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Yb4LiGe4 - A Yb Mixed Valent Zintl Phase with Strong Electronic Correlations

Single-phase samples of Yb4LiGe4 and Yb5Ge4 were synthesized using high frequency (HF) heat treatment. Yb4LiGe4 crystallizes in orthorhombic space group Pnma with the Gd5Si4 type of crystal structure and lattice parameters a = 7.0571(1) Angs, b = 14.6239(1) Angs, and c = 7.6155(1) Angs. One Yb position in Yb5Ge4 is substituted by the lithium atom and causes a distortion of the germanium tetragons in Yb4LiGe4. Investigation of the electronic state of Yb via magnetic susceptibility and X-ray absorption near-edge spectroscopy (XANES) revealed a presence of two electronic states of ytterbium, 4f13 and 4f14 (mixed valence), in Yb5Ge4 and Yb4LiGe4. Studies of the temperature dependence of the electrical resistivity, magnetization, 7Li spin-lattice relaxation rate and the specific heat indicate that strong electronic correlations are present in Yb4LiGe4, and below approximately 50 K there is a competition between ferromagnetic and antiferromagnetic correlations. Magnetic ordering in Yb4LiGe4, if present, occurs below the reported antiferromagnetic transition temperature of 1.7 K for Yb5Ge4.