Diffuse phase transitions and random-field-induced domain states of the ‘‘relaxor’’ ferroelectric ${\mathrm{PbMg}}_{1/3}$${\mathrm{Nb}}_{2/3}$${\mathrm{O}}_3$

The diffuseness of the ferroelectric phase transition in ${\mathrm{PbMg}}_{1/3}$ ${\mathrm{Nb}}_{2/3}$ ${\mathrm{O}}_3$ is proposed to be due to quenched random electric fields originating from charged compositional fluctuations. They are responsible for the extreme critical slowing down, the freezing into nanometric ferroelectric domains, and the slow relaxation of the polarization below ${\mathit{T}}_{\mathit{c}}$∼212 K. Barkhausen jumps during poling exclude glassiness, which was conjectured previously. At ${\mathit{T}}_{\mathit{c}}$ a ferroelectric anomaly of the dielectric permittivity appears, if the random fields are overcome by an external electric field.