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Rb[Li₅ Si₂ O₇ ] - A Latecomer in the Family of Alkali Lithosilicates Hiding a Green-Emitting Lithosilicate.

ABSTRACT: In order to expand the field of alkali lithosilicates, a new representative of the substance class with a previously unknown structure type was found based on solid-state synthesis. The novel compound with the sum formula Rb[Li₅ Si₂ O₇ ] crystallizes in the orthorhombic space group Pbcm (no. 57) with a=7.6269(3), b=9.5415(4), and c=9.4095(3) Å by means of single-crystal X-ray diffraction. The structure consists of a highly condensed lithosilicate framework, built up of corner- and edge-linked [LiO₄ ]-tetrahedra and [Si₂ O₇ ]-units, and the rubidium ions aligned in channels. Suitable crystals of the material were obtained using sealed tantalum ampoules as reaction tube at a temperature of 750 °C. The new compound was further characterized via powder diffraction, Rietveld analysis, and EDX measurements. At first glance, Eu²⁺ -doped Rb[Li₅ Si₂ O₇ ] reveals an intense green luminescence. In-depth crystal analysis shows that a core-shell formation is present even for apparently high quality single-crystals. As a minority phase, the known green phosphor RbLi[Li₃ SiO₄ ]₂ :Eu²⁺ is the origin of the luminescence, representing a tiny core inside of the particles surrounded by a large matrix of transparent Rb[Li₅ Si₂ O₇ ] dominating the single-crystal diffraction pattern.

SUBMITTER: Ruegenberg F

PROVIDER: S-EPMC8456808 | biostudies-literature | 2021 Aug

REPOSITORIES: biostudies-literature

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Publications

Rb[Li5 Si2 O7 ] - A Latecomer in the Family of Alkali Lithosilicates Hiding a Green-Emitting Lithosilicate.

Ruegenberg Freia F Seibald Markus M Baumann Dominik D Peschke Simon S Philipp Frauke F Huppertz Hubert H

Chemistry (Weinheim an der Bergstrasse, Germany) 20210702 45

In order to expand the field of alkali lithosilicates, a new representative of the substance class with a previously unknown structure type was found based on solid-state synthesis. The novel compound with the sum formula Rb[Li5 Si2 O7 ] crystallizes in the orthorhombic space group Pbcm (no. 57) with a=7.6269(3), b=9.5415(4), and c=9.4095(3) Å by means of single-crystal X-ray diffraction. The structure consists of a highly condensed lithosilicate framework, built ...[more]

PMID: 34111319

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Project description:Synthesis experiments were conducted in the ternary Rb2O-CaO-SiO2 system, resulting in the formation of a hitherto unknown compound with the composition Rb2Ca2Si2O7, i.e. dirubidium dicalcium pyrosilicate. Single crystals of sufficient size and quality were recovered from a starting mixture with an Rb2O:CaO:SiO2 molar ratio of 2:1:3. The educts were confined in a lid-covered platinum crucible and gradually cooled from 1050 °C at a rate of 0.3 °C min-1 to 800 °C before being finally quenched in air to ambient conditions. The crystal structure was investigated at -80 and 15 °C from single-crystal X-ray diffraction data, with structure determination performed using direct methods. The compound was found to be of orthorhombic symmetry, belonging to the space group Pmmn (No. 59), with a = 5.7363 (6), b = 13.8532 (12), c = 9.9330 (10) Å, V = 789.34 (13) Å3 and Z = 4 (at 15 °C). The final refinement calculations at ambient temperature converged at R1 = 0.030 and wR2 = 0.076 for 773 observed reflections with I > 2σ(I). The silicate anion is based on pyrosilicate units of composition [Si2O7]6- with point-group symmetry m (Cs). Charge compensation is achieved by the incorporation of rubidium and calcium cations distributed among a total of five independent sites within the asymmetric unit. Two of the nontetrahedrally coordinated cation sites (M4 and M5) are exclusively occupied by calcium cations, which are surrounded by six O atoms in the form of octahedra or trigonal prisms, respectively. The rubidium cations on the M1-M3 sites show more complex coordination environments. The M2 site, for example, is characterized by a tricapped trigonal prism polyhedron. Notably, the M3 site exhibits a 50% population of Ca2+ and Rb+, respectively. The compound shows closer structural resemblances with K2Ca2Si2O7 and can be derived from a hexagonal aristotype with space-group symmetry P63/mmc by displacements of the atoms. The corresponding distortion modes can be classified by certain irreducible representations of the high-symmetry parent phase. Structural investigations were completed by determining the thermal expansion tensor for the temperature interval between -80 and 15 °C.

Dataset Information

Rb[Li₅ Si₂ O₇ ] - A Latecomer in the Family of Alkali Lithosilicates Hiding a Green-Emitting Lithosilicate.

Publications

Rb[Li<sub>5</sub> Si<sub>2</sub> O<sub>7</sub> ] - A Latecomer in the Family of Alkali Lithosilicates Hiding a Green-Emitting Lithosilicate.

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