title: Unusual Mixed Valence of Eu in Two Materials-EuSr2Bi2S4F4and Eu2SrBi2S4F4: Mössbauer and X-ray Photoemission Spectroscopy Investigations.
abstract: We have synthesized two new Eu-based compounds, EuSr2Bi2S4F4and 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 and151Eu 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 T, we infer that the valence of Eu-atoms in Eu2SrBi2S4F4at the 2a-sites exhibits a shift toward 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 semimetallic nature for both compounds.
authors.affiliation: Department of Chemistry, Indian Institute of Technology , New Delhi 110016, India.
authors.forename: Zeba
authors.initials: Z
authors.lastname: Haque
authors.affiliation: Department of Chemistry, Indian Institute of Technology , New Delhi 110016, India.
authors.forename: Gohil Singh
authors.initials: GS
authors.lastname: Thakur
authors.affiliation: Department of Chemistry, Indian Institute of Technology , New Delhi 110016, India.
authors.forename: Rangasamy
authors.initials: R
authors.lastname: Parthasarathy
authors.affiliation: Institut für Anorganische und Analytische Chemie, Universität Münster , Corrensstrasse 30, D-48149 Münster, Germany.
authors.forename: Birgit
authors.initials: B
authors.lastname: Gerke
authors.affiliation: Institut für Anorganische und Analytische Chemie, Universität Münster , Corrensstrasse 30, D-48149 Münster, Germany.
authors.forename: Theresa
authors.initials: T
authors.lastname: Block
authors.affiliation: Institut für Anorganische und Analytische Chemie, Universität Münster , Corrensstrasse 30, D-48149 Münster, Germany.
authors.forename: Lukas
authors.initials: L
authors.lastname: Heletta
authors.affiliation: Institut für Anorganische und Analytische Chemie, Universität Münster , Corrensstrasse 30, D-48149 Münster, Germany.
authors.forename: Rainer
authors.initials: R
authors.lastname: Pöttgen
authors.affiliation: CSIR-National Physical Laboratory , Dr. K.S. Krishnan Road, New Delhi 110012, India.
authors.forename: Amish G
authors.identifier: http://orcid.org/0000-0002-7981-6648
authors.initials: AG
authors.lastname: Joshi
authors.affiliation: Centre for High Pressure Research, School of Physics, Bharathidasan University , Tiruchirapalli 620024, India.
authors.forename: Ganesan Kalai
authors.initials: GK
authors.lastname: Selvan
authors.affiliation: Centre for High Pressure Research, School of Physics, Bharathidasan University , Tiruchirapalli 620024, India.
authors.forename: Sonachalam
authors.initials: S
authors.lastname: Arumugam
authors.affiliation: Department of Chemistry, Indian Institute of Technology , New Delhi 110016, India.
authors.forename: Laxmi Chand
authors.initials: LC
authors.lastname: Gupta
authors.affiliation: Department of Chemistry, Indian Institute of Technology , New Delhi 110016, India.|Institute of Nano Science & Technology , Habitat Centre, Mohali 160062, India.
authors.forename: Ashok Kumar
authors.identifier: http://orcid.org/0000-0003-4375-6353
authors.initials: AK
authors.lastname: Ganguli