A comparative study of structural and electrical properties in lead-free BCZT ceramics: Influence of the synthesis method

In the present work, various grain size phenomena were studied in promising lead-free piezoelectric ceramics (Ba0.85Ca0.15) (Zr0.10Ti0.90)O3 fabricated via chemical and conventional oxide methods. Phase composition was ascertained by the Rietveld refinement. Average grain size estimated from the microstructure was ∼1.5 μm in the sol-gel derived ceramic (SG-BCZT) which was much smaller than that obtained in coarse grained (∼27 μm) sample prepared by solid state method (SS-BCZT). Systematic investigation of various functional properties viz. dielectric, ferroelectric, piezoelectric and impedance emphasized the profound influence of grain size effects. The increase in grain boundary volume fraction enhanced diffuseness while lowered the dielectric peak in SG-BCZT. Similarly, increase in elastic stiffness and progressive hindrance to domain wall movements, resulted in a decrease of the remnant polarization and the associated piezoelectric charge coefficient values in small-grained SG-BCZT sample. Accordingly, higher Young's modulus value of 158.3 GPa was observed in SG-BCZT as compared to 117.9 GPa in SS-BCZT. Local-area piezoresponse force microscopy (PFM) images revealed lamellar domains with periodicity 250 ± 90 nm in SS-BCZT while small sized fractal-like irregular domains with an estimated domain width of 150 ± 60 nm were registered in SG-BCZT. Complex impedance spectroscopy results along with grain boundary conductivity were also guided by grain size effect. The mechanisms of grain size driven effects and their impact on the functional properties were discussed.publishe

Local Piezoelectric Properties of Doped Biomolecular Crystals

Piezoelectricity is the ability of certain crystals to generate mechanical strain proportional to an external electric field. Though many biomolecular crystals contain polar molecules, they are frequently centrosymmetric, signifying that the dipole moments of constituent molecules cancel each other. However, piezoelectricity can be induced by stereospecific doping leading to symme-try reduction. Here, we applied piezoresponse force microscopy (PFM), highly sensitive to local piezoelectricity, to characterize( 010) faces of a popular biomolecular material, α-glycine, doped with other amino acids such as L-alanine and L-threonine as well as co-doped with both. We show that, while apparent vertical piezoresponse is prone to parasitic electrostatic effects, shear piezoelectric activity is strongly affected by doping. Undoped α-glycine shows no shear piezoelectric response at all. The shear response of the L-alanine doped crystals is much larger than those of the L-threonine doped crystals and co-doped crystals. These observations are rationalized in terms of host–guest molecule interactions. © 2021 by the authors. Licensee MDPI, Basel, Switzerland.Funding: This work was supported by the collaborative program of the Israeli Ministry of Science with the Russian Foundation for Basic Research (RFBR), grant № 3-16492, and directly by the RFBR (grant № 19-52-06004 MNTI_a). The equipment of the Ural Center for Shared Use “Modern Nanotechnology” UrFU was used. A.K. acknowledges the Ministry of Science and Higher Education of the Russian Federation for the support under the project № 075-15-2021-588 from 1.06.2021. The work was also developed within the scope of the project CICECO at the Aveiro Institute of Materials, refs. UIDB/50011/2020 and UIDP/50011/2020, financed by national funds through the Portuguese Foundation for Science and Technology/MCTES. I.L. expresses his gratitude to the Estate of Olga Klein–Astrachan fund, grant № 721977

Tip-induced domain growth on the non-polar cuts of lithium niobate single-crystals

Currently, ferroelectric materials with designed domain structures are considered as a perspective material for new generation of photonic, data storage, and data processing devices. Application of external electric field is the most convenient way of the domain structure formation. Lots of papers are devoted to the investigation of domain kinetics on polar surface of crystals while the forward growth remains one of the most mysterious stages due to lack of experimental methods allowing to study it. Here, we performed tip-induced polarization reversal on X- and Y-non-polar cuts in single-crystal of congruent lithium niobate which allows us to study the forward growth with high spatial resolution. The revealed difference in the shape and length of domains induced on X- and Y-cuts is beyond previously developed theoretical approaches used for the theoretical consideration of the domains growth at non-polar ferroelectric surfaces. To explain experimental results, we used kinetic approach with anisotropy of screening efficiency along different crystallographic directions. © 2015 AIP Publishing LLC

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. © 2020 by the authors. Licensee MDPI, Basel, Switzerland.Instituto Nacional de Ciência e Tecnologia para Excitotoxicidade e Neuroproteção, INCT-EN: UID/04564/2020, UIDB/50011/2020, UIDP/50011/2020Russian Science Foundation, RSF: 18-19-00307Funding: This work was supported by the RSF (project #18-19-00307). Investigations performed at the Center for Physics of the University of Coimbra were supported by Fundação para a Ciência e a Tecnologia (project UID/04564/2020). M.V.S. acknowledges Russian academic excellence project “5-100” for Sechenov University. Part of work done at the University of Aveiro was developed within the scope of the project CICECO-Aveiro Institute of Materials, refs. UIDB/50011/2020 & UIDP/50011/2020, financed by national funds through the FCT/MEC

Self-organized growth of dendrite domains in lithium niobate and lithium tantalate single crystals

The equipment of the Ural Center for Shared Use “Modern nanotechnology” UrFU was used. The research was made possible by Russian Science Foundation (Project №14-12-00826)

Local polarization reserval in waveguides created in lithium niobate single crystals by high energy ion irradiation

The equipment of the Ural Center for Shared Use “Modern Nanotechnology” Ural Federal University has been used

Temperature Effect on the Stability of the Polarized State Created by Local Electric Fields in Strontium Barium Niobate Single Crystals

AbstractThe stability of ferroelectric domain patterns at the nanoscale has been a topic of much interest for many years. We investigated the relaxation of the polarized state created by application of a local electric field using a conductive tip of a scanning probe microscope for the model uniaxial relaxor system SrxBa1−xNb2O6 (SBN) in its pure and Ce-doped form. The temporal relaxation of the induced PFM contrast was measured at various temperatures. The average value of the induced contrast decreases during heating for all investigated crystals. Below the freezing temperature the induced state remains stable after an initial relaxation. Above the freezing temperature the induced state is unstable and gradually decays with time. The stability of the induced state is strongly affected by the measuring conditions, so continuous scanning results in a faster decay of the poled domain. The obtained effects are attributed to a decrease of the induced polarization and backswitching of the polarized area under the action of the depolarization field.</jats:p

Local electromechanical properties of barium strontium titanate based glass-ceramics

The equipment of the Ural Center for Shared Use “Modern Nanotechnology” Ural Federal University was used. The research was made possible by Russian Foundation for Basic Research (Grant 18-52-53032)