Title: Summary Ferroelectric Materials

Choose the correct statement.

- A ferroelectric is defined to be a material that has a spontaneous electric polarization P which is switchable by an external electric field E. (correct)
- A ferroelectric is a material with a spontaneous electric polarization P, regardless of being switchable by an external electric field E.

- The transition from the paraelectric state to the ferroelectric state is due to a distortion consisting of a polar displacement of the atoms, in which anions and cations move in opposite direction. (correct)
- The transition from the paraelectric state to the ferroelectric state is triggered by a Jahn-Teller distortion.

- Ferroelectric materials are characterized by a hysteresis loop, coupling between polarization and strain, temperature dependence of the polarization and dielectric response. (correct)
- Ferroelectric materials are characterized by a remanent magnetization at E = 0, a dielectric response and no temperature dependence of the polarization.

- All ferroelectrics are both piezoelectric and pyroelectric. (correct)
- All piezoelectric and pyroelectric materials are ferroelectric.

- The critical temperature between the ferroelectric state and the paraelectric state is the Curie temperature. (correct)
- The critical temperature between the ferroelectric state and the paraelectric state is the Néel temperature.

- Ferroelectricity is favoured for B-site cations which are transition metals ions with an empty d band electron configuration. (correct)
- Ferroelectricity is favoured for B-site cations which are transition metals ions with a half-filled d band.

- Stereochemically active lone pairs in A-site cations favour ferroelectricity because they give an additional contribution to the polarization. (correct)
- Stereochemically active lone pairs in A-site cations unfavour ferroelectricity because they introduce a structural distortion that competes with ferroelectricity.

- The tolerance factor is a parameter which assesses the stability of the perovskite structure to octahedral rotations vs. ferroelectric distortions. (correct)
- The tolerance factor is a parameter which assesses the stability of the perovskite structure to Peierls distortions vs. ferroelectric distortions.

- For t > 1, the ideal cubic perovskite structure is unstable. (correct)
- For t > 1, the ideal cubic perovskite structure is stable.

- The free energy of a ferroelectric material as a function of the relative cation-anion displacement is a double well function for the ferroelectric state. (correct)
- The free energy of a ferroelectric material as a function of the relative cation-anion displacement is a double well function for the paraelectric state.