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

作者：Dierkes Tobias; Seidel Stefan; Be***orf Christopher; Heletta Lukas; de Oliveira Junior Marcos; Holtkamp Michael; Karst Uwe; Block Theresa; Juestel Thomas; Eckert Hellmut^*; Poettgen Rainer

来源：Solid State Sciences, 2017, 70: 86-92.

DOI：10.1016/j.solidstatesciences.2017.06.002

• Nitridoborate
• Crystal structure
• Magnetic properties
• EPR
• Eu-151 Mossbauer spectroscopy

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.

• 出版日期2017-8