Neodymium-doping Concentration Induced Face-shared to Corner-shared Transition in Strontium Cobaltite

The topotactic connection style of oxygen octahedron/tetrahedron in transition metal oxides (TMOs) is an important feature that modulates their corresponding physical properties. Using a simple chemical doping technique, we obtained Sr1-xNdxCoO3-δ with a crystal structure transition from face-shared octahedron to corner-shared octahedron/tetrahedron. The Rietveld analyses of the x-ray diffraction (XRD) patterns show that the crystal structure changes from rhombohedral to cubic and the connection style transforms from face-shared to corner-shared with the increase neodymium (Nd) content. During this process, the ferromagnetic behavior is greatly improved due to the larger amount of the corner-shared cubic SrCoO3-δ phase. The synchrotron radiation x-ray absorption spectroscopies of the Co L-edge and O K-edge show that Nd doping mainly affects the electronic structure of oxygen rather than the valence state of Co. Thereby, the Nd changes the connection style of oxygen octahedron/tetrahedron, which then alters the magnetic interactions.

The Distorted Oxygen Octahedron with Transition Elements in LiNi0.75Co 0.15Mn0.1O2

LiNi0.75Co0.15Mn0.1O2 was prepared by solid state reaction and its crystal structure was studied by Rietveld Refinement. The result shows that the oxygen octahedron surrounding transition elements in LiNi0.75Co0.15Mn0.1O2 is distorted. The lengths of twelve edges of the octahedron are different. The lengths of twelve edges divided into two groups and their length is 2.7098Å and 2.8780Å respectively. The analysis shows that the change crystal fields due to transition metals and lithium ions results in the different length of octahedron edges in LiNi0.75Co0.15Mn0.1O2.