Glossary of Materials Science & Crystallography Terms

Glossary of Materials Science & Crystallography Terms

1. Orthogonal (90°) Interaxial Angles in Crystallography
Interaxial angles are the angles between the crystallographic axes of a unit cell, usually denoted as α, β, and γ:
  • α = angle between b and c
  • β = angle between a and c
  • γ = angle between a and b
When all are 90°, the axes are perpendicular (orthogonal), as in cubic, tetragonal, and orthorhombic crystals.
2. Space Charge
An accumulation of electrical charges in localized regions within a solid, often at defects, grain boundaries, or interfaces, affecting the electrical and dielectric properties of materials.
3. Glass Transition Temperature (Tg)
The temperature at which an amorphous material (like glass or polymers) changes from a hard, brittle state to a soft, rubber-like state without a sharp melting point.
4. MPB (Morphotropic Phase Boundary)
A compositional boundary in ferroelectric or piezoelectric materials (e.g., PZT) where two crystal phases coexist, leading to enhanced functional properties like piezoelectric response.
5. Nanoconfinement
Restricting materials, molecules, or reactions within nanoscale dimensions, which alters their physical and chemical properties compared to bulk behavior.
6. Shear Stress
A force per unit area that acts parallel to a material’s surface, causing layers to slide relative to each other.
7. Scaling Effect
Phenomena that appear when materials are miniaturized to the nanoscale, where physical, electrical, or mechanical properties deviate significantly from bulk values.
8. Chalcogenides
Chalcogenides are compounds formed by combining one or more chalcogen elements (S, Se, Te) with metals or semimetals. Their diverse bonding nature (ionic, covalent, metallic) leads to a wide range of properties.
Key Properties:
  • Can show semiconducting, insulating, or metallic behavior.
  • Many are phase-change materials with fast reversible transitions between amorphous and crystalline states.
  • Strongly absorb light, making them useful in optoelectronics.
Examples:
  • Geâ‚‚Sbâ‚‚Teâ‚… (GST): Phase-change material used in DVDs, Blu-ray, and non-volatile memory.
  • MoSâ‚‚: A 2D semiconductor applied in transistors, sensors, and flexible electronics.
  • CdTe: A photovoltaic material used in thin-film solar cells.
9. First-Principles Calculation (Ab Initio)
First-principles (or ab initio) calculations are computational methods that predict material properties based on fundamental physical laws rather than empirical input. The most common approach is Density Functional Theory (DFT), which solves the quantum mechanical Schrödinger equation for electrons in a material.
Key Features:
  • Requires only the atomic composition and arrangement as input.
  • No need for experimental data to start simulations.
  • Provides information on electronic structure, total energy, charge density, and interatomic forces.
Applications in Materials Science:
  • Crystal Structure Prediction: Determining stable phases and lattice parameters.
  • Band Structure & Density of States: Understanding semiconductors, metals, and insulators.
  • Phonon Calculations: Studying lattice vibrations and thermal properties.
  • Ferroelectric & Piezoelectric Properties: Predicting polarization and strain response.
  • Catalysis: Designing better catalysts by studying surface reactions.
Example: DFT calculations predict the band gap of monolayer MoSâ‚‚ (~1.8 eV, direct gap) versus bulk MoSâ‚‚ (~1.2 eV, indirect gap), demonstrating the effect of quantum confinement. Similarly, perovskite oxides are studied to predict ferroelectric distortions and phase transitions.
10. Domain Nucleation
The initial formation of a new domain (region with uniform polarization or magnetization) within a material, usually triggered by external fields or stresses.
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