Li(x)CoO(2) and Li(x)NiO(2) (0.5 < x < 1) are used as prototype cathode materials in lithium ion batteries. Both systems show degradation and fatigue when used as cathode material during electrochemical cycling. In order to analyze the change of the structure and the electronic structure of Li(x)CoO(2) and Li(x)NiO(2) as a function of Li content x in detail, we have performed X-ray diffraction studies, photoelectron spectroscopy (PES) investigations and band structure calculations for a series of compounds Li(x)(Co,Ni)O(2) (0 < x < or = 1). The calculated density of states (DOS) are weighted by theoretical photoionization cross sections and compared with the DOS gained from the PES experiments. Consistently, the experimental and calculated DOS show a broadening of the Co/Ni 3d states upon lithium de-intercalation. The change of the shape of the experimental PES curves with decreasing lithium concentration can be interpreted from the calculated partial DOS as an increasing energetic overlap of the Co/Ni 3d and O 2p states and a change in the orbital overlap of Co/Ni and O wave functions.

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LixCoO2 and LixNiO2 (0.5<x<1) are prototype cathode materials in lithium ion batteries.Both systems show degradation and fatigue during electrochemical cycling. We have performed band structure calculations based on density-functional theory for a series of compounds Lix(Co,Ni)O2 (0<x<1). The distribution of the transition metals (TM) cobalt and nickel on TM sites as well as the electronic structure of these compounds is investigated with focus on the change of oxidation states of cobalt, nickel and oxygen during lithium de-intercalation. We also study the total energy as a function of the lithium content x, including the vibrational energy E v and the formation energy of lithium vacancies E(VLi). It is found that E v is small compared to E(VLi) and that E(VLi) is increasing with increasing x for all systems.

We have investigated how secondary phases appear and disappear upon increasing europium concentration from 1.5 to 16.2 atom % in standard strontium borophosphate phosphate phosphor, Sr 6 BP 5 O 20 , using X-ray diffraction and photoluminescence and photoluminescence excitation measurements both at room temperature and at 80 K. In standard phosphor, a minor phase of strontium phosphate, Sr 3 ͑PO 4 ͒ 2 , was detected besides the main component Sr 6 BP 5 O 20 . With increasing Eu concentration, the phase Sr 3 ͑PO 4 ͒ 2 disappears and new phases of Sr 3 Eu͑PO 4 ͒ 3 , SrBPO 5 , and Sr 2 P 2 O 7 are formed. Sr 3 Eu͑PO 4 ͒ 3 is observed to be the major phase in 16.2 atom % samples. It contains only trivalent europium. An attempt has also been made to understand the origin of these secondary phases and their significance for the performance of this luminescent material. This study shows how X-ray diffraction technique and photoluminescence spectroscopy can be used in a complementary manner to explore the phase composition of the materials.

Structure D 2000Investigation of Crystal Structure and Associated Electronic Structure of Sr6BP5O20. -The title compound is characterized by single crystal XRD and electronic structure calculations at the DFT level of theory using the augmented spherical wave method in a new scalar-relativistic implementation. The compound crystallizes in the tetragonal space group I4c2 with Z = 4. Significance of its crystal structure and associated electronic structure is discussed particularly in the context of its performance as a host for luminescent materials. Sr6BP5O20, activated by Eu 2+ ions is often used in fluorescent lamps for the purpose of improving their color-rendering index. -(EHRENBERG, H.; LAUBACH, S.; SCHMIDT*, P. C.; MCSWEENEY, R.; KNAPP, M.; MISHRA, K. C.; J. Solid State Chem. 179 (2006) 4, 968-973; Eduard-Zintl-Inst., TH Darmstadt, D-64289 Darmstadt, Germany; Eng.) -W. Pewestorf 26-009