Antiferroelectric-like Behavior in a Lead-Free Perovskite Layered Structure Ceramic.

Area of Science:

• Materials Science
• Solid State Physics
• Crystallography

Background:

• Antiferroelectric (AFE) materials are crucial for energy storage and conversion, typically exhibiting double polarization-electric field (P-E) hysteresis loops and nonpolar structures.
• Perovskite layered structure (PLS) materials are a focus for lead-free alternatives, but their electrical behavior in relation to AFE characteristics is not fully understood.

Purpose of the Study:

• To investigate the unusual electrical behavior of lead-free PLS materials Sr1.68La0.32Ta1.68Ti0.32O7 (STLT32), Sr1.64La0.36Ta1.64Ti0.36O7 (STLT36), and Sr1.85Ca0.15Ta2O7 (SCT15).
• To characterize the observed AFE-like double P-E hysteresis loops in these polar PLS materials across a range of electric fields and temperatures.

Main Methods:

• Synthesis and characterization of lead-free PLS materials.
• Electrical measurements including polarization-electric field (P-E) hysteresis loops and variable-temperature dielectric spectroscopy.
• Structural analysis using neutron diffraction and piezoresponse force microscopy.
• Thermal analysis (e.g., DSC/TGA) to identify phase transitions.
• Microwave dielectric property measurements using a coplanar waveguide transmission line.

Main Results:

• STLT32, STLT36, and SCT15, despite having polar crystal structures, exhibit AFE-like double P-E hysteresis loops over wide electric field and temperature ranges.
• Neutron diffraction and piezoresponse force microscopy suggest STLT32 should be ferroelectric, indicating a dominant weakly polar phase with field-induced transitions.
• STLT32 shows two phase transitions around 250 °C and 750 °C, with the higher transition involving structural changes (octahedral tilting, perovskite block width, interlayer gap) and a shift from non-centrosymmetric to centrosymmetric structures.
• Microwave dielectric measurements reveal stable permittivity and low loss in STLT32 ceramic from 1 kHz to 20 GHz.

Conclusions:

• This study reports the first observation of AFE-like double hysteresis loops in PLS-type materials with polar crystal structures.
• The findings challenge conventional understanding of AFE behavior and suggest complex phase dynamics in these lead-free materials.
• The stable microwave dielectric properties of STLT32 make it a promising candidate for high-frequency electronic applications.