Defining the Structural Stability Field of Disordered Fluorite Oxides

Fluorite-structured oxides constitute an important class of materials for energy technologies. Despite their high level of structural symmetry and simplicity, these materials can accommodate atomic disorder without losing crystallinity, making them indispensable for uses in environments with high temperature, changing chemical compositions, or intense radiation fields. In this contribution, we present a set of simple rules that predict whether a compound may adopt a disordered fluorite structure. This approach is closely aligned with Pauling’s rules for ionic crystal structures and Goldschmidt’s rules for ionic substitution.

Chemical bonding and Born charge in 1T-HfS2

We combine infrared absorption and Raman scattering spectroscopies to explore the properties of the heavy transition metal dichalcogenide 1T-HfS2. We employ the LO–TO splitting of the Eu vibrational mode along with a reevaluation of mode mass, unit cell volume, and dielectric constant to reveal the Born effective charge. We find $${Z}_{{\rm{B}}}^{* }$$ Z B * = 5.3e, in excellent agreement with complementary first-principles calculations. In addition to resolving the controversy over the nature of chemical bonding in this system, we decompose Born charge into polarizability and local charge. We find α = 5.07 Å3 and Z* = 5.2e, respectively. Polar displacement-induced charge transfer from sulfur p to hafnium d is responsible for the enhanced Born charge compared to the nominal 4+ in hafnium. 1T-HfS2 is thus an ionic crystal with strong and dynamic covalent effects. Taken together, our work places the vibrational properties of 1T-HfS2 on a firm foundation and opens the door to understanding the properties of tubes and sheets.

Competing hydrogen-bonding interactions in a high-Tc organic molecular-ionic crystal with evident nonlinear optical response

An organic molecular-ionic crystal of (TPPO–H)2SO4 exhibits moderate NLO response which is twice that of KDP and competing hydrogen-bonding interactions triggered high-Tc phase transition.

Polyoxometalate based ionic crystal: dual applications in selective colorimetric sensor for hydrated ZnCl2 and antimicrobial activity

One-pot synthesis of POM-salt ([Himi]4[SiMo12O40] (1)) was achieved by mixing silicomolybdic acid and imidazole in acidic conditions and characterized by FTIR, TGA, SEM, EDX, ICP-OES and XPS.