Polymorphic characteristics challenging electrical properties in lead-free piezoceramics

Area of Science:

• Materials Science
• Solid State Physics
• Ceramics Engineering

Background:

• Potassium sodium niobate (KNN) ceramics exhibit temperature-dependent polymorphic phase transitions.
• These transitions lead to significant fluctuations in electrical properties, impacting device performance.
• Understanding the origins of these temperature sensitivities is crucial for KNN-based piezoceramics.

Purpose of the Study:

• Investigate the temperature-sensitive electrical properties of KNN-based piezoceramics.
• Elucidate the structure and physical origins of these temperature dependencies.
• Develop strategies for optimizing piezoelectric stability in KNN systems.

Main Methods:

• Analysis of temperature-dependent polymorphic phase transitions in KNN ceramics.
• Investigation of dielectric anomalies and their relation to local chemical heterogeneity.
• Measurement of electric field-induced maximum and remnant polarization.
• Evaluation of piezoelectric coefficients (d33 and d33*) at varying temperatures.

Main Results:

• The orthorhombic-tetragonal (O-T) phase transition shows a degenerate dielectric anomaly due to diffused phase transitions caused by additives.
• Elevated piezoelectric coefficients (d33 and d33*) were observed near the O-T transition.
• Fluctuations in piezoelectric properties are linked to the degeneration between maximum and remnant polarization.
• High and temperature-insensitive d33 (~385 pC/N) and d33* (~480 pm/V) were achieved in the rhombohedral-orthorhombic-tetragonal (R-O-T) region.

Conclusions:

• Optimizing piezoelectric stability involves shifting the O-T phase transition to near room temperature, creating R-O-T or R-T phase boundaries.
• Diffused phase transitions over a wide temperature range are key to enhancing stability.
• KNN ceramics with optimized phase boundaries demonstrate excellent temperature insensitivity for piezoelectric properties.