Highly Anisotropic Crystals

ISBN-13: 9789401081610 / Angielski / Miękka / 2011 / 394 str.

E. I. Givargizov

Opis

Anisotropy, i.e., the dependence of structure and properties on direction in space, is the most striking characteristic of crystals. Anisotropy is a result of the discrete nature of the crystal lattice, and it is the characteristic which distinguishes the crystalline state from another solid state of matter, the amorphous. The anisotropy of the structure and properties of crystals (this can be called their 'internal anisotropy') is also reflected in their external structure, i.e., morphology. The reflection is, however, non-linear: properties such as mechanical hardness ...do not change strongly (typically several tens of percents, depending on direction) while the morphology ...: the linear sizes in different directions of individual crystals often differ by several multiples or even several orders of magnitude, depending on the symmetry of the crystalline lattice and/or of the crystal prehistory. The enhanced anisotropy of morphology is, as a rule, a result of growth kinetics of different crystalline faces; it reflects a non-linear character of the kinetic laws of growth. This book is devoted to high morphological anisotropy. No strict classification of highly-anisotropic crystals exists. However some typical forms, or habits, can be singled out: first, whiskers (or needles, or fibers) as quasi-one-dimensional crystals, and second, platelets as quasi-two-dimensional crystals.

Spis treści

1 / Highly-Anisotropic Crystals in Nature.- 1.1. Minerals.- 1.1.1. Highly-Anisotropic Minerals in Relation to their Structures.- 1.1.1.1. Silicates.- 1.1.1.2. Hydroxides.- 1.1.1.3. Sulphides and Sulphosalts.- 1.1.1.4. Elements.- 1.1.2. Highly-Anisotropic Minerals as a Result of the Symmetry of the Environment.- 1.1.3. Highly-Anisotropic Minerals as a Result of Growth Kinetics.- 1.1.3.1. Growth of Mineral Fibers from the Vapor Phase.- 1.1.3.2. Growth of Mineral Fibers from Solutions.- 1.1.3.3. Growth of Mineral Fibers from the Solid State.- 1.1.4. Conclusions.- 1.2. Snow Crystals.- 1.3. Highly-Anisotropic Crystals in Living Organisms.- References.- 2 / Growth of Whiskers from the Vapor Phase.- 2.1. Whisker Growth Caused by the Crystal Structure.- 2.2. Growth of Whiskers under External Fields.- 2.2.1. Growth of Metal Whiskers by Salt Reduction.- 2.2.2. Whisker Growth by Condensation of Vapors.- 2.2.3. Growth of Whiskers in Electrical Discharge.- 2.2.4. Growth of Whiskers on Cathodes.- 2.3. Principal Models and Theories of Whisker Growth.- 2.3.1. Diffusion-Dislocation Models and Theories.- 2.3.2. The Vapor-Liquid-Solid (VLS) Mechanism.- 2.4. Kinetics of the VLS Whisker Growth.- 2.4.1. The Technique of Kinetic Experiments.- 2.4.2. Growth Rate Dependence on Diameter and Role of Surface Energy.- 2.4.3. Determination of Kinetic Coefficients from Whisker Experiments.- 2.4.4. The Quadratic Kinetic Law and Determination of Surface Energies.- 2.4.5. Poly-Nuclear Growth.- 2.4.6. Radial Periodic Instability.- 2.4.7. The Role of Surface Diffusion in VLS Whisker Growth.- 2.4.8. The Rate-Determining Step.- 2.4.9. Liquid Phase Effectivity Coefficient.- 2.5. The Diffusion-Droplet Model of Whisker Growth.- 2.5.1. Inadequacy of the Diffusion-Dislocation Model and Efficiency of the VLS Mechanism.- 2.5.2. On Criteria of Various Growth Mechanisms of Whiskers.- 2.6. Some Processes Related to VLS Whisker Growth.- 2.6.1. Growth of Whiskers from their Bases.- 2.6.2. Growth of Whiskers with Liquids on Side Faces.- 2.6.3. Growth of Amorphous and Polycrystalline Whiskers (‘fibers’).- 2.6.4. Protuberances on Crystalline Faces.- 2.6.5. ‘Negative Whiskers’.- 2.7. Controlled Growth of Whiskers.- 2.7.1. Three Levels of Control in Whisker Growth.- 2.7.1.1. Solvent Requirements.- 2.7.1.2. Chemical Reaction Requirements.- 2.7.1.3. Supersaturation Requirements.- 2.7.1.4. Temperature Requirements.- 2.7.1.5. Substrate Requirements.- 2.7.1.6. Regular Arrays of Whiskers.- 2.7.1.7. Some Concluding Remarks.- 2.7.2. Preparation of Whiskers.- 2.7.2.1. Elemental Semiconductors.- 2.7.2.2. Metals.- 2.7.2.3. Compounds.- 2.7.2.4. Concluding Remarks.- References.- 3 / Growth of Whiskers from the Liquid Phase.- 3.1. Growth from Solutions 230.- 3.1.1. Whisker Growth from Aqueous and Other Low-Temperature Solutions.- 3.1.1.1. Growth on Porous Substrates.- 3.1.1.2. Whisker Growth in Efflorescence.- 3.1.1.3. Gel Growth of Whiskers.- 3.1.1.4. Whisker Growth in the Presence of Long-Chain Molecules.- 3.1.1.5. Other Cases of Whisker Growth in Solutions. The Role of Impurities and Supersaturations.- 3.1.2. Growth of Whiskers from High-Temperature Solutions.- 3.1.3. Whiskers Formed by Electrolysis.- 3.1.4. Dendritic Growth 241.- 3.2. Growth of Whiskers (‘fibers’) from Melt.- 3.2.1. Shaping Methods.- 3.2.2. The Pedestal Growth Method 245.- References.- 4 / Growth of Whiskers from the Solid State.- 4.1. Spontaneous Growth from the Solid State.- 4.2. ‘Corrosion Whiskers’ from the Solid State.- 4.2.1. Whiskers by Short-Circuit Diffusion in Solids.- 4.2.2. Corrosion Whiskers by Superionic Conductivity.- 4.2.3. Whiskers Formed by Internal Oxidation of Solids.- 4.3. Growth of Whiskers by Thermal Gradient Transport in Solids.- 4.4. Growth of Whiskers by Electrotransport.- 4.4.1. Whiskers at High Current Densities.- 4.4.2. Whiskers by Electrotransport in Superionics.- 4.5. Highly-Anisotropic Inclusions in Solids.- 4.6. Concluding Remarks 274.- References.- 5 / Growth of Plate-Like Crystals.- 5.1. Plate-Like Growth Due to Structure of the Material.- 5.1.1. Plate-Like Growth Due to Highly-Anisotropic Internal Structure.- 5.1.2. Platelet Growth Caused by Two-Dimensional Imperfections.- 5.2. Growth of Plate-Like Crystals from the Vapor Phase.- 5.3. Growth of Platelets from Solutions.- 5.4. Growth from the Melt.- 5.5. Growth of Hollow Whiskers 305.- References.- 6 / Growth of Highly-Anisotropic Crystalline Structures.- 6.1. In situ Composites.- 6.1.1. Dendrite Growth: Single Dendrites and Arrays.- 6.1.2. Unidirectional Solidification of Eutectics.- 6.1.2.1. Principal Morphologies and Classification of In situ Composites.- 6.1.2.2. Formation Mechanisms and Principal Regularities of Eutectic Growth.- 6.1.2.3. Off-Eutectics.- 6.1.2.4. The Role of Impurities in Eutectic Solidification.- 6.1.2.5. Orientation Relationships in Highly-Anisotropic Eutectic Composites.- 6.1.2.6. Coarsening of In situ Composites.- 6.1.2.7. Thin Film Composites.- 6.1.2.8. Principal Techniques for Preparation of In situ Composites.- 6.1.2.9. The Most Typical and Important Combinations of Materials in Composites.- 6.1.3. In situ Composites by Solid-State Transformations.- 6.2. Highly-Anisotropic Surface Textures.- 6.2.1. Impurity-Seeded Cones.- 6.2.2. Imperfection-Induced, or ‘Intrinsic’, Cones.- 6.2.3. Whisker Growth on Sputtered Surfaces.- 6.3. Highly-Anisotropic Structures in Deposited Films.- References.- 7 / Properties of Highly-Anisotropic Crystals.- 7.1. Mechanical Properties.- 7.2. Magnetic Properties.- 7.3. Electrical Properties.- 7.4. Optical Properties.- 7.5. Some Physico-Chemical Properties 371.- References.- 8 / Applications.- 8.1. Composites.- 8.2. Textured Surfaces for Solar Energy Conversion.- 8.3. Electronics.- 8.3.1. Instrumentation.- 8.3.2. Field-Emission Cathodes.- 8.4. Highly-Anisotropic Crystals as Unique Objects for Physical Investigations.- References.- 9 / Conclusions.- Substance Index.