What defines a ferroelectric material?

Spontaneous polarization that can be reversed by an applied field, with a P-E hysteresis loop

Polarization only under mechanical stress

Zero polarization at all fields

Magnetization reversible by a field

What is the direct piezoelectric effect?

Polarization or voltage developed when the crystal is mechanically stressed

Shape change under an electric field

Spontaneous polarization at zero stress

Which statement about the two classes is correct?

Every ferroelectric is also piezoelectric, but quartz is piezoelectric and not ferroelectric

Every piezoelectric is ferroelectric

Piezoelectrics show hysteresis, ferroelectrics do not

Asked 2/28
2075 Asoj · 4 marks
2072 Kartik · 4 marks

Ferroelectricity versus piezoelectricity

Short answer

Ferroelectricity is spontaneous reversible polarization with P–E hysteresis, lost above Curie temperature (e.g., BaTiO3). Piezoelectricity generates polarization under stress and deformation under field in non-centrosymmetric crystals (e.g., quartz). Both lack symmetry centre; every ferroelectric is piezoelectric but not vice versa—ferroelectrics have high permittivity and hysteresis, piezoelectrics show linear stress–polarization and no Curie point.

What is ferroelectricity and piezoelectricity? Write their similarities and differences.

Ferroelectricity is the property of some crystals to have a spontaneous polarization (permanent net dipole moment) even without an applied field, whose direction can be reversed by an external field. They show a P-E hysteresis loop and lose this property above the Curie temperature $T_C$ . Examples: barium titanate (BaTiO₃, $T_C \approx 120°\text{C}$ ), Rochelle salt, PZT.

Piezoelectricity is the property of some crystals to develop electric polarization (and a voltage) when mechanically stressed (direct effect), and to change shape when an electric field is applied (converse effect). It needs a crystal with no centre of symmetry. Examples: quartz, PZT, Rochelle salt, ZnO.

Similarities

Both occur only in crystals without a centre of symmetry (non-centrosymmetric).
Both are linked to displacement of ions creating dipoles.
Every ferroelectric is also piezoelectric (and pyroelectric).
Both are used in transducers, sensors and capacitors; PZT is both.

Differences

Point	Ferroelectric	Piezoelectric
Polarization source	Spontaneous, present without field	Induced by mechanical stress
P with no stress, no field	Non-zero	Zero
Hysteresis (P–E loop)	Yes	No (linear P vs stress)
Curie temperature	Lost above $T_C$	Non-ferroelectric ones (e.g. quartz) have no Curie point
Relative permittivity	Very high (1000–10 000)	Moderate (quartz ~4.5)
Relation	Subset of piezoelectrics	Wider class (quartz is not ferroelectric)
Uses	Capacitors, FeRAM memory	Crystal oscillators, microphones, ultrasonic transducers, gas lighters

  P                    P
  ^   ____             ^      /
  |  /   /             |     /  slope = d
 -+-/---/--> E        -+----/----> stress
  |/___/               |   /
 Ferroelectric loop    Piezoelectric line

✓ Answer checked by Claude Opus 5.5 (high effort)

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Ferroelectricity versus piezoelectricity

Similarities

Differences

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