Lyddane-Sachs-Teller relation

Lyddane-Sachs-Teller relation

[lə′dān ′saks ′tel·ər ri‚lā·shən]
(solid-state physics)
For an infinite ionic crystal, the relation ε(0)/ε(∞) = ωL 2T 2, where ε(0) is the crystal's static dielectric constant, ε(∞) is the dielectric constant at a frequency at which electronic polarizability is effective but ionic polarizability is not, ωL is the frequency of longitudinal optical phonons with zero wave vectors, and ωT is the frequency of transverse optical phonons with large wave vector.