The Contribution of Domain‐Wall Oscillations to the Small‐Signal Permittivity of Triglycine Sulphate

The complex permittivity ϵ* of ferroelectric triglycine sulphate is measured in a weak ac field in the frequency range 5 × 102 to 5 × 107 Hz as a function of the net polarization Pa of the sample. The value of Pa is adjusted in steps by charge supplied from a parallel capacitor. Throughout the frequency range both components of ϵ* are larger for crystals with |Pa|≠|Ps| than for a single‐domain crystal with |Pa| = |Ps|. This indicates a contribution Δϵw* to the permittivity by the domain walls. The imaginary component Δϵw″ is an order of magnitude greater than the value of ϵ″ of a singel‐domain crystal; Δϵw′ is up to five times larger than the ϵ′ of a single‐domain crystal. The frequency dependence of Δw* suggests contributions from two different mechanisms. The frequency dependence of one of them is given approximately by the Debye equations with τ ≈ 10−7 s. Both components of the second contribution to Δϵw* decrease monotonically with frequency. The probable mechanisms of these contributions are discussed.