasing trend with increase in aluminum atom fraction. Based on the thermodynamic data available in the literature and the specific heat data obtained in this study, oxygen potential diagram was constructed at 1000 K.