Confined growth of Eu2O3 nanocrystals in a new polymorph in amorphous mesoporous Al2O3

Abstract Eu2O3 in divided groups in pores in a mesoporous Al2O3 (amorphous) has a confined growth in nanocrystals (average, 30 nm diameter) in a new polymorph of R3c hexagonal crystal structure with lattice parameters a = 0.5468 nm and c = 1.6950 nm. This occurs on reacting dispersed Eu3+ cations (in water) with a mesoporous AlO(OH) · α2O powder. A pore incorporates Eu3+ cations in a confined group depending on its size and governs controlled Eu2O3 nucleation and growth in a self-confined dimension in a nanocrystal. This new lattice involves a 5.60, 2.99 and 1.03 times larger volume V 0, enclosed in a reduced S 0 = 5.41 nm2 surface per unit volume relative to 9.27, 9.28 and 5.52 nm2, in the bulk hexagonal Eu2O3, monoclinic Eu2O3 and cubic Eu2O3 polymorphs respectively. From the pressure–volume isotherm, the large V 0 implies that it grows quickly under the influence of a reduced effective pressure in the pores so that it balances the ▵P → 0 pressure gradient as early as possible. The results are discussed with a proposed model of nucleation and growth in a self-confined dimension under the influence of a reduced pressure.