Coexistence States near the Morphotropic Phase Boundary: II. The Scaling of the Free Energy in PbZr_1-xTi_xO₃

Abstract

A model of coexistence states due to the stable and metastable phases near the morphotropic phase boundary in perovskite-type ferroelectrics was proposed on the basis of the Landau–Devonshire free energy with the scaled parameter values in our previous paper [M. Iwata and Y. Ishibashi: Jpn. J. Appl. Phys. 51 (2012) 09LE03]. Here, the scaling method for the Landau–Devonshire free energy is discussed to clarify the correspondence relation between the scaled and real parameter systems. A new set of scaled parameter values for PbZr1-x Ti x O3 (PZT) is proposed on the basis of the real parameters reported by Haun et al. [Ferroelectrics 99 (1989) 45]. Using our scaled parameter values, the stable and metastable regions in the tetragonal and rhombohedral phases under equilibrium in PZT are clarified.

Electric field effect of relaxor ferroelectric (1 − x)Pb(Mg1/3Nb2/3)O3–xPbTiO3 crystals near morphotropic phase boundary composition probed by Brillouin scattering

“…24) Iwata et al have proposed that under the electric field, the effective domain-wall size increases near the MPB composition and the regions of the metastable R (T) phase becomes the thick domain walls of the stable T (R) phase on the coexistence states. 21,22) The strong negative correlation between the electrical response and the crystal coherence length at the sub-µm scale was also reported. 25) Recently, the electric field dependences of the perovskite ferroelectrics in relation to the critical end point (CEP) were studied, and the enhancement of the dielectric response was observed.…”

“…Upon the removal of the electric field, M A phase appears instead of R phase 19) which is different from PZN-8%PT, where M C phase recovers after removal of the electric field instead of M A phase. 18) On the other hand, the inhomogeneity in the relaxor ferroelectrics was discussed to explain the huge electrical response by multidomain states, 20) the coexistence states of R and T phases, 21,22) an adaptive phase that consists of nanodomains, 23) and the rotation of local polarizations. 24) Iwata et al have proposed that under the electric field, the effective domain-wall size increases near the MPB composition and the regions of the metastable R (T) phase becomes the thick domain walls of the stable T (R) phase on the coexistence states.…”

Curie constant in relaxor ferroelectrics Pb(Zn1/3Nb2/3)O3–8%PbTiO3

“…[8][9][10][11][12][13][14][15] A semiquantitative analysis of such phase diagrams using the Landau-Devonshire free energy was presented. [16][17][18] In our previous studies, [12][13][14][15] we also found that the diffuseness of the phase transition in PZN-xPT considerably decreases when the dc biasing field is applied, implying that reduced heterogeneity owing to the application of electric field may make the phase transition sharp, and concluded that the physical properties of relaxors in the PZN-xPT become more similar to those of normal ferroelectrics under the dc biasing field. 12) This indicates that the Landau-Devonshire free energy should be applicable to explain the phase transition in PZN-xPT under an electric field.…”

Dielectric tunability in Pb(Sc1/2Ta1/2)O3single crystals

“…[13][14][15][16][17][18][19] Ishibashi and Iwata proposed a theoretical model for such physical properties near the MPB based on the Landau-Devonshiretype free energy, where the dielectric permittivity perpendicular to the spontaneous polarization becomes extremely high, since the anisotropy of the free energy in the parameter space decreases. [20][21][22] In a series of our previous studies, we found that the ferroelectric critical endpoint (CEP) exists on the temper-ature-field phase diagram in the PZN-xPT system, 18) and that PZN-xPT near the CEP indicates a dielectric tunability higher than 90%, although unfortunately the operation temperature is much higher than room temperature. 23) We pointed out that a high dielectric tunability appears above the second-order phase transition temperature and critical temperature.…”