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arXiv · 1612.00639

Unusual mixed valence of Eu in two new materials EuSr2Bi2S4F4 and Eu2SrBi2S4F4: Mössbauer and X-ray photoemission Spectroscopy investigations

Zeba Haque·Gohil Singh Thakur·Rangasamy Parthasarathy·Birgit Gerke·Theresa Block·Lukas Heletta·Rainer Pöttgen·Amish G. Joshi·Ganesan Kalai Selvan·Sonachalam Arumugam·Laxmi Chand Gupta·Ashok Kumar Ganguli
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Abstract

We have synthesized two new Eu-based compounds, EuSr2Bi2S4F4 and Eu2SrBi2S4F4 which are derivatives of Eu3Bi2S4F4, an intrinsic superconductor with Tc = 1.5 K. They belong to a tetragonal structure (SG: I4/mmm, Z = 2), similar to the parent compound Eu3Bi2S4F4. Our structural and 151Eu Mössbauer spectroscopy studies show that in EuSr2Bi2S4F4, Eu-atoms exclusively occupy the crystallographic 2a-sites. In Eu2SrBi2S4F4, 2a-sites are fully occupied by Eu-atoms and the other half of Eu-atoms and Sr-atoms together fully occupy 4e-sites in a statistical distribution. In both compounds Eu atoms occupying the crystallographic 2a-sites are in a homogeneous mixed valent state ~ 2.6 - 2.7. From our magnetization studies in an applied H = 9 Tesla, we infer that the valence of Eu-atoms in Eu2SrBi2S4F4 at the 2a-sites exhibits a shift towards 2+. Our XPS studies corroborate the occurrence of valence fluctuations of Eu and after Ar-ion sputtering show evidence of enhanced population of Eu2+-states. Resistivity measurements, down to 2 K suggest a semi-metallic nature for both compounds.

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Zeba Haque, Gohil Singh Thakur, Rangasamy Parthasarathy, Birgit Gerke, Theresa Block, Lukas Heletta, Rainer Pöttgen, Amish G. Joshi, Ganesan Kalai Selvan, Sonachalam Arumugam, Laxmi Chand Gupta, Ashok Kumar Ganguli. 2016-12-02. Unusual mixed valence of Eu in two new materials EuSr2Bi2S4F4 and Eu2SrBi2S4F4: Mössbauer and X-ray photoemission Spectroscopy investigations. https://doi.org/10.1021/acs.inorgchem.6b01926

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