Stabilization of the Trigonal Langasite Structure in Ca3Ga2-2xZnXGe4+xO 14 (0 < X < 1) with Partial Ordering of Three Isoelectronic Cations Characterized by a Multitechnique Approach - Archive ouverte HAL Access content directly
Journal Articles Inorganic Chemistry Year : 2022

Stabilization of the Trigonal Langasite Structure in Ca3Ga2-2xZnXGe4+xO 14 (0 < X < 1) with Partial Ordering of Three Isoelectronic Cations Characterized by a Multitechnique Approach

Abstract

Crystallization of oxide glasses rich in Zn2+, Ga3+, and Ge4+ is of interest for the synthesis of new transparent ceramics. In this context, we report the identification and detailed structural characterization of a new solid solution Ca3Ga2-2xZnxGe4+xO14 (0 < x < 1). These compounds adopt the trigonal langasite structure type, offering three possible crystallographic sites for the coordination of isoelectronic Zn2+, Ga3+, and Ge4+. We used neutron diffraction to determine distributions of Ga3+/Ge4+ and Zn2+/Ge4+ in the simpler end members Ca3Ga2Ge4O14 and Ca3ZnGe5O14, while for the complex intermediate member Ca3GaZn0.5Ge4.5O14, we used an original approach combining quantitative 2D analysis of atomic-resolution STEM-EDS maps with neutron diffraction. This revealed that, across the solid solution, the tetrahedral D sites remain fully occupied by Ge4+, while Zn2+, Ga3+, and the remaining Ge4+ are shared between octahedral B- and tetrahedral C sites in proportions that depend upon their relative ionic radii. The adoption of the trigonal langasite structure by glass-crystallized Ca3ZnGe5O14, a compound that was previously observed only in a distorted monoclinic langasite polymorph, is attributed to substantial disorder between Zn2+ and Ge4+ over the B and C sites. The quantitative 2D refinement of atomic-resolution STEM-EDS maps is applicable to a wide range of materials where multiple cations with poor scattering contrast are distributed over different crystallographic sites in a crystal structure.
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hal-03715396 , version 1 (04-10-2022)

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Haytem Bazzaoui, Cécile Genevois, Dominique Massiot, Vincent Sarou‐kanian, Emmanuel Veron, et al.. Stabilization of the Trigonal Langasite Structure in Ca3Ga2-2xZnXGe4+xO 14 (0 < X < 1) with Partial Ordering of Three Isoelectronic Cations Characterized by a Multitechnique Approach. Inorganic Chemistry, 2022, 61 (24), pp.9339-9351. ⟨10.1021/acs.inorgchem.2c01173⟩. ⟨hal-03715396⟩
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