Synthesis, crystal structure, spectroscopic properties, and thermal behavior of rare-earth oxide selenates, Ln2O2SeO4 (Ln = La, Pr, Nd): The new perspectives of solid-state double-exchange synthesis

Abstract

Three rare-earth oxide selenates Ln2O2SeO4 (Ln = La, Pr, Nd) have been prepared via double-exchange solid-state reactions between respective LnOCl oxyhalides and potassium selenate. This approach succeeded to obtain singlephase specimens of La2O2SeO4 and Nd2O2SeO4, previously known as transients upon thermal decomposition of the corresponding selenates, as well as a new compound Pr2O2SeO4. Refinement of their crystal structures from powder X-ray diffraction data confirmed previous attributions to the grandreefite (Pb2F2SO4) structure type observed also for the Ln2O2SO4 oxide sulfates. According to polythermic X-ray studies, La2O2SeO4 is stable until at least 700 C. All compounds were characterized by infrared and X-ray photoelectron spectroscopy.