Ferroelectrics – spontaneous polarization State whether the following is correct: “Spontaneous polarization (a remanent electric dipole alignment without external field) occurs in ferroelectric materials.”

Introduction / Context:
Ferroelectric materials (e.g., BaTiO3, Pb(Zr,Ti)O3) possess a spontaneous electric polarization that can be reversed by an applied electric field, similar to ferromagnetism in magnetic materials. This property underpins non-volatile memories, high-permittivity capacitors, actuators, and sensors.

Given Data / Assumptions:

• Material exhibits a non-centrosymmetric crystal phase below its Curie temperature T_C.
• Domains of aligned dipoles form to minimize electrostatic energy, giving macroscopic polarization when poled.
• No external electric field is necessary to sustain the spontaneous polarization in the ferroelectric phase.

Concept / Approach:

In the ferroelectric phase (T < T_C), the free-energy landscape favors a finite polarization P_s in zero field. Domains with ±P_s exist; an external field can switch domain orientation, producing a hysteresis loop in the P–E plane. Above T_C, the material becomes paraelectric and spontaneous polarization vanishes. Therefore, the statement that spontaneous polarization occurs in ferroelectrics is correct (with the implicit understanding that it pertains to the ferroelectric phase).

Step-by-Step Solution:

Verification / Alternative check:

Polarization–electric field hysteresis measurements show remanent polarization and coercive field, directly evidencing spontaneous polarization in the ferroelectric state.

Why Other Options Are Wrong:

(b) contradicts the defining property. (c) adds an explicit temperature caveat that, while physically accurate, is not part of the original sentence; the base statement remains true as a general description of ferroelectrics. (d) confuses piezoelectricity (which many ferroelectrics also have) with ferroelectricity. (e) spontaneous polarization does not require stress.

Common Pitfalls:

Equating “spontaneous” with “permanent” irrespective of temperature or domain state; domain engineering and poling history matter for observed macroscopic polarization.

Final Answer:

True