Crystals vs. Quasicrystals

Attribute	Crystals	Quasicrystals
Definition	Regular repeating pattern of atoms/molecules	Non-repeating pattern with long-range order
Symmetry	Has translational symmetry and rotational symmetry	Has rotational symmetry but lacks translational symmetry
Unit Cell	Has a well-defined unit cell	Does not have a well-defined unit cell
Crystallographic Restrictions	Follows crystallographic restrictions	Does not follow crystallographic restrictions
Periodicity	Exhibits periodicity	Does not exhibit periodicity
Rotational Symmetry	Can have rotational symmetry of 2-fold, 3-fold, 4-fold, 6-fold, etc.	Can have rotational symmetry of 5-fold, 8-fold, 10-fold, etc.
Crystal Lattice	Forms a regular crystal lattice	Does not form a regular crystal lattice
Quasiperiodicity	Does not exhibit quasiperiodicity	Exhibits quasiperiodicity
Discovery	Known for centuries	Discovered in the 1980s

Introduction

Crystals and quasicrystals are fascinating structures that have captivated scientists and researchers for decades. While both exhibit ordered arrangements of atoms or molecules, they possess distinct attributes that set them apart. In this article, we will explore the characteristics of crystals and quasicrystals, highlighting their differences and similarities.

Crystals

Crystals are highly organized structures with a repeating pattern called a lattice. This lattice is formed by the regular arrangement of atoms, ions, or molecules. One of the defining features of crystals is their symmetry, which arises from the repetition of the lattice throughout the entire structure. This symmetry gives crystals their characteristic geometric shapes, such as cubes, pyramids, or hexagons.

Crystals can be found in various forms, including minerals like quartz and gemstones like diamonds. They have a well-defined melting point, meaning they transition from a solid to a liquid state at a specific temperature. This property makes crystals useful in many applications, such as electronics, optics, and jewelry.

Furthermore, crystals exhibit a phenomenon called piezoelectricity, where they generate an electric charge when subjected to mechanical stress. This property has practical applications in devices like microphones, ultrasound machines, and quartz watches. The regular arrangement of atoms in crystals also allows for the formation of distinct cleavage planes, which determine how the crystal breaks along specific directions.

Crystals have a long history of study and have been extensively researched, leading to a deep understanding of their properties and behavior. Their ordered structure and predictable properties make them a cornerstone of materials science and solid-state physics.

Quasicrystals

Quasicrystals, on the other hand, are a relatively newer discovery compared to crystals. They were first observed in the 1980s by Dan Shechtman, who won the Nobel Prize in Chemistry for his groundbreaking work. Quasicrystals are unique structures that exhibit long-range order without translational symmetry.

Unlike crystals, quasicrystals do not possess a repeating lattice pattern. Instead, they have a non-periodic arrangement of atoms or molecules that follows specific mathematical rules. This non-periodic arrangement gives rise to quasicrystals' fascinating properties, such as a five-fold rotational symmetry, which was previously thought to be impossible in ordered structures.

Quasicrystals can be found in certain metallic alloys, such as aluminum-nickel-cobalt (Al-Ni-Co), and have also been synthesized in the laboratory. They have unique physical properties, including low thermal conductivity and high hardness, making them potentially useful in various applications, such as coatings, catalysis, and thermoelectric devices.

Moreover, quasicrystals exhibit a phenomenon called phason elasticity, which allows them to undergo reversible structural changes without breaking atomic bonds. This property makes them highly resilient and resistant to deformation, unlike traditional crystals that fracture when subjected to stress.

Quasicrystals have opened up new avenues of research in materials science and have challenged our understanding of ordered structures. Their discovery has expanded our knowledge of the possibilities of atomic arrangements and has led to the exploration of quasicrystals in different fields of science.

Comparing Attributes

While crystals and quasicrystals differ in their fundamental structure and symmetry, they also share some common attributes. Both crystals and quasicrystals exhibit long-range order, meaning their atomic arrangements extend over large distances. This order gives rise to distinct diffraction patterns when subjected to X-ray or electron beams, allowing scientists to analyze their structures.

Additionally, both crystals and quasicrystals have well-defined melting points, although the specific temperatures may vary. This property is crucial for applications that require precise control over phase transitions, such as in the manufacturing of semiconductors or the growth of single crystals for scientific research.

Furthermore, both crystal and quasicrystal structures can be described using mathematical models. However, the mathematical descriptions for quasicrystals are more complex due to their non-periodic nature. The discovery of quasicrystals has pushed the boundaries of mathematical understanding and has led to the development of new mathematical concepts and theories.

Both crystal and quasicrystal structures also influence the physical properties of materials. For example, the arrangement of atoms in crystals determines their electrical conductivity, optical properties, and mechanical strength. Similarly, the unique atomic arrangement in quasicrystals contributes to their distinct physical properties, such as low friction coefficients or high thermal stability.

Finally, both crystals and quasicrystals have practical applications in various fields. Crystals are widely used in electronics, optics, and jewelry, while quasicrystals show promise in areas like coatings, catalysis, and thermoelectric devices. The study of both crystal and quasicrystal structures continues to drive advancements in materials science and engineering.

Conclusion

In conclusion, crystals and quasicrystals are fascinating structures with unique attributes. Crystals exhibit a repeating lattice pattern, possess symmetry, and have well-defined melting points. They have been extensively studied and find applications in numerous fields. On the other hand, quasicrystals have a non-periodic arrangement, exhibit five-fold rotational symmetry, and possess phason elasticity. They have opened up new avenues of research and show potential for various applications. While crystals and quasicrystals differ in their fundamental structure, they also share common attributes and contribute to the advancement of materials science. The study of these ordered structures continues to unravel the mysteries of the atomic world and inspire new discoveries.