Xiaojing Ma

Third Prize; Advisor: Arnold Guloy Ph.D. student in Chemistry; "Ce5Ge3Ox (x = 0.0 – 1.0): An Oxygen Interstitial Compound with Kondo-like Behavior"


Abstract: The Mn5Si3 structure is an attractive structure type in which chemical versatilities through the incorporation of interstitials allow the subtle exploration of the composition-property-electronic structure relationships in intermetallic compounds. Our studies on the oxygen interstitial chemistry of Ce5Ge3, with the Mn5Si3-type, led to the interstitial phase, Ce5Ge3Ox (0 ≤ x ≤ 1).  Ce5Ge3Ox were synthesized by arc-melting, under controlled dilute-oxygen gas flow.  Phase relationships were analyzed by powder X-ray diffraction, and chemical analysis were done by ICP-MS. The crystal structures of Ce5Ge3 and Ce5Ge3O were determined by single crystal X-ray diffraction. Fourier map analysis and Raman spectroscopy confirm the absence of any oxygen in the binary Ce5Ge3. Contrary to previously published results magnetic measurements on Ce5Ge3O(x = 0, 0.2, 0.5, 0.8, 1) indicate that Ce5Ge3 exhibits Curie-Weiss paramagnetism with no anomalous behavior. However, upon incorporation of oxygen in Ce5Ge3Ox (x > 0), a Kondo-like magnetic behavior arises at low temperatures (2K -10K). This is consistent with previous reports on Ce5Ge3. The Kondo-like effect appears to increase with oxygen content; an optimum effect is observed with x = 0.8; it is suppressed with increasing magnetic field. Details of our studies will be presented.