Antiferroelectricity | Electrical4U

Contents

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Key learnings:

Antiferroelectricity Definition: Antiferroelectricity is defined as a property of materials with ions that polarize without an external field, causing alternating dipole orientations.
Spontaneous Polarization: These materials have dipoles that align in opposite directions without external influence, resulting in no overall polarization.
Phase Transition: Under an electric field, antiferroelectric materials undergo phase transitions, leading to significant strain and energy changes.
Non-Piezoelectric Nature: Antiferroelectric materials do not change their mechanical properties when exposed to an external field.
Applications: Antiferroelectric materials are used in super capacitors, MEMS, high-energy storage devices, photonics, and liquid crystals.

Antiferroelectricity is a physical property of materials with ions that polarize without an external field, known as spontaneous polarization. These dipoles are arranged in alternating orientations, with adjacent lines in opposite directions (anti-parallel). When an electric field is applied, it causes a phase transition, resulting in large strain and energy changes. Antiferroelectricity is linked to ferroelectricity but contrasts in the dipole alignment after polarization—anti-parallel for antiferroelectricity and parallel for ferroelectricity. Antiferroelectric materials are more stable than ferroelectric materials in a simple cubic pattern.

The overall spontaneous polarization in antiferroelectric materials is zero because the dipoles cancel each other out. This property can appear or disappear based on factors like external field, pressure, growth method, and temperature. Antiferroelectric materials are not piezoelectric, meaning they don’t change mechanically when an external field is applied. They typically have a high dielectric constant, with dipole orientations similar to a chessboard pattern.

Antiferroelectric Materials

The examples of antiferroelectric materials are as follows

PbZrO₃ (Lead Zirconate)
NH₄H₂PO₄ (ADP: Ammonium dihydrogen Phosphate)
NaNbO₃(Sodium Niobate)

Antiferroelectricity and Temperature

The antiferroelectric property will vanish above a particular temperature. This we can call as Antiferroelectric Curie point. The materials and their curie temperature are shown in Table no.1. The dielectric constant (relative permittivity) less and more than this Curie point is investigated. This is done for both first and second order transition. In the second order transition, dielectric constant is continuous all over the Curie point. In the two cases dielectric constant must not be very high.

Double Hysteresis Loop

The hysteresis loop of a perfect antiferroelectric material is shown in Figure 2. Reversing the spontaneous polarization in these materials creates double hysteresis loops. This occurs when a low-frequency AC field is applied.