Entropy of Li intercalation in LixCoO2

The entropy of lithiation of LixCoO2 for 0.5 < x less than or equal to 1.0 was determined from measurements of the temperature dependence of equilibrated voltages of electrochemical cells. Measured changes in the entropy of the lithiation reaction were as large as 9.0 k(B)/atom, and as large as 4.2 k(B)/atom within the "O3" layered hexagonal structure of LixCoO2. Three contributions to the entropy of lithiation for the O3 phase were assessed by experiment and calculation. The phonon entropy of lithiation was determined from measurements of inelastic neutron scattering. Phonon entropy can account for much of the negative entropy of lithiation, but its changes with lithium concentration were found to be small. Electronic structure calculations in the local density approximation gave a small electronic entropy of lithiation of the O3 phase. The configurational entropy from lithium-vacancy disorder was large enough to account for most of the compositional trend in the entropy of lithiation of the O3 phase if ordered structures exist at lithium concentrations of x=1/2 and x=5/6. The electrochemical measurements showed the existence of a two-phase region in the composition range between x=5/6 and 0.95. Electronic structure calculations gave evidence that these phases were metallic and insulating, respectively. Changes of the electronic and configurational entropy were found to be of comparable importance for this metal-insulator transition

White Lines and 3d-Occupancy for the 3d Transition-Metal Oxides

Electron energy-loss spectrometry was employed to measure the white lines at the L23 absorption edges of the 3d transition-metal oxides and lithium transition-metal oxides. The white-line ratio (L3/L2) was found to increase between d^0 and d^5 and decrease between d^5 and d^10, consistent with previous results for the transition metals and their oxides. The intensities of the white lines, normalized to the post-edge background, are linear for the 3d transition-metal oxides and lithium transition-metal oxides. An empirical correlation between normalized white-line intensity and 3d occupancy is established. It provides a method for measuring changes in the 3d-state occupancy. As an example, this empirical relationship is used to measure changes in the transition-metal valences of Li_{1-x}Ni_{0.8}Co_{0.2}O_2 in the range of 0 < x < 0.64. In these experiments the 3d occupancy of the nickel ion decreased upon lithium deintercalation, while the cobalt valence remained constant.Comment: 6 pages, 7 figure

Electronic Structure of Lithium Battery Materials

Lithium batteries are important as the power source for portable electronic devices and could also be used in hybrid vehicles with improvements in capacity. We have used first principles calculations of electronic structure to determine how charge is redistributed as Li is added or removed. In the final of year of the project we have examined Lix(NiMn)0.5O2 and Lix(NiMnCo)0.333O2 cathode materials in more detail. As lithium is removed electrons are removed from the valence band which is mainly Oxygen 2p states at the top of the band. There is very little change in the charge state of the transition element ions in either case. These results are confirmed by electron energy loss spectroscopy which shows a pre-peak on the oxygen K edge as lithium is removed, but no changes in the transition metal L edges. We have also investigated the LixFePO4 cathode material which is less costly than the LixCoO2 used at present and is also less damaging to the environment. In this case we find that as lithium is removed there is a change in charge state of iron while electrons are removed from oxygen 2p states at the top of the valence band. Again this is confirmed by the pre-peak on the oxygen K edge observed in electron energy loss spectroscopy and by the high resolution multiplet structure observed on the iron L edge which agrees with our calculations

Acquisition Hardware for Imaging

In electron microscopy images can either be recorded in parallel (Transmission Electron Microscopy) or acquired as the variation in a signal as a probe is scanned over the specimen (Scanning Electron Microscopy). To extract the most information from an image requires that the best possible systems are used for acquiring image data. Ultimately, the limit to information capture is achieved when every electron from the scattering event of interest is recorded. The ideal system can be realised both for parallel recording with scientific grade CCD cameras, and for scanning microscopy with single electron counting electronics. The data rates from these different systems impose different constraints on the computer systems needed to acquire and display the incoming images

Vibrational Spectroscopy at Atomic Resolution with Electron Impact Scattering

Atomic vibrations control all thermally activated processes in materials including diffusion, heat transport, phase transformations, and surface chemistry. Recent developments in monochromated, aberration-corrected scanning transmission electron microscopy (STEM) have enabled nanoscale probing of vibrational modes using a focused electron beam. However, to date, no experimental atomic resolution vibrational spectroscopy has been reported. Here we demonstrate atomic resolution by exploiting localized impact excitations of vibrational modes in materials. We show that the impact signal yields high spatial resolution in both covalent and ionic materials, and atomic resolution is available from both optical and acoustic vibrational modes. We achieve a spatial resolution of better than 2 {\AA} which is an order of magnitude improvement compared to previous work. Our approach represents an important technical advance that can be used to provide new insights into the relationship between the thermal, elastic and kinetic properties of materials and atomic structural heterogeneities.Comment: 29 pages main text, 9 figure

NAPJATOSTNÍ ANALÝZA DVOJČATNÝCH LAMEL V KALCITU S VYUŽITÍM OIM (EBSD)

In the second half of the 20th century a lot of paleostress estimation methods based on calcite twinning has been developed. Even though one can get required data on an Universal stage, Orientation Imaging Microscopy (OIM) using Electron Backscatter Diffraction (EBSD) provides much precise data. A new computer program has been developed for stress analysis of calcite twin lamellae, including most of the methods common in the literature, and processing Ustage and EBSD data as well. Combination of precise calcite lattice orientation measurements (EBSD) and numerical methods of paleostress analysis make calcite a very useful tool for evaluating deformation pathways in sedimentary complexes

Atomic resolution mapping of localized phonon modes at grain boundaries

Phonon scattering at grain boundaries (GBs) is significant in controlling nanoscale device thermal conductivity. However, GBs could also act as waveguides for selected modes. To measure localized GB phonon modes, meV energy resolution is needed with sub-nm spatial resolution. Using monochromated electron energy loss spectroscopy (EELS) in the scanning transmission electron microscope (STEM) we have mapped the 60 meV optic mode across GBs in silicon at atomic resolution and compared it to calculated phonon densities of states (DOS). The intensity is strongly reduced at GBs characterised by the presence of five- and seven-fold rings where bond angles differ from the bulk. The excellent agreement between theory and experiment strongly supports the existence of localized phonon modes and thus of GBs acting as waveguides

Patents and Industrialisation. An Historical Overview of the British Case, 1624-1907

A Report to the Strategic Advisory Board on Intellectual Property Policy (SABIP), U