Publications by authors named "R Niewa"

From reaction of excess lithium with tin, we isolate well-crystallized LiSn and solve the crystal structure from single-crystal X-ray diffraction data. The orthorhombic structure (space group ) features the same coordination polyhedra around tin and lithium as previously predicted by electronic structure calculations for this composition, however differently arranged. An extensive analysis, including thermodynamic integration using Langevin dynamics in combination with a machine-learning potential (moment tensor potential), is conducted to understand the thermodynamic stability of this LiSn structure observed in our experiments.

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The first nitridogermanates(III) Ca [Ge N ] and Sr [Ge N ] were synthesized from sodium flux and structurally characterized by powder and single crystal X-ray diffraction, respectively. They crystallize isostructurally to each other and homeotypic to Ca [Cr N ]H in space group R . They feature unprecedented, mutually isolated, ethane-like [Ge N ] anions in a staggered conformation.

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A novel type of sub-lattice of the Jahn-Teller (JT) centers was arranged in Ti-doped barium hexaferrite BaFeO. In the un-doped crystal all iron ions, sitting in five different crystallographic positions, are Fe in the high-spin configuration (S = 5/2) and have a non-degenerate ground state. We show that the electron-donor Ti substitution converts the ions to Fe predominantly in tetrahedral coordination, resulting in doubly-degenerate states subject to the [Formula: see text] problem of the JT effect.

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Single crystals of aluminum substituted strontium hexaferrite SrFeAlO were grown from sodium oxide based flux. The substitution level aimed for was = 1.2.

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Solutions of gallium trihalides GaX (X=F, Cl, Br, I) and their ammoniates in liquid ammonia were studied at ambient temperature under autogenous pressure by multinuclear ( Ga, Cl, Br) NMR spectroscopy. To unravel the role of pH, the analyses were done both in absence and in presence of ammonium halides, which are employed as mineralizers during ammonoacidic gallium nitride crystal growth. While gallium trifluoride and its ammoniate were found to be too sparingly soluble to give rise to a NMR signal, the spectra of solutions of the heavier halides reveal the presence of a single gallium-containing species in all cases.

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