Problem 46 - A Complete Resource Book in Chemistry for JEE Main

Question

An example of ferroelectric substance is (a) Tourmaline (b) Quartz (c) Barium titanate (d) Lead zirconate

Step-by-Step Solution

Answer

The correct answer is (c) Barium titanate.

Step 1: Understanding Ferroelectric Substances

Ferroelectric substances are materials that display a spontaneous electric polarization that can be reversed by an external electric field. They have permanent electric dipoles which can be aligned by applying a suitable electric field.

Step 2: Analyzing Option (a): Tourmaline

Tourmaline is a crystal silicate mineral that is not usually classified as ferroelectric. It is piezoelectric, meaning it generates a voltage when mechanical stress is applied, but does not have the reversible electric polarization characteristic of ferroelectric materials.

Step 3: Analyzing Option (b): Quartz

Quartz is another piezoelectric material commonly found in watches and electronics for its frequency stability. While it shows piezoelectric properties, it does not demonstrate the essential ferroelectric behavior of reversible polarization with an applied electric field.

Step 4: Analyzing Option (c): Barium Titanate

Barium titanate (BaTiO3) is a well-known ferroelectric material. It has a perovskite crystal structure that allows it to exhibit spontaneous polarization and change polarization direction when an electric field is applied.

Step 5: Analyzing Option (d): Lead Zirconate

Lead zirconate is part of the lead zirconate-titanate (PZT) family, known for its piezoelectric properties. However, lead zirconate itself is anti-ferroelectric, not exhibiting the typical characteristics of ferroelectric substances independently.

Step 6: Conclusion: Identifying the Ferroelectric Substance

Considering the definitions and properties, Barium titanate (Option c) is the correct example of a ferroelectric substance, as it exhibits the unique characteristics of spontaneous and reversible polarization with an applied electric field.

Key Concepts

Spontaneous Polarization

In the world of ferroelectric substances, spontaneous polarization is a fascinating and essential property. This phenomenon occurs without the need for an external electric field, meaning the material inherently possesses a electric polarization. This is due to the unique arrangement of atoms within the ferroelectric material's crystal structure. As a result, certain atoms carry a slight electric charge.

A key feature of spontaneous polarization is the presence of permanent electric dipoles. These dipoles can align themselves in a certain direction, even when no external influence is applied. For ferroelectric materials, the temperature plays a significant role. When the material is below a certain critical temperature, known as the Curie temperature, spontaneous polarization takes place.

Importantly, this inherent polarization in ferroelectric substances can be modified or reversed. All it requires is the application of an external electric field. This reversible quality marks the critical difference between ferroelectric and other dielectric materials.

Reversible Polarization

Ferroelectric materials, like barium titanate, are unique due to their reversible polarization. This means that the direction of the electric polarization in these materials can change when exposed to an external electric field. This characteristic is extremely useful in applications such as memory storage and sensors.

When an external electric field is applied to a ferroelectric material, the dipoles within the material realign themselves to match the direction of the field. Once the field is removed, the dipoles can return to their original alignment or maintain the new alignment, depending on the material's properties.

• This ability to reverse polarization is what enables ferroelectric substances to act as capacitors with memory, storing information in the form of electric charges.
• Reversible polarization also contributes to the versatility and efficiency of piezoelectric devices, which convert mechanical signals to electric signals.

The process of polarization reversal is a hallmark of ferroelectric materials, distinguishing them from non-ferroelectric dielectrics.

Barium Titanate

Barium titanate, symbolized as BaTiO\( _3 \), is a prominent example of a ferroelectric material distinguished for its notable properties. It comes with a perovskite crystal structure, which provides its characteristic ferroelectric behavior. The structure consists of a Ba and Ti ion at the center, surrounded by oxygen ions. The slight displacement of these ions under certain conditions results in spontaneous polarization.

The interesting aspect of barium titanate is its phase transitions. It undergoes changes at different temperatures, affecting its crystal symmetry and, thus, its polarization. Below its Curie temperature, the structure becomes tetragonal, allowing spontaneous polarization and reversible polarization characteristics to emerge fully.

• In practical applications, barium titanate is widely used in capacitors, electromechanical devices, and non-volatile ferroelectric random-access memory (FRAM) due to its strong dielectric properties.
• It serves as an essential material in research to develop new ferroelectric compounds with improved properties.

Overall, barium titanate remains a cornerstone in the study and application of ferroelectric materials, making it an ideal model for understanding ferroelectricity.