Structure, thermostability and magnetic properties of cubic Ce2-x Ti2O7 pyrochlore obtained via sol-gel preparation.

ABSTRACT

Lanthanum-based titanates have been attracting considerable interest by virtue of their structural operability and hence diverse physical properties. The preparation of lanthanum-based titanates with novel crystal structure is a fascinating task. In this work, we report the preparation of a cubic Ce2-x Ti2O7 pyrochlore using the sol-gel method. The crystal structure, thermostability and magnetism were studied via the temperature dependence of X-ray powder diffraction, X-ray photoelectron spectroscopy and magnetization measurements. It has been revealed that the as-prepared Ce2-x Ti2O7 pyrochlore possesses a cubic symmetry (space group Fd3̄m), however there is an 18(1)% vacancy of Ce ions in the as-prepared samples. No distinct phase transition and thermal expansion anomaly were observed in the investigated temperature range from 300 K to 700 K. Intriguingly, lattice defects may favor the transformation of Ce valence from +3 to +4 and an unusual weak magnetic ordering state emerged up to 400 K. The persistence of magnetism at such high temperatures is rare and mysterious for cerium titanates. Our findings provide the possibility of adjusting the crystal structure and magnetic properties of cerium titanates, anticipated to the development of lanthanum-based oxides.