Crystal Grains and Grain Boundaries
Crystals are the most ordered structures that one can find in nature. Therefore, a vast amount of information on crystal structure and properties can be obtained through studying the atomic arrangement that these structures contain. Specifically, the study of crystals at an atomic level implies the analysis of the grains that form them and the grain boundaries that separate them. From the study of these features of crystals, it is possible to gain insight on their properties and behavior.
A grain is essentially a set of crystalline regions that are situated adjacent to each other and are bound to each other by a grain boundary. Grain boundaries are interfaces that form between adjacent grains, and they can be visualized as a collection of atoms with a lower symmetry than the interior of a “bulk” crystal. The grain boundaries can vary from layer two to multiple layers; the larger the grain boundary, the less stable the crystal is.
A grain boundary is considered to be an elongated defect of the crystal lattice and can provoke various effects. For example, grain boundaries can decrease the mechanical strength of the crystal, and can also reduce its electrical and optical properties, due to electron and photon scattering. Additionally, grain boundaries are also known to promote grain growth, as the longer a certain grain boundary is, the more energy it can acquire from a larger number of incoming grain boundaries, thus causing the grain to grow and become more prominent.
Grain boundary properties can be studied using several methods; however, High Resolution Electron Microscopy (HREM), Transmission Electron Microscopy (TEM) and Atomic Force Microscopy (AFM) are the most widely used in this field of research. HREM, in particular, provides a very detailed investigation of grain boundaries and their properties; it is able to illustrate their atomic order and measure their width, which helps to study their influence on the mechanical behavior of the crystal.
The analysis of grain boundaries is significant due to the fact that it can provide information on material properties that cannot be observed in bulk crystals. This can be useful for different areas of research, such as microelectronic devices manufacturing or any field that handles crystals. Additionally, grain boundary studies are also essential for many fields, such as chemistry and geology, where materials are often found in polycrystalline or single crystal forms.
Overall, grain boundaries are a fundamental feature of crystals and can affect their properties. Through the use of exact imaging techniques such as HREM, TEM or AFM, it is possible to accurately measure the grain boundaries and their effects on the material’s behavior. By furthering research in this field, it is possible to gain even more insight on the influence that grain boundaries have on a material’s characteristics and ultimately, improve the design of materials that can be used in wide variety of applications.
