A non-standard shear resonator for the matrix characterization of piezoceramics and its validation study by finite element analysis

Standard shear samples used for piezoceramic characterization lead to underestimation of the piezoelectric shear coefficients due to its dynamical clamping at resonance. This work presents the application of Alemany et al.´s automatic iterative method to the resonance of a non-Standard shear sample, in order to determine the related complex parameters of piezoceramics, thus including losses, from impedance measurements. The matrix of dielectric, elastic and piezoelectric complex parameters that fully characterize a piezoceramic, a 6mm symmetry material, can be obtained from such shear data combined with the application of the method to three other electromechanical resonances, namely: the length extensional mode of long rods or rectangular bars, length poled; the thickness extensional mode of a thin plate or disk, thickness poled, and the radial mode of a thin disk, thickness poled. Shear results are here obtained for non-Standard samples of a commercial Navy type II piezoceramic, solving the underestimation of the coefficients in the Standard shear sample and allowing the improvement of the previously reported characteristic matrix from Standard samples. Three-dimensional Finite Element Analysis (FEA) modelling of the resonances of the three material samples used in the matrix characterization was here accomplished using the improved matrix of dielectric elastic and piezoelectric material coefficients including all losses. The comparison of the experimental resonance spectra of this piezoceramic samples and the FEA results obtained for the elastically, dielectrically and piezoelectrically homogeneous items modelled is here presented and discussed.Peer reviewe

Anelastic deformation of Pb(Zr,Ti)O3 thin films by non-180° ferroelectric domain wall movements during nanoindentation

3 pages, 3 figures.Lead zirconate titanate Pb(Zr,Ti)O3 ferroelectric thin films show significant anelastic deformation when indented with spherical tipped indenters. Experiments on films with different Zr/Ti ratio and a mixed [001,100] preferred crystallographic orientation have shown that there is a good agreement between the anelastic deformation and the maximum strain achievable by non-180° domain wall movement. An expected increase of the indentation stiffness of the films also accompanies the anelastic deformation because of the single crystal elastic anisotropy. All these observations seem to indicate that non-180° ferroelectric domain wall movements occur under indentation stresses and cause anelasticity. Stresses for maximum anelastic deformation are compared with those for recently reported stress-induced depolarization.Peer reviewe

Point defect engineering of high temperature piezoelectric BiScO3-PbTiO3 for enhanced voltage response

BiScO-PbTiO is the most promising system among high sensitivity piezoelectric BiMO-PbTiO perovskite solid solutions with high Curie temperature, which are under extensive investigation for expanding the operation temperature of state of the art Pb(Zr,Ti)O (PZT) up to 400 °C. The viability of these alternative materials requires the development of specific point defect engineering that allow a range of piezoelectric ceramics comparable to commercial PZTs to be obtained, optimized for the different applications. A distinctive feature of BiMO-PbTiO systems is the simultaneous presence of both Bi and Pb at the A-site of the perovskite. This enables the possibility of introducing charged point defects without incorporating new chemical species, just by defining an A-site non–stoichiometry. In this work, we present a comprehensive study of the effects of Bi substitution for Pb, along with the formulation of Pb vacancies for charge compensation. Results indicate an overall lattice stiffening that yields reduced polarizability and compliance, and dominates over a limited enhancement of the ferroelectric domain wall dynamics, so as a largely enhanced voltage response is obtained. Specifically, BiScO-PbTiO with the A-site non-stoichiometry is shown to be very suitable as the piezoelectric component of magnetoelectric composites for magnetic field sensing.Funded by Spanish MINECO through the MAT2014-58816-R and MAT2011-23709 projects. Technical supports by Ms. I. Martínez and Ms. M. M. Antón are also acknowledged

Point defect engineering of high temperature piezoelectric BiScO3-PbTiO3 for high power operation

[EN] BiScO3-PbTiO3 is used as a model system of BiMO3-PbTiO3 perovskite solid solutions with enhanced electromechanical response at ferroelectric morphotropic phase boundaries, and high Curie temperature to demonstrate specific point defect engineering for high power operation. The objective is to obtain a range of piezoelectric ceramics comparable to hard Pb(Zr,Ti)O3 materials, optimized for the different applications. In this work, a comprehensive study of Mn substitution for Sc is provided. Care is taken to isolate the effects of the point defects from those of concomitant structural and microstructural changes that have been previously described after MnO2 addition. Results strongly suggest that Mn substitution results in the formation of (MnSc'-VO••) dipolar complexes that effectively clamp domain walls. This is the same mechanism responsible of hardening in Pb(Zr,Ti)O3. Indeed, Bi0.36Pb0.64Sc0.36-x MnxTi0.64O3 with x=0.02 is shown to be a high sensitivity piezoelectric with strongly reduced losses, suitable for high power operation between 200 and 400 ºC.Funded by Spanish MINECO through the MAT2014-58816-R and MAT2011-23709 projects. Technical supports by Ms. I. Martínez and Ms. M. M. Antón are also acknowledged.Peer Reviewe

Mechanosynthesis and Multiferroic Properties of the BiFeO3-BiMnO3-PbTiO3 Ternary System along its Morphotropic Phase Boundary

International audienceA highly topical set of materials are those ABO3 perovskite oxides, in which multiferroicity is chemically engineered by placing ferroelectrically and magnetically active cations in A-and B-site, respectively. This is the case of the BiFeO3 and BiMnO3 perovskites, and also of the solid solutions they form with PbTiO3. Interest in these binary systems is fostered by the presence of distinctive morphotropic phase boundaries (MPBs); multiferroic in the case of BiFeO3-PbTiO3, for which a high magnetoelectric response has been anticipated. Here, new compositions belonging to the ternary system BiFeO3-BiMnO3-PbTiO3, and specifically along the line that joins the former MPBs, have been prepared by mechanosynthesis to accomplish a thorough analysis of their multiferroic nature. Nanocrystalline powders with perovskite-type structure were obtained in the entire range of compositions, which all exhibited polymorphic phase coexistence allowing a line of MPBs to be established. The variation of the perovskite structural characteristics along this line has been defined, and correlated with those of the magnetic and electrical properties. A set of novel and promising multiferroic materials has been found for BiFeO3 rich compositions

Macroscopic ferroelectricity and piezoelectricity in nanostructured BiScO3–PbTiO3 ceramics

3 pages, 4 figures.-- PACS: 77.80.Bh; 73.61.Ng; 77.84.Dy; 77.80.Fm; 81.20.EvWe have studied the macroscopic electrical properties of highly dense, nanostructured ceramics of BiScO3–PbTiO3 with high Curie temperature and piezoelectric activity. Materials were processed by spark plasma sintering of nanocrystalline powder obtained by mechanosynthesis. Results indicate that the nanostructured material still presents the ferroelectric transition above 700 K. Ferroelectric switching is unambiguously demonstrated. Furthermore, ceramic disks were poled and their radial piezoelectric resonance was excited, which has not been achieved in nanostructured BaTiO3 ceramics.Funded by MEC (Spain) through the MAT2007-61884 and MAT2008-02003/NAN projects. H.A. and T.H. thank the financial support by MEC (JdC Programme) and MAEAECI, respectively. Collaboration between ICMM and CEMES is framed within the ESF COST Action 539 ELENA.Peer reviewe

Multiferroism and enhancement of material properties across the morphotropic phase boundary of BiFeO3-PbTiO3

Strong phase-change magnetoelectric responses have been anticipated by a first-principles investigation of phases in the perovskite BiFeO 3-BiCoO3 solid solution, specifically at the morphotropic phase boundary (MPB) between the multiferroic rhombohedral and tetragonal polymorphs. This might be a general property of multiferroic MPBs and a novel promising approach for room temperature magnetoelectricity, which requires the identification of suitable material systems. We present here a comprehensive description of the electrical and electromechanical properties across one such system; the perovskite BiFeO3-PbTiO3 solid solution. All the temperature dependence of dielectric permittivity, ferroelectric hysteresis loops, and piezoelectric coefficients have been obtained, and are discussed in relation to the previously reported perovskite structural evolution. Results show ceramic materials to be very promising for ferroelectric random access memories (remnant polarization as high as 63 μC cm-2 with a comparatively low coercive field of 4.5 kV mm-1 for MPB compositions) and high temperature electromechanical transduction (crystal piezoelectric coefficient of 87 pC N-1 with a Curie temperature above 873 K). Moreover, the occurrence of phase changes between the monoclinic and tetragonal polymorphs under high electric fields is indicated, while the canted antiferromagnetic character of the phases involved is corroborated. © 2014 AIP Publishing LLC.Funded by MINECO (Spain) through the MAT2011-23709 project. Dr. H. Amorín thanks financial support by MICINN Ramón y Cajal Programme (RYC-2008-03247). Ms. C. Correas and Ms. C. M. Fernández-Posada also thank the specific financial support of FPI Programme (BES-2008-005409 and BES-2012-053017, respectively).Peer Reviewe

Fine-grained high-performance Ba0.85Ca0.15 Zr0.1Ti0.9O3 piezoceramics obtained by current-controlled flash sintering of nanopowders

Due to environmental concerns, extensive research has been carried out to develop high-performance lead-free piezoceramics capable of replacing commercial lead-based materials. The lead-free (Ba0.7Ca0.3)TiO3 -Ba(Zr0.2Ti0.8)O3 system has emerged as a candidate for room temperature transducer applications because a high piezoelectric charge coefficient is achieved in this system for compositions at the morphotropic phase boundary. However, conventional ceramic processing of these eco-friendly piezoceramics demands high energy consumption because long-lasting, high-temperature heat treatments are needed, which often lead to microstructural degradation that compromises the material reliability. Field-assisted flash sintering has started to be explored since the application of an adequate electric field was shown to significantly reduce the sintering time and temperature, thereby controlling grain growth. In this work, Ba0.85Ca0.15Zr0.1Ti0.9O3 ceramics are obtained by current-controlled flash sintering of mechanosynthesized nanopowders. Exhaustive control of the sintering parameters allows tailoring of the microstructure, which allows dense fine-grained flash-sintered ceramics exhibiting a high electric field-induced strain response to be obtained.This work was supported by the Agencia Estatal de Investigación (AEI), Spain, projects PGC2018-099158-B-I00 and PID2021–122708OB-C33. S. L-B. thanks Agència de Gestió d′Ajuts Universitaris i de Recerca (AGAUR), Catalonia, Spain, for the FI-SDUR contract (2020 FISDU 00489). The authors acknowledge the ESRF (The European Synchrotron) for provision of synchrotron radiation facilities, and we would like to thank the BM25 (SpLine) staff for assistance in using the beamline.Peer ReviewedPostprint (published version

Origin of discrepancy between electrical and mechanical anomalies in lead-free (K,Na)NbO3 -based ceramics

[EN] Ferroelectric polymorphic phase coexistence, associated with either the presence of a morphotropic phase boundary or a temperature-driven polymorphic phase transition, is currently acknowledged as the key to high piezoelectric activity and is searched when new perovskite materials are developed, like lead-free alternatives to state-of-the-art Pb(Zr,Ti)O3. This requires characterization tools that allow phase coexistence and transitions to be readily identified, among which measurements of the temperature dependences of Young's modulus and mechanical losses by dynamical mechanical analysis stand out as a powerful technique to complement standard electrical characterizations. We report here the application of this technique to (K1-xNax)NbO3-based materials, which are under extensive investigation as environmentally friendly high sensitivity piezoelectrics. The elastic anomalies associated with the different phase transitions are identified and are shown to be distinctively shifted in relation to the dielectric ones. The origin of this discrepancy is discussed with the help of temperature-dependent Raman spectroscopy and is proposed to be a characteristic of diffuse phase transitions.The authors would like to thank CAPES and the Sâo Paulo Research Foundation (FAPESP), Grants No. 2012/08457-7 and No. 2013/00134-7, for the financial support. M.A. also acknowledges funding from MINECO through the MAT2014-58816-R Project.Peer Reviewe

High-sensitivity piezoelectric perovskites for magnetoelectric composites

© 2015 National Institute for Materials Science. A highly topical set of perovskite oxides are high-sensitivity piezoelectric ones, among which Pb(Zr,Ti)O3 at the morphotropic phase boundary (MPB) between ferroelectric rhombohedral and tetragonal polymorphic phases is reckoned a case study. Piezoelectric ceramics are used in a wide range of mature, electromechanical transduction technologies like piezoelectric sensors, actuators and ultrasound generation, to name only a few examples, and more recently for demonstrating novel applications like magnetoelectric composites. In this case, piezoelectric perovskites are combined with magnetostrictive materials to provide magnetoelectricity as a product property of the piezoelectricity and piezomagnetism of the component phases. Interfaces play a key issue, for they control the mechanical coupling between the piezoresponsive phases. We present here main results of our investigation on the suitability of the high sensitivity MPB piezoelectric perovskite BiScO3-PbTiO3 in combination with ferrimagnetic spinel oxides for magnetoelectric composites. Emphasis has been put on the processing at low temperature to control reactions and interdiffusion between the two oxides. The role of the grain size effects is extensively addressed.This work has been funded by the Spanish MINECO through projects MAT2011-23709 and AIB2010PT-00332. Collaboration between ICMM and CEMES is framed within the COST Action MP0904. Serviciencia S L (Spain) participation in the design and built-up of a novel magnetoelectric measurement system is acknowledged. HA thanks the Ramón y Cajal Programme for financial support.Peer Reviewe