Martensitelike spontaneous relaxor-normal ferroelectric transformation in Pb(Zn1∕3Nb2∕3)O3–PbLa(ZrTi)O3 system

The spontaneous relaxor-normal ferroelectric transformation was found in the tetragonal composition of $\mathrm{Pb}\left({\mathrm{Zn}}_{1∕3}{\mathrm{Nb}}_{2∕3}\right){\mathrm{O}}_3–\mathrm{Pb}\mathrm{La}\left(\mathrm{Zr}\mathrm{Ti}\right){\mathrm{O}}_3$ (0.3PZN–0.7PLZT) complex $\mathrm{AB}{\mathrm{O}}_3$ system. The corresponding dielectric permittivities and losses of different compositions located near the morphotrophic phase boundary were analyzed. By reviewing all of the results about this type of transformation in previous references, the electric, compositional, structural, and thermodynamic characteristics of the spontaneous relaxor-normal transformation were proposed. Additionally, the adaptive phase model for martensite transformation proposed by Khachaturyan et al. [Phys. Rev. B 43, 10832 (1991)] was introduced into this ferroelectric transformation to explain the unique transformation pathway and associated features such as the tweedlike domain patterns and the dielectric dispersion under the critical transition temperature. Due to the critical compositions near the MPB, the ferroelectric materials just fulfill the condition, in which the adaptive phases can form in the transformation procedure. The formation of the adaptive phases, which are composed of stress-accommodating twinned domains, makes the system bypass the energy barrier encountered in conventional martensite transformations. The twinned adaptive phase corresponds to the tweedlike domain pattern under a transmission electronic microscope. At lower temperature, these precursor phases transform into the conventional ferroelectric state with macrodomains by the movement of domain walls, which causes a weak dispersion in dielectric permittivity.