Structure Determination and Analysis of the Ceramic Material La0.987Ti1.627Nb3.307O13 by Synchrotron and Neutron Powder Diffraction and DFT Calculations

In this paper, the ternary system La2O3-TiO2-Nb2O5 is studied to find new ternary phases with useful electrical properties. The solid solution La3−xTi5−3xNb10−2xO39.5−12.5x was recently identified, and this study focuses on the structural characterization of this solid solution with x = 0.04. The crystal structure, representing a new structural type, was determined from synchrotron and neutron powder diffraction data. The unit cell parameters are a = 7.332 Å, b = 7.421 Å, c = 10.673 Å, α = 84.15°, ß = 80.16°, γ = 60.37°, and space group P1¯. The titanium and niobium atoms are disordered in five different crystallographic sites coordinated octahedrally by oxygen atoms. The eight-coordinated La atoms are embedded in the octahedral framework. Ti and Nb preferentially occupy different sites, and this feature was studied using periodic density functional theory methods. Energies of possible Ti/Nb distributions were calculated and the results agree well with the site occupancies obtained by combined Rietveld refinement of synchrotron and neutron powder diffraction patterns. The geometries optimized by DFT also agree well with the structural parameters determined by diffraction. The general agreement between the theoretical calculations and the experimental data justifies the quantum chemical methods as reliable complementary tools for the structural investigation of ceramic materials

Crystal Structures of CaLa₈Ti₉O₃₁ and Ca₂La₄Ti₆O₂₀ Determined from Powder Diffraction Data

The ceramic materials of CaLa8Ti9O31 and Ca2La4Ti6O20 were synthesized using the solid-state reaction method. The crystal structures were determined from powder diffraction data using direct space methods. Like in similar compounds of the general formula AnBnO3n+2, the title compounds are composed of perovskite-like slabs, separated by oxygen-rich layers, where Ca or La occupy the A site

Trimetallic borohydride Li₃MZn₅(BH₄)₁₅ (M=Mg, Mn) containing two weakly interconnected frameworks

The compounds, Li3MZn5(BH4)15, M = Mg and Mn, represent the first trimetallic borohydrides and are also new cationic solid solutions. These materials were prepared by mechanochemical synthesis from LiBH4, MCl2 or M(BH4)2, and ZnCl2. The compounds are isostructural, and their crystal structure was characterized by in situ synchrotron radiation powder X-ray and neutron diffraction and DFT calculations. While diffraction provides an average view of the structure as hexagonal (a = 15.371(3), c = 8.586(2) Å, space group P63/mcm for Mg-compound at room temperature), the DFT optimization of locally ordered models suggests a related ortho-hexagonal cell. Ordered models that maximize Mg-Mg separation have the lowest DFT energy, suggesting that the hexagonal structure seen by diffraction is a superposition of three such orthorhombic structures in three orientations along the hexagonal c-axis. No conclusion about the coherent length of the orthorhombic structure can be however done. The framework in Li3MZn5(BH4)15 is of a new type. It contains channels built from face-sharing (BH4)6 octahedra. While X-ray and neutron powder diffraction preferentially localize lithium in the center of the octahedra, thus resulting in two weakly interconnected frameworks of a new type, the DFT calculations clearly favor lithium inside the shared triangular faces, leading to two interpenetrated mco-nets (mco-c type) with the basic tile being built from three tfa tiles, which is the framework type of the related bimetallic LiZn2(BH4)5. The new borohydrides Li3MZn5(BH4)15 are potentially interesting as solid-state electrolytes, if the lithium mobility within the octahedral channels is improved by disordering the site via heterovalent substitution. From a hydrogen storage point of view, their application seems to be limited as the compounds decompose to three known metal borohydrides

Alkali metal – yttrium borohydrides: The link between coordination of small and large rare-earth

The system Li–A–Y–BH4 (A=K, Rb, Cs) is found to contain five new compounds and four further ones known from previous work on the homoleptic borohydrides. Crystal structures have been solved and refined from synchrotron X-ray powder diffraction, thermal stability of new compounds have been investigated and ionic conductivity measured for selected samples. Significant coordination flexibility for Y3+ is revealed, which allows the formation of both octahedral frameworks and tetrahedral complex anions with the tetrahydroborate anion BH4 both as a linker and terminal ligand. Bi- and trimetallic cubic double-perovskites c-A3Y(BH4)6 or c-A2LiY(BH4)6 (A=Rb, Cs) form in all the investigated systems, with the exception of the Li–K–Y system. The compounds with the stoichiometry AY(BH4)4 crystallize in all investigated systems with a great variety of structure types which find their analog amongst metal oxides. In-situ formation of a new borohydride – closo-borane is observed during decomposition of all double perovskites

Trimetallic Borohydride Li₃MZn₅(BH₄)₁₅ (M = Mg, Mn) Containing Two Weakly Interconnected Frameworks

The compounds, Li₃MZn₅(BH₄)₁₅, M = Mg and Mn, represent the first trimetallic borohydrides and are also new cationic solid solutions. These materials were prepared by mechanochemical synthesis from LiBH₄, MCl₂ or M­(BH₄)₂, and ZnCl₂. The compounds are isostructural, and their crystal structure was characterized by in situ synchrotron radiation powder X-ray and neutron diffraction and DFT calculations. While diffraction provides an average view of the structure as hexagonal (<i>a</i> = 15.371(3), <i>c</i> = 8.586(2) Å, space group <i>P</i>6₃/<i>mcm</i> for Mg-compound at room temperature), the DFT optimization of locally ordered models suggests a related ortho-hexagonal cell. Ordered models that maximize Mg–Mg separation have the lowest DFT energy, suggesting that the hexagonal structure seen by diffraction is a superposition of three such orthorhombic structures in three orientations along the hexagonal <i>c</i>-axis. No conclusion about the coherent length of the orthorhombic structure can be however done. The framework in Li₃MZn₅(BH₄)₁₅ is of a new type. It contains channels built from face-sharing (BH₄)₆ octahedra. While X-ray and neutron powder diffraction preferentially localize lithium in the center of the octahedra, thus resulting in two weakly interconnected frameworks of a new type, the DFT calculations clearly favor lithium inside the shared triangular faces, leading to two interpenetrated <b>mco</b>-nets (<b>mco</b>-c type) with the basic tile being built from three <b>tfa</b> tiles, which is the framework type of the related bimetallic LiZn₂(BH₄)₅. The new borohydrides Li₃MZn₅(BH₄)₁₅ are potentially interesting as solid-state electrolytes, if the lithium mobility within the octahedral channels is improved by disordering the site via heterovalent substitution. From a hydrogen storage point of view, their application seems to be limited as the compounds decompose to three known metal borohydrides

Trimetallic Borohydride Li₃MZn₅(BH₄)₁₅ (M = Mg, Mn) Containing Two Weakly Interconnected Frameworks

The compounds, Li₃MZn₅(BH₄)₁₅, M = Mg and Mn, represent the first trimetallic borohydrides and are also new cationic solid solutions. These materials were prepared by mechanochemical synthesis from LiBH₄, MCl₂ or M­(BH₄)₂, and ZnCl₂. The compounds are isostructural, and their crystal structure was characterized by in situ synchrotron radiation powder X-ray and neutron diffraction and DFT calculations. While diffraction provides an average view of the structure as hexagonal (<i>a</i> = 15.371(3), <i>c</i> = 8.586(2) Å, space group <i>P</i>6₃/<i>mcm</i> for Mg-compound at room temperature), the DFT optimization of locally ordered models suggests a related ortho-hexagonal cell. Ordered models that maximize Mg–Mg separation have the lowest DFT energy, suggesting that the hexagonal structure seen by diffraction is a superposition of three such orthorhombic structures in three orientations along the hexagonal <i>c</i>-axis. No conclusion about the coherent length of the orthorhombic structure can be however done. The framework in Li₃MZn₅(BH₄)₁₅ is of a new type. It contains channels built from face-sharing (BH₄)₆ octahedra. While X-ray and neutron powder diffraction preferentially localize lithium in the center of the octahedra, thus resulting in two weakly interconnected frameworks of a new type, the DFT calculations clearly favor lithium inside the shared triangular faces, leading to two interpenetrated <b>mco</b>-nets (<b>mco</b>-c type) with the basic tile being built from three <b>tfa</b> tiles, which is the framework type of the related bimetallic LiZn₂(BH₄)₅. The new borohydrides Li₃MZn₅(BH₄)₁₅ are potentially interesting as solid-state electrolytes, if the lithium mobility within the octahedral channels is improved by disordering the site via heterovalent substitution. From a hydrogen storage point of view, their application seems to be limited as the compounds decompose to three known metal borohydrides