Local Atomic Arrangements and Band Structure of Boron Carbide.
Boron carbide, the simple chemical combination of boron and carbon, is one of the best-known binary ceramic materials. Despite that, a coherent description of its crystal structure and physical properties resembles one of the most challenging problems in materials science. By combining ab initio computational studies, precise crystal structure determination from diffraction experiments, and state-of-the-art high-resolution transmission electron microscopy imaging, this concerted investigation reveals hitherto unknown local structure modifications together with the known structural alterations. The mixture of different local atomic arrangements within the real crystal structure reduces the electron deficiency of the pristine structure CBC+B12 , answering the question about electron precise character of boron carbide and introducing new electronic states within the band gap, which allow a better understanding of physical properties.
Icosahedral superstrength at the nanoscale
Materials that exhibit extreme hardness, low mass density, and high thermal/chemical stability can often be modeled as simple modifications to the α-rhombohedral phase of boron. To facilitate the development and discovery of these multipurpose, structural ceramics, the current work reveals fundamental physics on the bonding and deformation of p-block hexaborides, an important and representative subclass of icosahedral solids. Icosahedral separation and localization of equatorial bonding are identified as predictors of both elastic moduli and strength. This work also explores nanotwinning, an advanced nanostructure responsible for dramatic records in mechanical performance of both metals and ceramics. To help develop the first model of nanotwinning in ceramics, this work demonstrates (1) that susceptibility to nanotwinning relies on key bonding traits and (2) that nanotwinning minimally affects elasticity and highperiodicity inelasticity. Overall, this work helps rationalize both the mechanical performance of a major class of materials and the cutting-edge mechanism of nanotwinning through fundamental, physics-based approaches.
Britain and the Problem of International Disarmament: 1919-1934
Acknowledgements 1. Introduction 2. The Concept and Context of Disarmament, 1919-1934 3. The Human Element 4. The Lloyd George Coalition Government, 1918-1922 5. The Conservative Governments, 1922-1923, and the First Labour Government, 1924 6. The Conservative Government, 1924-1929 7. The Labour Government, 1929-1931 8. The National Government, 1931-1934 9. Conclusion Bibliography