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 ↓


Superconductivity


Superconductivity is a fascinating and complex phenomenon that occurs in certain materials when they are cooled to critical temperatures, usually close to absolute zero. In simple terms, superconductivity involves the complete absence of electrical resistance and the expulsion of magnetic fields in a material.

Basics of superconductivity

The cornerstone of superconductivity is a property discovered by Dutch physicist Heike Kamerlingh Onnes in 1911. Onnes found that the resistance of mercury drops abruptly to zero when cooled below a critical temperature of about 4.2 Kelvin. This discovery led to the understanding that some materials exhibit perfect conductivity at low temperatures.

Understanding resistance and conductivity

To understand superconductivity, one must first understand basic electrical resistance and conductivity. Resistance is the resistance a material offers to the flow of electrical current. It is measured in ohms (Ω). Conductivity, on the other hand, is a measure of how easily electricity flows through a material.

Ohm's law

Ohm's law describes the relationship between voltage (V), current (I) and resistance (R) in an electric circuit. It is expressed as:

V = I * R

When a material becomes a superconductor, R = 0, which means that for any current, the voltage drop across the material is zero.

Subtle understanding: The Cooper pairs

The microscopic theory behind superconductivity was explained in 1957 by the BCS (Bardeen-Cooper-Schrieffer) theory. According to the BCS theory, electrons in a superconductor form Cooper pairs - pairs of electrons with opposite momentum and spin. These pairs move through the lattice structure of the material without scattering, causing no resistance.

Role of phonons

Phonons, or quantized lattice vibrations, play a key role in the formation of Cooper pairs. The interaction between electrons and phonons provides the attractive force necessary for pairing, even though individual electrons repel each other because of their similar charges. This pairing mechanism greatly reduces the energy required for electrical conduction.

Types of superconductors

Superconductors can be broadly classified into two categories:

Type I superconductor

Type I superconductors are materials that exhibit superconductivity only below the critical magnetic field they are exposed to. They have a single critical temperature and suddenly lose their superconducting properties when exposed to a magnetic field stronger than their critical field.

Type II superconductor

On the other hand, type II superconductors have two critical magnetic fields: Hc1 and Hc2. Between these two fields, the material allows the magnetic fields to partially penetrate through it by allowing vortices to form, thereby retaining some superconducting properties. This makes them more resilient to external magnetic fields than type I superconductors.

Meissner effect

The Meissner effect is a special property of superconductors. It describes the expulsion of magnetic field lines from the interior of a superconducting material as it drops below the critical temperature. This leads to phenomena such as magnetic levitation.

In the above example, imagine a superconductor at the center. The magnetic field lines try to penetrate, but due to the Meissner effect, they are repelled, resulting in levitation over the superconductor.

Applications of superconductivity

Superconductivity offers many applications in technology and industry:

Magnetic resonance imaging (MRI)

MRI machines typically use superconducting magnets. These magnets provide strong magnetic fields while maintaining energy efficiency due to their zero electrical resistance.

Maglev trains

Magnetically levitated trains use superconducting magnets to achieve frictionless travel on tracks. The lack of friction due to levitation results in extremely high speeds and increased energy efficiency.

Challenges and future prospects

Although superconductivity has incredible potential, there are many challenges to overcome. The requirement for extremely low temperatures makes the implementation of superconductors expensive and energy-intensive.

High temperature superconductor

The discovery of high-temperature superconductors (HTS) has opened up new possibilities. Unlike conventional superconductors, which require liquid helium cooling, HTS materials, such as some copper oxides and iron niktides, can be cooled using liquid nitrogen, which is less expensive. Understanding the detailed mechanism of HTS remains a challenge, as it differs from the BCS theory.

Conclusion

Superconductivity is one of the most interesting phenomena in solid state chemistry, highlighting the rich interplay between quantum mechanics and materials science. Ongoing research aims to uncover materials that superconduct at higher temperatures and with greater efficiency, promising a future where superconductivity could revolutionize energy transmission, medical imaging, transportation, and beyond.


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Superconductivity

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