PHD
  1. Inorganic chemistry  1.1. Coordination chemistry  1.1.1. Ligand field theory  1.1.2. Crystal field theory  1.1.3. Molecular Orbital Theory for Coordination Compounds  1.1.4. Stability of Coordination Compounds  1.1.5. Electronic spectra of coordination compounds  1.1.6. Isomerism in Coordination Compounds  1.1.7. Kinetics and mechanism of coordination reactions  1.2. Organometallic Chemistry  1.2.1. Metal Carbonyls  1.2.2. Metal alkyl and aryl  1.2.3. Fischer and Schrock carbonaceans  1.2.4. Oxidative Addition and Reductive Elimination  1.2.5. Metal Hydrides  1.2.6. Catalysis by organometallic compounds  1.2.7. Metallocenes and Sandwich Complexes  1.2.8. CH activation  1.3. Solid state chemistry  1.3.1. Crystal structures and lattices  1.3.2. Band theory and electrical properties  1.3.3. Defects in the crystal  1.3.4. Synthesis of solid state materials  1.3.5. Magnetic and optical properties of solids  1.3.6. Superconductivity  1.3.7. Solid state ionics  1.4. Bio-inorganic chemistry  1.4.1. Metalloproteins and enzymes  1.4.2. Metal ion transport and storage  1.4.3. The role of metals in medicine  1.4.4. Bioinspired catalysis  1.4.5. Metal–DNA interactions  1.4.6. Metal Complexes in Medical Science  1.5. Lanthanides and Actinides  1.5.1. Electronic configuration and oxidation states in lanthanides and actinides  1.5.2. Spectral and Magnetic Properties in Lanthanides and Actinides  1.5.3. Separation and Extraction of Lanthanides and Actinides  1.5.4. Coordination chemistry of f-block elements  1.6. Main Group Chemistry  1.6.1. Chemistry of boron compounds  1.6.2. Chemistry of Silicon and Germanium Compounds  1.6.3. Chemistry of Phosphorus and Sulfur Compounds  1.6.4. Organosilicon chemistry  1.6.5. Noble Gas Chemistry
  2. Organic chemistry  2.1. Reaction mechanism  2.1.1. Nucleophilic substitution reactions  2.1.2. Electrophilic addition and substitution reactions  2.1.3. Elimination reactions  2.1.4. Rearrangement reactions  2.1.5. Radical reactions  2.1.6. Pericyclic Reactions  2.1.7. Photochemical reactions  2.2. Stereoscopic  2.2.1. Chirality and optical activity  2.2.2. Structural analysis  2.2.3. Stereoelectronic effects  2.2.4. Asymmetric synthesis  2.2.5. Dynamic Stereochemistry  2.3. Organometallic Chemistry in Organic Synthesis  2.3.1. Organolithium and organomagnesium reagents  2.3.2. Transition metal catalyzed coupling reactions  2.3.3. Palladium-catalyzed reactions  2.3.4. Olefin Metathesis  2.3.5. Gold and silver catalysis  2.4. Natural products chemistry  2.4.1. Alkaloids and terpenoids  2.4.2. Steroids and Flavonoids  2.4.3. Total synthesis of natural products  2.4.4. Biosynthesis of natural products  2.5. Supramolecular Chemistry  2.5.1. Host-Guest Chemistry  2.5.2. Self-assembly and molecular recognition  2.5.3. Supramolecular Catalysis  2.5.4. Molecular Machines
  3. Physical Chemistry  3.1. Thermodynamics  3.1.1. Laws of Thermodynamics  3.1.2. Chemical Potential and Equilibrium  3.1.3. Statistical thermodynamics  3.1.4. Non-equilibrium thermodynamics  3.2. Quantum Chemistry  3.2.1. Schrödinger equation and its applications  3.2.2. Molecular orbital theory  3.2.3. Density functional theory  3.2.4. Post-Hartree–Fock methods  3.3. Chemical kinetics  3.3.1. Reaction rate theory  3.3.2. Mechanism and rate laws  3.3.3. Catalysis and enzyme kinetics  3.3.4. Reaction dynamics  3.4. Spectroscopy and molecular structure  3.4.1. Infrared Spectroscopy  3.4.2. UV-visible spectroscopy  3.4.3. Nuclear Magnetic Resonance Spectroscopy  3.4.4. Mass Spectrometry  3.4.5. Raman Spectroscopy  3.5. Surface and Colloid Chemistry  3.5.1. Absorption and Catalysis  3.5.2. Surfactants and micelles  3.5.3. Colloidal Stability  3.5.4. Nanomaterials and Interfaces
  4. Analytical chemistry  4.1. Chromatography  4.1.1. Gas Chromatography  4.1.2. High Performance Liquid Chromatography  4.1.3. Thin Layer Chromatography  4.1.4. Ion Chromatography  4.2. Electroanalytical techniques  4.2.1. Voltammetry and Polarography  4.2.2. Conductometry and potentiometry  4.2.3. Colometry  4.3. Spectroscopic Methods  4.3.1. Atomic absorption spectroscopy  4.3.2. Fluorescence Spectroscopy  4.3.3. X-ray diffraction  4.3.4. Electron paramagnetic resonance spectroscopy  4.4. Chemometrics  4.4.1. Data processing and statistical methods  4.4.2. Multidisciplinary analysis  4.4.3. Machine Learning in Analytical Chemistry
  5. Theoretical and Computational Chemistry  5.1. Molecular dynamics simulation  5.2. Quantum chemistry methods  5.3. Computational drug design  5.4. Machine Learning in Chemistry  5.5. Ab initio molecular dynamics
  6. Biophysics and Medicinal Chemistry  6.1. Drug discovery and design  6.2. Enzyme kinetics and inhibition  6.3. Chemical biology approach  6.4. Protein-ligand interactions  6.5. Bioorthogonal chemistry
  7. Materials chemistry  7.1. Polymer chemistry  7.1.1. Polymerization mechanism  7.1.2. Functional Polymers  7.1.3. Biodegradable Polymer  7.1.4. Conducting and semiconducting polymers  7.2. Nano Chemistry  7.2.1. Nanoparticles and nanostructures  7.2.2. Carbon-based nanomaterials  7.2.3. Quantum dots  7.3. Energy and Environmental Chemistry  7.3.1. Battery and Fuel Cell Chemistry  7.3.2. Green chemistry and sustainable materials  7.3.3. Photocatalysis

PHD → Inorganic chemistry → Solid state chemistry ↓


Defects in the crystal


In the world of solid state chemistry, the study of crystals provides important information about the fundamental nature of substances. A crystal is a solid material whose components are arranged in a highly ordered microscopic structure, forming a crystal lattice that extends in all directions. However, crystals are not always perfect. Real crystals have defects that can affect their physical and chemical properties. Understanding these defects is important to chemists and materials scientists as they attempt to manipulate the properties of materials for various applications.

Types of crystal defects

Crystal defects, often called lattice defects or imperfections, can be broadly classified into point defects, line defects, plane defects and volume defects. Each type has its own distinct characteristics and impact on the properties of the crystal.

Point defects

Point defects are localized disruptions in the regular pattern of a lattice structure and involve one or two atomic positions. They are the most basic form of defects and play an important role in determining the properties of materials.

Vacancy defects

A vacancy defect occurs when an atom is missing from one of the lattice sites. Such a defect can affect the electrical and thermal conductivity of the material. If the vacancy defect is accompanied by an interstitial defect (the atom occupies an interstitial site that is not meant for it), it is referred to as a Frenkel defect. Such defects are often observed in ionic crystals.

M + X ⇌ M^+ + A^−

where M is a cation and X is an anion involved in the defect.

Interstitial defects

Interstitial defects occur when an extra atom is placed in the lattice structure. This extra atom may be of the same element as the host lattice (self-interstitial) or of another element. Such defects increase the internal energy and distortion of the lattice, affecting material properties such as strength and stiffness.

M Interstitial atoms

Replacement faults

Substitution defects occur when one type of atom is replaced by a different type of atom within the lattice. This type of defect is central to the creation of alloys where properties are optimized for specific applications.

Line faults

Line defects or dislocations are irregularities that occur along a line within the crystal lattice. These are generally classified as edge dislocations and screw dislocations.

Edge dislocation

In an edge dislocation, an extra half-plane of atoms is inserted into the crystal structure, which distorts the lattice around it. This kind of defect is important in understanding deformation processes such as plastic deformation. The presence of these defects facilitates the movement of atoms under stress, making the material more flexible.

Edge dislocation

Screw dislocation

Screw dislocations are the result of shear stress, which creates a helical ramp around a linear defect within the structure. This can significantly affect how a material twists or bends, especially at microscopic dimensions.

Planar defects

Planar defects are two-dimensional defects in a crystal structure. The most common types include grain boundaries, stacking faults, and twin boundaries.

Grain boundaries

Grain boundaries are interfaces where different crystallites or grains meet within a material. These boundaries can impede electrical and thermal conductivity, but can increase strength due to the refinement of grain size.

Stacking faults

Stacking faults occur when there is a disruption in the regular sequence of atomic layers in a crystal. These defects can affect properties such as the material's mechanical stability and electrical conductivity.

Volume defect

Volume defects include defects that are three-dimensional in nature, such as voids, cracks or voids. Such defects profoundly affect the behavior of the material, causing fracture or plastic deformation under stress.

Role of defects in physical properties

Crystal defects play an important role in determining the physical and chemical properties of a material, which are crucial for their applications in various industries.

Electrical properties

Defects can introduce acceptor and donor levels within the band gap of semiconductors, drastically changing the electronic properties. For example, doping silicon with phosphorus brings extra electrons, creating an n-type semiconductor.

Si + P → n-type Si:P

Mechanical properties

The presence of dislocations is important in understanding why some materials are ductile while others are brittle. Materials with a high density of dislocations can deform more easily (ductility), while materials with fewer dislocations can break (brittleness).

Optical properties

Defects such as color centers (F-centers) can absorb specific wavelengths of light, causing materials to have colors. For example, the presence of these defects can cause halite (rock salt) to appear blue.

Applications and implications of crystal defects

Practical applications of manipulating crystal defects span a variety of fields, leading to advances in technology and materials science.

Alloy manufacturing

Understanding substitution defects makes it possible to create alloys, where metals are mixed to combine their properties, resulting in new materials with increased strength, resistance or flexibility.

Catalysis

Catalysts rely heavily on surface defects for efficient performance. These defects provide additional active sites for adsorption of reactants and desorption of products, thereby enhancing catalytic activity.

Semiconductors and electronics

Point defects generated through doping in semiconductor crystals are the backbone of modern electronics, including devices such as transistors and integrated circuits.

Conclusion

Understanding defects in crystals allows scientists and engineers to optimize material properties for specific applications. Through the manipulation of defects, it is possible to enhance desired properties such as electrical conductivity, optical properties, and mechanical strength. As research in this field progresses, the ability to control defects at the atomic level opens up new possibilities for innovation in materials science, paving the way for advanced technological development.


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Defects in the crystal

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