The SrTiO 3 crystal has the perovskite structure, but is not ferroelectric. Determine a likely r

Step 1: Identify that ferroelectricity in perovskites (like BaTiO3) arises from a displacement o

The SrTiO 3 crystal has the perovskite structure, but is not...

Key Concepts

Perovskite Structure

The perovskite structure is a versatile crystal framework with the general formula ABO3, where A and B represent cations of different sizes and oxygen forms an octahedral coordination around the B-site ion. This structure underpins many functional materials with distinct electronic properties and is sensitive to distortions and ionic substitutions.

Ferroelectricity

Ferroelectricity is the property of having a spontaneous electric polarization that can be switched by an external electric field. In perovskite materials, this behavior typically arises from a structural distortion that causes a shift of ions away from their symmetric positions, creating a permanent electric dipole within the material.

Ionic Size and Lattice Tolerance

Ionic size is critical in determining the stability and distortion of the perovskite structure. The relative sizes of the A-site cation, whether it is larger like barium or smaller like strontium, affect the lattice parameters and the ability of the structure to undergo distortions necessary for ferroelectricity. The Goldschmidt tolerance factor is often used to quantify this balance between ionic sizes and predict structural stability.

Off-Center Displacement

A key mechanism underlying ferroelectric behavior in perovskites is the off-center displacement of ions. In ferroelectric materials like barium titanate, a larger A-site ion helps facilitate the displacement of the titanium ion within its octahedron, leading to a net dipole moment. Conversely, a smaller ion like strontium can restrict this displacement, stabilizing the centrosymmetric structure and thereby suppressing ferroelectricity.

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