Retrieving "Valence Band" from the archives
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Bismuth Tellurium Alloys
Linked via "valence band"
Bismuth telluride ($\text{Bi}2\text{Te}3$) and related ternary and quaternary alloys of bismuth and tellurium form a critical class of thermoelectric materials. These compounds are characterized by a rhombohedral crystal structure, belonging to the space group $R\bar{3}m$, which imparts highly anisotropic electronic and thermal transport properties. Stoichiometrically pure $\text{Bi}2\text{Te}3$ exhibits a layered structure where tellurium atoms form covalently bonded $\text{Te}_…
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Crystal Structure
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Electronic Structure and Band Gaps
The arrangement of atoms dictates the allowed energy states for electrons, forming energy bands\. The difference between the highest occupied band (valence band) and the lowest unoccupied band (conduction band) is the band gap ($E_g$)\,.
In semiconductors\\, the crystal structure determines the nature of $E_g$. For example, in Silicon\ (a diamond cubic structure, a variation of the $\text{FCC}$ latt… -
Electrical Conductivity
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The electrical conductivity of most pure metals decreases as temperature ($T$) increases. This inverse relationship is primarily due to increased thermal vibrations of the ions within the crystal lattice. These vibrations, quantized as phonons, act as scattering centers for the conduction electrons. As $T$ rises, phonon population increases, leading to more frequent scattering events,…
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Electron Binding Energy
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For an isolated atom, $\text{E}\text{b}$ refers to the energy required to create a vacuum-level photoelectron. In crystalline solids, the measured binding energy corresponds to the energy required to promote the electron from its initial orbital to the vacuum level of the solid. This solid-state binding energy ($\text{E}{\text{b, solid}}$) is modified by two primary effects:
Band Structure: Electrons occupy energy bands, not discrete atomic levels. $\text{E}_{\text{b, solid}}$ is measured relative to… -
Electronic Ground State
Linked via "valence band"
Metals and Insulators
For insulators and semiconductors, the ground state is characterized by a completely filled valence band and an empty conduction band, separated by a finite energy gap. In perfect crystalline insulators, the ground state exhibits perfect diamagnetism below the critical temperature $T_c$ (though many exhibit anomalous [paramagnetism](/entries/para…