On the crystal chemistry and stability of Sm2+ in SmSO4 and solid solutions of M1-xSmxSO4 (M = Ba, Sr)

Solid solution formation of Sm2+ and MSO4 (M = Sr, Pa) was investigated for syntheses using (i) a LiCl high-temperature solution exposed to a reducing atmosphere and (ii) precipitation reactions at room temperature starting f rom aqueous solutions of SmI2 or electrochemically gained Sm2+. In contrast to (ii), present results show that a high-temperature approach (i) yielded only a very low amount of Sm2+ in M1-xSmxSO4. Formation of solid solution system (0<x<1) was confirmed for Sr1-xSmxSO4 and Ba1-xSmxSO4 by X-ray powde r diffraction analysis and optical lifetime measurements. The unit cell par ameters of Ba1-xSmxSO4 showed a slight deviation from Vegard's law. Positiv e and negative deviations are in agreement with results on solid solutions of Ba1-xSrxSO4. Compounds obtained by syntheses at room temperature were ex posed to annealing at 450 to 850 degreesC using a reducing or oxidizing atm osphere. In this temperature range, M1-xSmxSO4 (M = Sr, Pa) decomposed into Sm2O2(SO4) and the corresponding MSO4. Solid solutions of M1-xSmxSO4 (M = Pa, Sr) represent a new system for investigating Sm2+ in an oxide environme nt. There are only a few other oxide host lattices stabilizing divalent sam arium. (C) 2000 Academic Press.