SIZE-INDUCED STRUCTURAL TRANSITIONS IN THE CU-O AND CE-O SYSTEMS

We have studied the effect of reducing the particle size on the crysta l structures of copper oxide and cerium oxide. Below 25 nm, the cubic Cu2O is found to be more stable than the monoclinic CuO. This confirms an earlier conjecture that the ionic character of a solid tends to in crease with a reduction in the particle size. As a result, high-symmet ry crystal structures are more likely to be stable at smaller sizes. F or cerium oxide, the bulk (cubic) CeO2 phase remains stable down to 4. 8 nm and, as expected, does not undergo a transition to any of the oth er available structures with lower symmetry.