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.

Peculiarities of the Crystal Structure Evolution of BiFeO3-BaTiO3 Ceramics across Structural Phase Transitions.

Evolution of the crystal structure of ceramics BiFeO3-BaTiO3 across the morphotropic phase boundary was analyzed using the results of macroscopic measuring techniques such as X-ray diffraction, differential scanning calorimetry, and differential thermal analysis, as well as the data obtained by local scale methods of scanning probe microscopy. The obtained results allowed to specify the concentration and temperature regions of the single phase and phase coexistent regions as well as to clarify a modification of the structural parameters across the rhombohedral-cubic phase boundary. The structural data show unexpected strengthening of structural distortion specific for the rhombohedral phase, which occurs upon dopant concentration and temperature-driven phase transitions to the cubic phase. The obtained results point to the non-monotonous character of the phase evolution, which is specific for metastable phases. The compounds with metastable structural state are characterized by enhanced sensitivity to external stimuli, which significantly expands the perspectives of their particular use.

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.

Symmetry breaking and electrical frustration during tip-induced polarization switching in the nonpolar cut of lithium niobate single crystals.

Polarization switching in ferroelectric materials is governed by a delicate interplay between bulk polarization dynamics and screening processes at surfaces and domain walls. Here we explore the mechanism of tip-induced polarization switching at nonpolar cuts of uniaxial ferroelectrics. In this case, the in-plane component of the polarization vector switches, allowing for detailed observations of the resultant domain morphologies. We observe a surprising variability of resultant domain morphologies stemming from a fundamental instability of the formed charged domain wall and associated electric frustration. In particular, we demonstrate that controlling the vertical tip position allows the polarity of the switching to be controlled. This represents a very unusual form of symmetry breaking where mechanical motion in the vertical direction controls the lateral domain growth. The implication of these studies for ferroelectric devices and domain wall electronics are discussed.

Formation of nanodomain structures during polarization reversal in congruent lithium niobate implanted with Ar ions.

We present the experimental study of the formation of self-similar nanodomain structures during polarization reversal in single-crystalline congruent lithium niobate (CLN) implanted by Ar ions. The formed dense surface nanodomain structure with charged domain walls differs drastically from the growth of the hexagonal domains in unimplanted CLN. The lack of wall shape stability during sideways domain wall motion was revealed. The analysis of the domain structure images in the bulk, obtained by Raman confocal microscopy, revealed the main stages of the domain structure evolution starting at unimplanted polar surface and consisting of nanodomain chain elongation, merging of isolated domains, and domain widening. The switching current data has been fitted by modification of Kolmogorov-Avrami formula for switching in a linearly increasing field. The observed experimental facts have been attributed to formation of an amorphous thin surface layer and increase of the bulk conductivity resulting from oxygen out-diffusion under radiation heating in vacuum during ion implantation. The formation of the experimentally obtained abnormal domain shapes has been explained while taking into account the step generation at the domain wall in the bulk during switching in a low electric field.