ChemInform Abstract: Phase Transition and Thermal Expansion of Ho₂W₃O₁₂.

Abstract

Polycrystalline Ho2W3O12 is prepared by calcination of stoichiometric amounts of Ho2O3 and WO3 in air (1100 °C, 10 h) with different cooling treatments (850 °C plus furnace cooling or 1100 °C plus quenching in H2O) to probe the relationship between phase formation and preparative conditions.

Negative and Near-Zero Thermal Expansion in A2M3O12 and Related Ceramic Families: A Review

“…Water molecules likely interact with the framework through hydrogen bonding and it has been proposed that the oxygen atoms from water molecules intact with A 3+ or M 6+ , while hydrogen atoms from water molecules interact with the framework 2-fold oxygens (Wu et al, 2016). These interactions between water molecules and the framework can cause amorphization in molybdates and tungstates (Marinkovic et al, 2005;Yu et al, 2008;Li et al, 2012) or even change the crystal symmetry in some tungstates (Kol'tsova, 2001;Sleight, 2003;Cao et al, 2016;Pontón et al, 2017;Machado et al, 2021). Symmetry lowering by transformation to the monoclinic phase, or the presence of water molecules in channels, will inhibit, or attenuate, the asymmetrical framework librations of the quasi-rigid polyhedra, due to freezing of polyhedra rocking motions or due to steric effects, respectively.…”