Modifying the hygroscopic property of La2O3 by Pr, Sm and Nd doping

Combustion synthesized La<inf>2</inf>O<inf>3</inf>, La<inf>2-2x</inf>Pr<inf>2x</inf>O<inf>3</inf> (x = 0.025–0.30), La<inf>2-2x</inf>Nd<inf>2x</inf>O<inf>3</inf> (x = 0.025–0.50), La<inf>2-2x</inf>Sm<inf>2x</inf>O<inf>3</inf> (x = 0.025–0.30) and their subsequently formed hydroxide phases were characterized by X-ray diffraction (XRD) and Fourier transform infrared spectroscopy (FTIR). The hydroxylation reaction (hygroscopic property) of oxides in an open atmosphere was monitored by X-ray diffraction (XRD). All of these oxides hydroxylate to form stable hydroxides at room temperature upon exposure to open atmosphere for certain interval of time. La<inf>2</inf>O<inf>3</inf> shows rapid hydroxylation reaction as compared to other oxides (La<inf>2-2x</inf>M<inf>2x</inf>O<inf>3</inf>, M = Pr, Nd, Sm). It is observed that La<inf>2-2x</inf>Pr<inf>2x</inf>O<inf>3</inf> shows the slowest hydroxylation reaction compared to La<inf>2-2x</inf>Nd<inf>2x</inf>O<inf>3</inf> and La<inf>2-2x</inf>Sm<inf>2x</inf>O<inf>3</inf>. Further, as the concentration of dopant ion concentration increases in each La<inf>2-2x</inf>Pr<inf>2x</inf>O<inf>3</inf> (x = 0.05, 0.15 and 0.30), La<inf>2-2x</inf>Nd<inf>2x</inf>O<inf>3</inf> (x = 0.05, 0.15, 0.30 and 0.50) and La<inf>2-2x</inf>Sm<inf>2x</inf>O<inf>3</inf> (x = 0.05, 0.15 and 0.30), the hydroxylation reaction becomes slower consecutively. Overall, 30% Pr doped La<inf>2</inf>O<inf>3</inf> (La<inf>1.40</inf>Pr<inf>0.60</inf>O<inf>3</inf>) shows the highest stability (slowest rate of hydroxylation) in open atmosphere at room temperature.