Structure and phase stability of nanocrystalline Ce1-x Ln (x) O2-x/2-delta (Ln = Yb, Lu) in oxidizing and reducing atmosphere

摘要

The structure and phase evolution of nanocrystalline Ce1- x Ln (x) O2- x/2-delta (Ln = Yb, Lu, x = 0 - 1) oxides upon heating in H-2 was studied for the first time. Up to 950 A degrees C the samples were single-phase, with structure changing smoothly with x from fluorite type (F) to bixbyite type (C). For the Lu-doped samples heated at 1100 A degrees C in the air and H-2, phase separation into coexisting F- and C-type structures was observed for similar to 0.40 < x < similar to 0.70 and similar to 0.25 < x < similar to 0.70, respectively. It was found also that addition of Lu3+ and Yb3+ strongly hinders the crystallite growth of ceria during heat treatment at 800 and 950 A degrees C in both atmospheres. Valency of Ce and Yb in Ce0.1Lu0.9O1.55-delta and Ce0.95Yb0.05O1.975-delta samples heated at 1100 A degrees C was studied by XANES and magnetic measurements. In the former Ce was dominated by Ce4+, with small contribution of Ce3+ after heating in H-2. In the latter, Yb existed exclusively as 3+ in both O-2 and H-2.