Crystal Structure and Concentration-Driven Phase Transitions in Lu(1-x)ScxFeO3 (0 ≤ x ≤ 1) Prepared by the Sol-Gel Method.

The structural state and crystal structure of Lu(1-x)ScxFeO3 (0 ≤ x ≤ 1) compounds prepared by a chemical route based on a modified sol-gel method were investigated using X-ray diffraction, Raman spectroscopy, as well as scanning electron microscopy. It was observed that chemical doping with Sc ions led to a structural phase transition from the orthorhombic structure to the hexagonal structure via a wide two-phase concentration region of 0.1 < x < 0.45. An increase in scandium content above 80 mole% led to the stabilization of the non-perovskite bixbyite phase specific for the compound ScFeO3. The concentration stability of the different structural phases, as well as grain morphology, were studied depending on the chemical composition and synthesis conditions. Based on the data obtained for the analyzed samples, a composition-dependent phase diagram was constructed.

Local Polarization Reversal by Ion Beam Irradiation in SBN Single Crystals Covered by Dielectric Layer.

Formation of the domain structure by ion beam irradiation was studied in thermally depolarized Ce-doped strontium barium niobate single crystals covered by a dielectric layer. Three types of irradiation regimes were used: dot exposure, stripe exposure, and line exposure. The dependences of the domain size and depth on the irradiated dose were measured. The circular shape of the isolated domains with partially switched broad domain boundary was obtained. Isotropic domain growth was attributed to the step generation at the wall by merging with the residual nanodomains that appeared after thermal depolarization. The obtained linear dose dependence of the switched area was attributed to the screening of the depolarization field by the injected charge. The shape distortion of the domains growing in the neighborhood with already created ones was attributed to the electrostatic interaction of the approaching charged domain walls. The obtained results can be applied for the creation of precise domain patterns with arbitrary orientation and shape to produce nonlinear optical devices with improved characteristics, including electrically tunable diffractive optical elements.

Self-Organized Formation of Quasi-Regular Ferroelectric Nanodomain Structure on the Nonpolar Cuts by Grounded SPM Tip.

The understanding of self-organization processes at the micro- and nanoscale is of fundamental interest and is important to meet the great challenges in further miniaturization of electronic devices to the nanoscale. Here, we report self-organized quasi-regular nanodomain structure formation on the nonpolar cut of a ferroelectric lithium niobate single crystal. These structures were formed along the trajectory of grounded scanning probe microscope tip approaching or moving away from the freshly switched region. Detailed analysis of the formed structures revealed internal organization by the length of the needle-like domains, which ranged from uniform to quasi-periodic and even chaotic modes as a function of distance from the switched region. Comprehensive investigations and numerical simulations allowed to attribute explored phenomena to charge injection during the field application and further switching under the action of electric field induced by injected charges near the tip. Self-organization and quasi-periodicity were explained by the effective screening and long-range electrostatic interaction between the individual needle-like domains.

Dual strain mechanisms in a lead-free morphotropic phase boundary ferroelectric.

Electromechanical properties such as d33 and strain are significantly enhanced at morphotropic phase boundaries (MPBs) between two or more different crystal structures. Many actuators, sensors and MEMS devices are therefore systems with MPBs, usually between polar phases in lead (Pb)-based ferroelectric ceramics. In the search for Pb-free alternatives, systems with MPBs between polar and non-polar phases have recently been theorized as having great promise. While such an MPB was identified in rare-earth (RE) modified bismuth ferrite (BFO) thin films, synthesis challenges have prevented its realization in ceramics. Overcoming these, we demonstrate a comparable electromechanical response to Pb-based materials at the polar-to-non-polar MPB in Sm modified BFO. This arises from 'dual' strain mechanisms: ferroelectric/ferroelastic switching and a previously unreported electric-field induced transition of an anti-polar intermediate phase. We show that intermediate phases play an important role in the macroscopic strain response, and may have potential to enhance electromechanical properties at polar-to-non-polar MPBs.