Antiferroelectrics are essential ingredients for the widely applied piezoelectric and ferroelectric materials: the most common ferroelectric, lead zirconate titanate is an alloy of the ferroelectric lead titanate and the antiferroelectric lead zirconate. Antiferroelectrics themselves are useful in large digital displacement transducers and energy-storage capacitors. Despite their technological importance, the reason why materials become antiferroelectric has remained allusive since their first discovery. Here we report the results of a study on the lattice dynamics of the antiferroelectric lead zirconate using inelastic and diffuse X-ray scattering techniques and the Brillouin light scattering. The analysis of the results reveals that the antiferroelectric state is a 'missed' incommensurate phase, and that the paraelectric to antiferroelectric phase transition is driven by the softening of a single lattice mode via flexoelectric coupling. These findings resolve the mystery of the origin of antiferroelectricity in lead zirconate and suggest an approach to the treatment of complex phase transitions in ferroics.

We report the results of comprehensive study of the critical dynamics of the prototype perovskite antiferroelectric PbZrO3. The combination of inelastic X-ray and diffuse X-ray scattering techniques and Brillouin light scattering was used. It is found that the dispersion of the TA phonons is strongly anisotropic. The dispersion curve of the in-plane polarized TA phonons propagating in [1 1 0] direction demonstrates pronounced softening. Slowing down of the excitations at R-point is found, it is manifested in growing of the central peak. This slowing down is too weak to be considered as a primary origin of the corresponding order parameter. Obtained results are treated in terms of TA-TO flexoelectric mode coupling. It is demonstrated that the structural phase transformation in PbZrO3 can be considered as the result of the only intrinsic instability associated with the ferroelectric soft mode.

the paraelectric to AFE phase transition, cell quadrupling in PbZrO 3 results in the appearance of TBs. These boundaries are characterized by translation vectors R = [ a / n 1 , b / n 2 , c / n 3 ], 1/ n i ( i = 1, 2, 3), which are fractions of the unit-cell translation vectors. In this work, we report on the relation between formation of polar TBs and the interfacial strain in the system of PbZrO 3 thin fi lms grown on SrTiO 3 substrates. In combination with geometric phase analysis (GPA), [ 28 ] high-angle annulardark-fi eld (HAADF) imaging and Stripe scanning transmission electron microscopy (STEM) techniques based on aberrationcorrected STEM allowed us to determine the structural arrangement and strain distribution near the interfaces.Epitaxial PbZrO 3 thin fi lms were grown on (100) SrTiO 3 substrate and on BaZrO 3 -buffered (100) SrTiO 3 substrate (see the Experimental Section for details). As the lattice parameters of PbZrO 3 are larger than that of SrTiO 3 , the BaZrO 3 buffer layer is used to modulate the misfi t between the PbZrO 3 fi lm and the SrTiO 3 substrate. Figure 1 a shows a plan-view bright-fi eld TEM image of a PbZrO 3 fi lm on BaZrO 3 buffered (100) SrTiO 3 substrate. The dark dot contrast in the image originates from threading dislocations in the fi lm arising from the threading segments associated with the misfi t dislocations due to the lattice mismatch. The HAADF-STEM image of the cross-sectional sample (Figure 1 b) shows morphology of the fi lm system with ≈35 nm thick PbZrO 3 fi lm. In the medium-magnifi ed HAADF image, Figure 1 c, one can clearly see that the PbZrO 3 fi lm is epitaxially grown on the BaZrO 3 buffer layer. Due to antiparallel displacements of Pb atoms and antiphase rotation of the octahedra, [ 29,30 ] the AFE structure characterized by the (010) and (021) refl ections, which are the superstructure refl ections of q Σ = 1/4(110) p and q R = 1/2(111) p with respect to the pseudocubic structure, [ 31 ] can clearly be identifi ed from the fast Fourier transformation (FFT) image illustrated in Figure 1 d. Considering that the image intensities are atomic-number dependent and roughly proportional to Z 2 , [ 32 ] the TBs residing inside the AFE domain areas can be directly observed based on the antiparallel displacements of the heavy Pb atoms along the orthorhombic [100] direction. A typical APB on the atomic scale, type R III-1 = 1/4 [02 n ] ( n = 0 or 2) is shown in Figure 1 e.Based on atomic scale investigation and analysis of GPA on the HAADF images, all types of TBs in the AFE PbZrO 3 thin fi lms were studied and the results are given in Table 1 . Figure 2 a shows the morphology of two types of TBs, the R III-1 and R I-1 = 1/4 [21 n ] type boundaries, in the 35 nm thick fi lm. The characteristic displacements of the Pb atoms are displayed as a function of the distance away from the boundary centers in Figure 2 b. Based on the average displacements (33.1 pm) of the Pb atoms away from their ideal positions, the spontaneous polarization is estimated as P S = 16 and 17 µC cm ...

Antiphase boundaries (APBs) are unique domain walls that may demonstrate switchable polarization in otherwise non-ferroelectric materials such as SrTiO3 and PbZrO3. The current study explores the possibility of displacing such domain walls at the nanoscale. We suggest the possibility of manipulating APBs using the inhomogeneous electric field of an Atomic Force Microscopy (AFM) tip with an applied voltage placed in their proximity. The displacement is studied as a function of applied voltage, film thickness, and initial separation of the AFM tip from the APB. It is established, for example, that for films with thickness of 15 nm, an APB may be attracted under the tip with a voltage of 25 V from initial separation of 30 nm. We have also demonstrated that the displacement is appreciably retained after the voltage is removed, rendering it favorable for potential applications.

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