Ferroelectricity and negative piezoelectric coefficient in orthorhombic phase pure ZrO2 thin films

A new approach for epitaxial stabilisation of ferroelectric orthorhombic (o-) ZrO2 films with negative piezoelectric coefficient in ∼ 8nm thick films grown by ion-beam sputtering is demonstrated. Films on (011)-Nb:SrTiO3 gave the oriented o-phase, as confirmed by transmission electron microscopy and electron backscatter diffraction mapping, grazing incidence x-ray diffraction and Raman spectroscopy. Scanning probe microscopy techniques and macroscopic polarization-electric field hysteresis loops show ferroelectric behavior, with saturation polarization of ∼14.3 µC/cm2, remnant polarization of ∼9.3 µC/cm2 and coercive field ∼1.2 MV/cm. In contrast to the o-films grown on (011)-Nb:SrTiO3, films grown on (001)-Nb:SrTiO3 showed mixed monoclinic (m-) and o-phases causing an inferior remnant polarization of ∼4.8 µC/cm2, over 50% lower than the one observed for the film grown on (011)-Nb:SrTiO3. Density functional theory (DFT) calculations of the SrTiO3/ZrO2 interfaces support the experimental findings of a stable polar o-phase for growth on (011) Nb:SrTiO3, and they also explain the negative piezoelectric coefficient.This work was supported by: (i) the Portuguese Foundation for Science and Technology (FCT) in the framework of the Strategic Funding Contract UIDB/04650/2020 and (ii) Project NECL - NORTE-01-0145-FEDER-022096 and Project UID/NAN/50024/2019. This work has received funding from the European Union's Horizon 2020 research and innovation programme under grant agreement No 958174 (M-ERA-NET3/0003/2021 - NanOx4EStor). This work was also developed within the scope of the project CICECO-Aveiro Institute of Materials, UIDB/50011/2020 & UIDP/50011/2020, financed by national funds through the Portuguese Foundation for Science and Technology/MCTES. It is also funded by national funds (OE), through FCT – Fundação para a Ciência e a Tecnologia, I.P., in the scope of the framework contract foreseen in the numbers 4, 5 and 6 of the article 23, of the Decree-Law 57/2016, of August 29, changed by Law 57/2017, of July 19.The calculations were carried out at the OBLIVION Supercomputer (based at the High Performance Computing Center - University of Évora) funded by the ENGAGE SKA Research Infrastructure (reference POCI-01-0145-FEDER-022217 - COMPETE 2020 and the Foundation for Science and Technology, Portugal) and by the BigData@UE project (reference ALT20-03-0246-FEDER-000033 - FEDER and the Alentejo 2020 Regional Operational Program). Oblivion resources were accessed through the advanced computing projects CPCA/A2/5649/2020 and CPCA/A2/4628/2020, funded by FCT I.P. The authors gratefully acknowledge the HPC RIVR consortium (www.hpc-rivr.si) and EuroHPC JU (eurohpc-ju.europa.eu) for funding this research by providing computing resources of the HPC system Vega at the Institute of Information Science (www.izum.si)The calculations were carried out at the OBLIVION Supercomputer (based at the High Performance Computing Center - University of Évora) funded by the ENGAGE SKA Research Infrastructure (reference POCI-01-0145-FEDER-022217 - COMPETE 2020 and the Foundation for Science and Technology, Portugal) and by the BigData@UE project (reference ALT20-03-0246-FEDER-000033 - FEDER and the Alentejo 2020 Regional Operational Program). Oblivion resources were accessed through the advanced computing projects CPCA/A2/5649/2020 and CPCA/A2/4628/2020, funded by FCT I.P. The authors gratefully acknowledge the HPC RIVR consortium (www.hpc-rivr.si) and EuroHPC JU (eurohpc-ju.europa.eu) for funding this research by providing computing resources of the HPC system Vega at the Institute of Information Science (www.izum.si

Exploring the effect of low concentration of stannum in lead-free BCT-BZT piezoelectric compositions for energy related applications

Piezoelectric, ferroelectric and electromechanical properties were studied at macroscopic and local scale level in stannum doped (Ba0.88Ca0.12)(SnxZr0.1-xTi0.9)O3 ceramics, with an objective to explore the effect of low content (0 x 0.5 at%) of the substituent (Sn) on the functional properties. The results exemplified that the substitution had an influence on the crystal lattice and microstructure that affected the dielectric, ferroelectric, and electromechanical properties. Enhancement in electrical/electromechanical properties were observed with stannum substitution. Optimal electrical properties were obtained in the composition with Sn = 0.3 at% that exhibited maximum piezoelectric constant d33 = 405 pC/N, planar electromechanical coupling factor kp ~ 0.41, and saturation polarization Ps =12.1 μC/cm2 . The same composition showed an electric-field strain response, Smax ~ 0.08% and a converse piezoelectric coefficient, 33 ∗ of ~ 525 pm/V. Local scale characterization via piezoresponse force microscopy technique revealed complex domain patterns comprising stripe-like macro-domains and featureless nanosized domains. Energy harvesting and energy storage performance were evaluated for exploring their suitability in energy applicationspublishe

Wake-up free ferroelectric rhombohedral phase in epitaxially strained ZrO2 thin films

Zirconia- and hafnia-based thin films have attracted tremendous attention in the past decade because of their unexpected ferroelectric behavior at the nanoscale, which enables the downscaling of ferroelectric devices. The present work reports an unprecedented ferroelectric rhombohedral phase of ZrO2 that can be achieved in thin films grown directly on (111)-Nb:SrTiO3 substrates by ion-beam sputtering. Structural and ferroelectric characterizations reveal (111)-oriented ZrO2 films under epitaxial compressive strain exhibiting switchable ferroelectric polarization of about 20.2 μC/cm2 with a coercive field of 1.5 MV/cm. Moreover, the time-dependent polarization reversal characteristics of Nb:SrTiO3/ZrO2/Au film capacitors exhibit typical bell-shaped curve features associated with the ferroelectric domain reversal and agree well with the nucleation limited switching (NLS) model. The polarization-electric field hysteresis loops point to an activation field comparable to the coercive field. Interestingly, the studied films show ferroelectric behavior per se, without the need to apply the wake-up cycle found in the orthorhombic phase of ZrO2. Overall, the rhombohedral ferroelectric ZrO2 films present technological advantages over the previously studied zirconia- and hafnia-based thin films and may be attractive for nanoscale ferroelectric devices.This work was supported by (i) the Portuguese Foundation for Science and Technology (FCT) in the framework of the Strategic Funding Contract UIDB/04650/2020 (ii) DSTSERB, Government of India, through Grant ECR/2017/ 00006, (iii) Project NECL - NORTE-01-0145-FEDER-022096 and Project UID/NAN/50024/2019. This work was also developed within the scope of the project CICECO-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. R.F.N., M.C.I,. and C.G. acknowledge the financial support from the Romanian Ministry of Education and Research within the project PN-III-P4-ID-PCCF2016-0047, contract 16/2018. Work at LIST was supported by the Luxembourg National Research Fund through projects PRIDE/15/10935404 “MASSENA” (S.D.) and INTER/ ANR/16/11562984 “EXPAND” (H.A. and J.I.́). The authors acknowledge the CERIC−ERIC Consortium for access to experimental facilities and financial support under proposal 20192055. The authors also thank José Santos for technical support in the Thin Film Laboratory at CF-UM-UP. The equipment of the Ural Center for Shared Use “modern nanotechnology” Ural Federal University (Reg. No. 2968) was used with the financial support of the Ministry of Science and Higher Education of the RF (Project No. 075-15-2021-677)

Narrow optical gap ferroelectric Bi2ZnTiO6 thin films deposited by RF sputtering

This work reports the deposition of single phase Bi2ZnTiO6 thin films onto Pt/Si-based substrates using the RF-sputtering method and the respective structural, morphological, optical and local ferroelectric characterization. The thin film grows in the polycrystalline form with tetragonal P4mm symmetry identified by X-ray diffraction. The lack of a spatial inversion centre was confirmed by the second harmonic generation. A narrow indirect optical gap of 1.48 eV was measured using optical diffuse reflectance. The ferroelectric domain reversal was further demonstrated through piezo-response force microscopy. This work demonstrates a practical method to fabricate the BZT perovskite phase, without resorting to high pressure and temperature conditions necessary to synthetize the bulk form, with outstanding optical and ferroelectric properties.This work was supported by national funds through the Portuguese Foundation for Science and Technology (FCT/MEC) and COMPETE 2020. when appropriate, co-financed by FEDER under the PT2020 Partnership Agreement: Grants SFRH/BPD/80663/2011 and SFRH/BPD/92896/2013; Projects IFIMUP-IN:Norte-070124-FEDER-000070; CICECO-AIM: POCI-01-0145- FEDER-007679, PTDC/FIS-NAN/0533/2012, UID/CTM/50011/2013, UID/FIS/04650/2013, CERN/FIS/NUC/0004/2015 and NECL: NORTE-01-0145-FEDER-022096 and UID/NAN/50024/2019. Foundation CAPES through the project PNPD-UFAM/Física/1671526 is also acknowledged