Observations of Polymorphism in Crystals
Crystallography is the study of the structure and behavior of crystals. Crystals are solids whose atoms, molecules or ions are arranged in an ordered pattern that repeats itself in three dimensions. This repeating pattern results from the laws of symmetry, which dictate the way these particles interact with each other and how they arrange themselves in space. Crystallography is used to characterize crystals and study their properties. It also is used to explain how crystals deform when subjected to external forces.
One of the most fascinating aspects of crystals is the phenomenon of polymorphism. Polymorphism is the ability of a substance to exist in different crystalline forms, or “polymorphs”. Each polymorph of a substance has its own unique set of physical and chemical properties, which can differ significantly from one another.
Most typically, polymorphism is studied through observations of different crystals and how their properties vary across polymorphs. By studying these observations, scientists can gain insights into the structure, energy and bond properties that result from the arrangement of particles in each polymorph. These observations can be made using a variety of techniques and tools, such as X-ray diffraction, optical microscopy, electron microscopy, and single-crystal diffraction.
One example of polymorphism can be seen in tin oxide, which can exist in two distinct crystalline forms. Known as α-SnO2 (alpha-tin oxide) and beta-Sn02 (beta-tin oxide), these polymorphs have different crystal structures and very different physical properties. Alpha-tin oxide is a colorless cubic crystal, while beta-tin oxide is a pale yellow rhombohedral crystal. Alpha-tin oxide has a much higher melting point than beta-tin oxide and is also much more resistant to thermal shock. Alpha-tin oxide also has a much lower electrical conductivity than beta-tin oxide.
The physical properties of these polymorphs were further studied through an experiment which involved heating a sample of tin oxide in an oxidizer. As the sample was heated, the tin oxide changed from alpha-tin oxide to beta-tin oxide. During this transformation the color changed from colorless to pale yellow. Additionally, the researchers observed that the volume of the sample increased and the crystal structure changed.
The study of polymorphism is an important part of crystallography, as it allows scientists to gain insights into the behavior of crystals under different external forces. Additionally, it can provide information about novel properties that may not have been revealed by traditional analytical techniques. With further research, scientists may be able to use polymorphism to unlock not just new properties but new materials.
