Unleashing pyroelectricity enhancement via phase transition-driven defect alignment in KNN-based ferroelectrics.

Area of Science:

• Materials Science
• Solid State Physics
• Ceramics Engineering

Background:

• The pyroelectric effect is crucial for thermal imaging and energy harvesting.
• Understanding defect dipole coupling with phase structures is key to advancing defect-engineered symmetry modulation.
• Current methods for enhancing pyroelectric performance through doping and composites have limitations.

Purpose of the Study:

• To investigate an abnormal pyroelectric phenomenon in potassium sodium niobate (KNN) ceramics.
• To explore the impact of poling temperature relative to the orthorhombic-to-tetragonal phase transition temperature (T_O-T) on the pyroelectric coefficient (p).
• To elucidate the underlying mechanisms responsible for enhanced pyroelectricity at high temperatures.

Main Methods:

• Utilizing potassium sodium niobate ceramics.
• Performing thermal poling experiments with varying poling temperatures, specifically above and below the T_O-T.
• Measuring the pyroelectric coefficient (p) at elevated temperatures.
• Proposing a dual mechanism involving rigid-ion displacement and defect dipole alignment.

Main Results:

• An abnormal pyroelectric phenomenon was observed where poling above T_O-T significantly increased the pyroelectric coefficient (p).
• The pyroelectric coefficient at 200°C reached 45.4 × 10^-4 C m^-2 K^-1 after high-temperature poling, a sevenfold increase compared to poling within the orthorhombic phase.
• This represents the highest reported pyroelectric value to date, demonstrating potential for high-temperature thermal sensing.
• A dual mechanism involving rigid-ion displacement and defect dipole alignment was proposed to explain the enhanced pyroelectricity.

Conclusions:

• High-temperature poling above the phase transition temperature is an effective strategy for significantly enhancing the pyroelectric properties of KNN ceramics.
• The proposed dual mechanism provides insight into optimizing pyroelectric materials for high-temperature applications.
• This work establishes a new paradigm for designing and engineering high-performance pyroelectric materials through symmetry-confined thermal poling.