Dielectric nonlinearity amd Raman scattering studies of the polarization state evolution in lead magnesium niobate

Abstract

Polarization state evolution in model ferroelectric with diffuse phase transition lead magnesium niobate has been studied. The results are given of the measurements of temperature dependences of dielectric permittivity ε, dielectric nonlinearity and Raman light scattering when a bias electric field E ₌ is applied to the crystal in different regimes. Two minima have been observed in temperature dependence of the second derivative of the ε with respect to the field E ₌(β) (E ₌ < 500 V/cm), the low-temperature minimum degenerated at E ₌ > 500 V/cm. Minima in β(T) probably correspond to phase transitions into cluster dipole glass-like state. The decrease of the intensity growth rate of the Raman scattering band at ∼50 cm⁻¹, J ₅₀ at crystal heating is observed near glass-like state phase transition temperatures. The anomalies in temperature dependences of ε(T) and J ₅₀ have been observed at macrodomenization of the crystal under field E ₌ and at macrodomain ferroelectric state destruction at further heating of the crystal. Some anomalies in ε(T) and J ₅₀(T) probably correspond to structural phase transition. The nature of polarization states in PMN is discussed.

Key Words:

• Keywords:
• diffuse phase transition
• glass-like state
• dielectric nonlinearity
• Raman scattering