Direct Measurement of Piezoelectric Response around Ferroelectric Domain Walls in Crystals with Engineered Domain Configuration

We report the first investigation of the piezoelectric response on a nanoscale in the poled ferroelectric crystals with engineered configuration of domains. Piezoresponse force microscopy of tetragonal 0.63PMN-0.37PT relaxor-based ferroelectric crystals reviled that the d33 piezoelectric coefficient is significantly reduced within the distance of about 1 um from the uncharged engineered domain wall. This finding is essential for understanding the mechanisms of the giant piezoresponse in relaxor-based crystals and for designing new piezoelectric materials

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

Molecular modeling of ZnO nanoclusters interacting with various dopant and PVDF

Authors wish to acknowledge the Russian Foundation for Basic Researches (RFBR) grant # 19-01-00519 А

Insights into improved ferroelectric and electrocaloric performance of Ba0.85Ca0.15Ti0.9Zr0.1O3 thick films grown by the electrophoretic deposition

Lead-free Ba0.85Ca0.15Ti0.9Zr0.1O3 (BCZT) bulk ceramics have recently gained attention as one of the attractive candidates for electrocaloric cooling due to their large heat absorption capacity induced by electro-structural phase transition near room temperature. However, adiabatic temperature change (ΔT) at room temperature in ceramics has been limited by their relatively low dielectric breakdown strength. Thick films, in this respect, possess the advantages of ceramics (volume) and thin films (thickness). In this work, a systematic ferroelectric and electrocaloric investigation of BCZT thick films, fabricated by electrophoretic deposition combined with laser annealing, has been carried out. Laser annealing at an optimized energy density of 398 W/cm2 has resulted in densely packed grain morphology with no compositional heterogeneities. Analysis of the scaling behavior of dynamic hysteresis revealed that ferroelectric domain reversal in BCZT/Pt has good stability and low energy consumption in the saturation region. The present thick films exhibited larger breakdown strength of 294 kV/cm and recoverable energy storage density of ~7.3 J/cm3 , at least five-fold enhancement compared to the bulk which is stable up to a 4 mm bending radius. The indirect electrocaloric measurements displayed parameters such as a ΔT and entropy change (ΔS) of 2.94 K and 3.1 J kg− 1 K− 1 respectively, for 205 kV/cm which are more than two orders increased compared to the bulk. Higher values of ΔT (1.9 K) at 25 ◦C, refrigerant capacity of 249 J/kg, and responsivity of 0.143 K mm/kV for BCZT/Pt film compared to relevant lead-free ferroelectric thick films elucidate the potential use of these films for solid-state refrigeration applications. The work also presents electrophoretic deposition with laser annealing as an alternative technique to widely studied tape-casting of thick films for electrocaloric studies.publishe

Imprint effect in PZT thin films at compositions around the morphotropic phase boundary

Piezoeresponse force microscopy (PFM) and local piezoresponse hysteresis loops were used to study the imprint effect in PbZr1-xTixO3 thin films at compositions around the morphotropic phase boundary (MPB). Schottky barriers and mechanical coupling between film-substrate were excluded as origin for the imprint in these films. Comparing the composition dependence of the effective d33 before poling with some reports in the literature, the existence of point defects such as complex vacancies (Vpb.., VO.. and Vpb..-VO..) and Ti3+ centers is discussed as probable origin for the imprint effect observed here. © 2016, © Taylor & Francis Group, LLC

Thickness dependence of structure and piezoelectric properties at nanoscale of polycrystalline lead zirconate titanate thin films

Lead zirconate titanate Pb(Zr0.50Ti0.50)O-3 (PZT) thin films were deposited by a polymeric chemical method on Pt(111)/Ti/SiO2/Si substrates to understand the mechanisms of phase transformations and the effect of film thickness on the structure, dielectric, and piezoelectric properties in these films. PZT films pyrolyzed at temperatures higher than 350 degrees C present a coexistence of pyrochlore and perovskite phases, while only perovskite phase grows in films pyrolyzed at temperatures lower than 300 degrees C. For pyrochlore-free PZT thin films, a small (100)-orientation tendency near the film-substrate interface was observed. Finally, we demonstrate the existence of a self-polarization effect in the studied PZT thin films. The increase of self-polarization with the film thickness increasing from 200 nm to 710 nm suggests that Schottky barriers and/or mechanical coupling near the film-substrate interface are not primarily responsible for the observed self-polarization effect in our films. (C) 2013 AIP Publishing LL

Ferroelectric nanocomposites based on polymer ferroelectrics and graphene/oxide graphene: Computer modeling and SPFM experiments

The authors are thankful to the Russian Science Foundation (RSF grant # 16-19-10112) and to the Russian Foundation for Basic Researches (RFBR grants # 16-51-53917) for support. Prof. Xiang-Jian Meng expresses his gratitude to the National Natural Science Foundation of China (NNSFC) for support of the project: "The study on the new type of infrared detector based on ferroelectric tunnel junction"

Dynamic Behavior in Piezoresponse Force Microscopy

Frequency dependent dynamic behavior in Piezoresponse Force Microscopy (PFM) implemented on a beam-deflection atomic force microscope (AFM) is analyzed using a combination of modeling and experimental measurements. The PFM signal comprises contributions from local electrostatic forces acting on the tip, distributed forces acting on the cantilever, and three components of the electromechanical response vector. These interactions result in the bending and torsion of the cantilever, detected as vertical and lateral PFM signals. The relative magnitudes of these contributions depend on geometric parameters of the system, the stiffness and frictional forces of tip-surface junction, and operation frequencies. The dynamic signal formation mechanism in PFM is analyzed and conditions for optimal PFM imaging are formulated. The experimental approach for probing cantilever dynamics using frequency-bias spectroscopy and deconvolution of electromechanical and electrostatic contrast is implemented.Comment: 65 pages, 15 figures, high quality version available upon reques

LOCAL PIEZOELECTRICITY IN SrTiO3-BiTiO3 CERAMICS

Local piezoelectric properties of Bi-doped SrTiO3 ceramics have been investigated by piezoresponse force microscopy. The appearance of both out-of-plane and in-plane polarization components confirmed the piezoelectric nature of the obtained signal. The absence of labyrinth-like structures in observed piezoelectric contrast is not consistent with the expected existence of a relaxor ferroelectric state in this material. The close similarity of local piezoelectric properties in Bi-doped SrTiO3 with pure SrTiO3 suggests that the origin of obtained piezoresponse can be attributed to the flexoelectric phenomenon. Bi-doping leads to occurrence of oxygen vacancies and negative charge on the surface of the sample