Ba3(Cr0.97(1)Te0.03(1))2TeO9: in Search of Jahn-Teller Distorted Cr(II) Oxide

Heteroepitaxial Growth of B5 -Site-Rich Ru Nanoparticles Guided by Hexagonal Boron Nitride for Low-Temperature Ammonia Dehydrogenation

Ruthenium is one of the most active catalysts for ammonia dehydrogenation and is essential for the use of ammonia as a hydrogen storage material. The B₅ -type site on the surface of ruthenium is expected to exhibit the highest catalytic activity for ammonia dehydrogenation, but the number of these sites is typically low. Here, a B₅ -site-rich ruthenium catalyst is synthesized by exploiting the crystal symmetry of a hexagonal boron nitride support. In the prepared ruthenium catalyst, ruthenium nanoparticles are formed epitaxially on hexagonal boron nitride sheets with hexagonal planar morphologies, in which the B₅ sites predominate along the nanoparticle edges. By activating the catalyst under the reaction condition, the population of B₅ sites further increases as the facets of the ruthenium nanoparticles develop. The electron density of the Ru nanoparticles also increases during catalyst activation. The synthesized catalyst shows superior catalytic activity for ammonia dehydrogenation compared to previously reported catalysts. This work demonstrates that morphology control of a catalyst via support-driven heteroepitaxy can be exploited for synthesizing highly active heterogeneous catalysts with tailored atomic structures.

Interacting Quantum Atoms Method for Crystalline Solids

An implementation of the Interacting Quantum Atoms method for crystals is presented. It provides a real space energy decomposition of the energy of crystals in which all energy components are physically meaningful. The new package ChemInt enables one to compute intra-atomic and inter-atomic energies, as well as electron population measures used for quantitative description of chemical bonds in crystals. The implementation is tested and applied to characteristic molecular and crystalline systems with different types of bonding.

First-principles investigation of the ferroelectric, piezoelectric and nonlinear optical properties of LiNbO3-type ZnTiO3

The newly synthesized LN-type ZnTiO₃ (J. Am. Chem. Soc. 2014, 136, 2748) contains cations with the electronic configurations nd¹⁰ (Zn²⁺: 3d¹⁰) along with second-order Jahn-Teller (SOJT) nd⁰ (Ti⁴⁺: 3d⁰) cations. This is different from traditional ferroelectrics with the electric configurations of d⁰ transition metal ions or/and lone pair electrons of ns². Using a first-principles approach based on density functional theory, we investigate the electronic structure, zone-center phonon modes, piezoelectric and nonlinear optical properties of the LiNbO₃-type ZnTiO₃. The electronic structure indicates that this compound is a wide direct-band-gap insulator. The results reveal that this compound is a good ferroelectric material with a large spontaneous polarization of 90.43μC/cm². The Raman scattering peaks of A₁ and E modes are assigned to their zone-center optical modes. Additionally, the large piezoelectric and nonlinear optical susceptibilities reveal that LiNbO₃-type ZnTiO₃ is a high-performance lead-free piezoelectric and nonlinear optical crystal.

Crystal structures of the triple perovskites Ba2K2Te2O9 and Ba2KNaTe2O9, and redetermination of the double perovskite Ba2CaTeO6

Single crystals of Ba2K2Te2O9 (dibarium dipotassium nona-oxidoditellurate), (I), Ba2KNaTe2O9 (dibarium potassium sodium nona-oxidoditellurate), (II), and Ba2CaTeO6 (dibarium calcium hexa-oxidotellurate), (III), were obtained from KNO3/KI or KNO3/NaNO3 flux syntheses in platinum crucibles for (I) and (II), or porcelain crucibles for (III). (I) and (II) are isotypic and are members of triple perovskites with general formula A2[12co]A'[12co]B2[6o]B'[6o]O9. They crystallize in the 6H-BaTiO3 structure family in space-group type P63/mmc, with the A, A', B and B' sites being occupied by K, Ba, Te and a second Ba in (I), and in (II) by mixed-occupied (Ba/K), Ba, Te and Na sites, respectively. (III) adopts the A2[12co]B'[6o]B''[6o]O6 double perovskite structure in space-group type Fmm, with Ba, Ca and Te located on the A, B' and B'' sites, respectively. The current refinement of (III) is based on single-crystal X-ray data. It confirms the previous refinement from X-ray powder diffraction data [Fu et al. (2008). J. Solid State Chem.181, 2523-2529], but with higher precision.