Chemically induced renormalization phenomena in Pb-based relaxor ferroelectrics under high pressure

Area of Science:

• Materials Science
• Solid State Physics
• Crystallography

Background:

• Lead scandium tantalate (PST) and lead scandium niobate (PSN) are perovskite relaxors exhibiting complex phase transitions under pressure.
• Understanding these transitions is crucial for tailoring material properties for advanced applications.
• Previous studies focused on pure PST and PSN, with limited analysis on heavily doped systems.

Purpose of the Study:

• To investigate the pressure-induced phase transition sequence in heavily doped PST and PSN relaxors.
• To analyze the structural phenomena occurring above the first phase transition (relaxor to non-polar rhombohedral).
• To determine the impact of A-site and B-site doping on critical transition pressures and structural ordering.

Main Methods:

• In situ synchrotron X-ray diffraction up to 25 GPa.
• In situ Raman spectroscopy up to 25 GPa.
• Analysis of PST doped with Nb5+ and Sn4+ (B-site), and Ba2+, La3+ (A-site); PSN doped with Sr2+, La3+ (A-site).

Main Results:

• All doped samples exhibit a second pressure-induced phase transition (pc2) similar to pure PST and PSN.
• Doping with Nb5+ or Sn4+ on B-sites increases pc2; Nb5+ doping reduces antipolar Pb2+ order coherence.
• A-site doping with Ba2+ increases pc2 by suppressing antipolar Pb2+ order; smaller cations generally favor ordering, but aliovalent doping reduces it.

Conclusions:

• The study elucidates the complex interplay between doping, pressure, and structural transitions in perovskite relaxors.
• Specific doping strategies can tune the critical pressures and the nature of the high-pressure phases.
• Dynamic compressibility is higher in the pressure range between the first and second transitions and decreases with disturbed antipolar order.