Self-propagating room temperature synthesis and structural characterization of transition metal-rare earth based compositionally complex oxides

Two compositionally complex oxides (CCOs) of the type (Hf_0.2Zr_0.2Ce_0.2Gd_0.2 RE_0.2)O_2-δ, were synthesized via self-propagating room temperature synthesis where RE=Yb for one of the two, while in the other case, Yb was replaced by equal concentrations of Pr and Nd. Heat-treatment at varied temperatures between 900 °C – 1500 °C and phase evolution studies revealed the formation of a single phase with a FCC structure with the Yb containing oxide. However, the substitution of Yb with Pr and Nd resulted in an additional secondary FCC phase. Furthermore, Raman spectroscopy confirmed pyrochlore-type ordering in both compounds with exemplification of superlattice planes in high-resolution transmission electron microscopic images. The presence of 3+ and 4+ cations confirmed by X-ray photoelectron spectroscopy, is in accordance with the results on the pyrochlore structure containing two different cationic species.