Extensively studied PMN-PT and PIN-PMN-PT crystals with compositions close to the morphotropic phase boundary possess excellent piezoelectric characteristics. Recently developed alternating current treatment enhances the piezoelectric performance even further. Here, we demonstrate the results of studying the domain structure evolution by direct optical imaging during polarization reversal in [001]-oriented PIN-PMN-PT single crystals of rhombohedral phase during alternating current poling (ACP). The main types of domain structures involved in polarization reversal were revealed. Cross-like domain structure (CDS) was found to be undesirable for the piezoelectric application. The ACP-treatment proved to be effective in reducing the CDS fraction as a result of the growth of lens-shaped domains attributed to the 71° switching. The interaction of cross-like and lens-shaped domains was proposed as a key mechanism for improving the piezoelectric properties by the ACP-treatment. Comparison of the switching current with optical images revealed the correlation between the CDS area and electric field corresponding to the current maximum. This fact allows optimizing the number of the ACP-treatment pulses based on the switching current data without optical imaging.

Optical phased arrays (OPAs) encounter a formidable trade-off between performance and design due to the intricacies of their system. Here, we propose a cascaded domain engineering OPA structure via domain engineering. A six-layer cascaded domain engineering OPA prototype, consisting of 32 array elements, was designed, fabricated, and characterized. In contrast to the existing OPA scheme, only one control electronics is used to control the entire array elements, regardless of the number of array elements. The speed of beam steering is demonstrated up to 3 MHz in the bulk LiNbO3 (LN) demo, based on the fast response of the electro-optic crystal. Meantime, by demonstrating dynamic beam steering continually, its capability of continuous scanning and continually active phase tunability has been verified. The utilization of such cascaded domain engineering techniques provides a promising approach to OPA and related applications.

Relaxor-based ferroelectric crystals of lead magnesium niobate-lead titanate (PMN-PT) are attracting great attention due to their prominent piezoelectric properties. Moreover, an enhancement of the integral properties requires the deep understanding of domain kinetics and domain structure evolution for application of the domain engineering techniques in relaxor-PT materials. Here, we demonstrate the results of studying the domain structure evolution by direct optical imaging during polarization reversal in [111]-oriented rhombohedral PMN-PT single crystals. Three domain types involved in the switching process have been revealed. The following consequent stages of the domain structure evolution have been separated: (I) nucleation and growth of a↑-domains and 2a-CDW and (II) nucleation and growth of c↓-domains. The undesirable effect of the partial backswitching during the electric field decrease was attributed to the clamped switching conditions.

The possibility to control the charge, type, and density of domain walls allows properties of ferroelectric materials to be selectively enhanced or reduced. In ferroelectric–ferroelastic materials, two types of domain walls are possible: pure ferroelectric and ferroelastic–ferroelectric. In this paper, we demonstrated a strategy to control the selective ferroelectric or ferroelastic domain wall formation in the (111) single-domain rhombohedral PMN-PT single crystals at the nanoscale by varying the relative humidity level in a scanning probe microscopy chamber. The solution of the corresponding coupled electro-mechanical boundary problem allows explaining observed competition between ferroelastic and ferroelectric domain growth. The reduction in the ferroelastic domain density during local switching at elevated humidity has been attributed to changes in the electric field spatial distribution and screening effectiveness. The established mechanism is important because it reveals a kinetic nature of the final domain patterns in multiaxial materials and thus provides a general pathway to create desirable domain structure in ferroelectric materials for applications in piezoelectric and optical devices.

We have studied a dense domain structure (DDS) appearing during polarization reversal in rhombohedral (111)-cut lead magnesium niobate-lead titanate single crystals. The complicated shape of the switching current was explained by means of non-uniform motion of the boundary between the DDS and c-domains using comparative analysis of the optical current and kinetic map. 2D-vector piezoresponse force microscopy revealed that DDS represented needle-like a-domains inside the a-domains with different vertical orientations of spontaneous polarization.