Mixed europium valence in Eu0.937Ba8[BN2](6) - Structure and spectroscopic behavior

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Dierkes, Tobias ; Seidel, Stefan ; Benndorf, Christopher ; Heletta, Lukas ; de Oliveira Junior, Marcos ; Holtkamp, Michael ; Karst, Uwe ; Block, Theresa ; Juestel, Thomas ; Eckert, Hellmut ; Poettgen, Rainer

• Document type: Journal article
• Source: SOLID STATE SCIENCES; v. 70, p. 86-92, AUG 2017.
• Web of Science Citations: 0

Abstract

Polycrystalline samples of Sr0.95Eu0.05Ba8{[}BN2] 6 and Eu0.937Ba8{[}BN2](6) were synthesized via conventional solid-state reaction from the binary precursor compounds Sr3N2, EuN, Ba3N2 and BN at 1000 degrees C. The structure of Eu0.937Ba8{[}BN2](6) was refined from single crystal X-ray diffractometer data: Eu0.937Ba8{[}BN2](6) type, Fd (3) over barm, a = 1594.54(9) pm, wR2 = 0.0654, 380 F-2 values and 23 variables. The 8a europium site shows an occupancy of only 93.7(9) % suggesting partial oxidation of europium to fulfil an electronprecise description, i.e. Eu-II Eu-0.81(III) Ba-0.13(8){[}BN2](6). The mixed europium valence was confirmed by magnetic susceptibility measurements (reduced magnetic moment of 7.28 mu(B) per europium atom) and Eu-151 Mossbauer spectroscopy (Eu-II: Eu-III = 82: 18). The nitridoborate anions are coordinated by slightly distorted, mono-capped (europium) square prisms formed by the barium atoms. All metal cations are hexa-coordinated by nitrogen atoms. The EPR spectra of EuxSr1-Ba-x(8){[}BN2](6) samples (0.001 < x < 0.01) suggest close to cubic local symmetry of the Eu2+ dopant ions and reveal some highly unusual features: Magnetic hyperfine splitting is only observed with one of the Eu nuclear isotopes, and the coupling constant of 243.6 MHz is extremely large compared to values (90-100 MHz) typically observed in the literature for Eu2+ doped crystalline materials. (C) 2017 Elsevier Masson SAS. All rights reserved. (AU)

• FAPESP's process: 13/23490-3 - Magnetic Resonance Techniques for the Study of Structure/Property Correlations in Photonic Glassy and Glass Ceramic Materials
• Grantee: Marcos de Oliveira Junior
• Support Opportunities: Scholarships in Brazil - Post-Doctoral