(HCOO)3. When the reaction time was prolonged to 20 min, the
typical XRD pattern indicates that the sample was almost
amorphous, but typical peaks indexed to Ce(HCOO)3 could still
be observed (marked with *). When the reaction time was further
prolonged to 40 min, it is worth noting that the peaks assigned to
the face-centered cubic phase of ceria, such as (111) and (200),
could be clearly seen from the XRD pattern, which suggests that
the transformation of Ce(HCOO)3 to CeO2 took place at this
stage. After 80 min, peaks indexed to the pure phase of ceria