relaxorferroelectric

Relaxor ferroelectrics are a class of ferroelectric materials characterized by a diffuse, frequency-dependent dielectric anomaly rather than a sharp ferroelectric transition. They typically crystallize in a perovskite structure ABO3 with substantial disorder on the B-site, produced by mixing cations such as Mg2+ and Nb5+ in PMN or Zn2+ and Nb5+ in PZN.

Key signatures include a broad maximum in the dielectric permittivity that shifts with measuring frequency, strong dielectric dispersion, and the absence of long-range ferroelectric order at temperatures below the Burns temperature TB. Polar nanoregions form well above the macroscopic transition and interact with the surrounding non-polar matrix, leading to relaxational dynamics described by a broad distribution of relaxation times and sometimes Vogel-Fulcher behavior.

Common relaxor compositions include lead magnesium niobate (PMN), lead zinc niobate (PZN), and their solid solutions with lead titanate (PT), such as PMN-PT and PZN-PT, which exhibit very large electromechanical coupling near morphotropic phase boundaries.

Properties often include large dielectric constants, strong piezoelectric coefficients, and enhanced electromechanical coupling, though long-range ferroelectric order is not inherent without external fields or compositional tuning. The materials are widely used in actuators, sensors, sonar transducers, capacitors, and tunable devices.

Challenges include understanding the microscopic origin of polar nanoregions and the relationship between local structure and macroscopic responses. Research continues to optimize compositions, processing, and temperature stability for applications.