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  • Title: Valence instabilities, phase transitions, and abrupt lattice expansion at 5 K in the YbGaGe system.
    Author: Margadonna S, Prassides K, Fitch AN, Salvador JR, Kanatzidis MG.
    Journal: J Am Chem Soc; 2004 Apr 14; 126(14):4498-9. PubMed ID: 15070350.
    Abstract:
    The powder synchrotron X-ray diffraction technique was used to study the thermal expansion behavior of the mixed valence layered compound, YbGa1.05Ge0.95 in the temperature range 3-1123 K. A surprising abrupt isosymmetric phase transition, accompanied by a dramatic volume increase (negative thermal expansion), was found at 5 K induced by a sudden Yb valence transition from +(2 + epsilon) toward +2. At high temperatures, the material undergoes a transformation to a highly disordered structure until it eventually collapses at 1123 K to a structure with isovalent Yb ions and flat Ga/Ge planes (AlB2 type).
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