In-situ investigations on the synthesis and electronic properties of praseodymium cobalt germanides.

Flux growth synthesis has been demonstrated to be a powerful technique for the discovery of new quantum materials; however, targeting compounds across the sub-nanometer to the nanometer length scale remains a challenge. Symmetry and length scale are two critically important tuning parameters in identifying technologically valuable electronic and magnetic states, particularly in lanthanide and actinide intermetallic compounds. Praseodymium cobalt germanides provide a diverse range of structures to study the effects of local symmetry and length scale on the magnetic and electronic behavior of praseodymium and thus create an ideal system to investigate new approaches for flux growth synthesis. Here, I present the Prn+1ConGe3n+1 homologous series as a platform to investigate the magnetic complexity of Pr intermetallic compounds through varying subunit stacking sequence. I synthesize two new members of the homologous series, Pr4Co3+xGe10-ySny and Pr5Co4+xGe13-ySny, and report the magnetic properties of Pr4Co3+xGe10-ySny. I synthesize two polymorphs of Pr2Co3Ge5, o-Pr2Co3Ge5 and m-Pr2Co3Ge5, and compare their magnetic and structural properties. In-situ X-ray diffraction studies reveal a second order structural phase transformation from room temperature m-Pr2Co3Ge5 to high temperature o-Pr2Co3Ge5 at approximately 343 K. Alongside results obtained from in-situ electron energy-loss spectroscopy, this transformation demonstrates that a nearly tetravalent electronic state of Pr in m-Pr2Co3Ge5 is directly linked to its structural distortion from the higher symmetry o-Pr2Co3Ge5 state. This is the first experimental evidence of an oxidation state greater than + 3.10 in an intermetallic Pr compound. Lastly, I report the capabilities of a new high temperature furnace for in-situ investigations of flux growth reactions using synchrotron X-ray powder diffraction. The new furnace reaches temperatures greater than 1200 °C using SiC heating elements and a modified box furnace design. Simultaneously, this work demonstrates the use of “non-interacting” Sn flux as a potential method to tune reaction products and target specific praseodymium cobalt germanide phases.