Lead free piezoelectric ceramics for sonar applications and non destructive control

Cette étude est focalisée sur l’élaboration du titanate de baryum dopé au calcium et au zirconium (BCTZ), de formule Ba₀∙₈₅Ca ₀∙₁₅Ti₀∙₉₀Zr₀∙₁₀O₃, par voie solide, le but étant de mettre au point un protocole de synthèse et de frittage optimisé et répétable de ce matériau piézoélectrique sans plomb. La variation de la composition a de plus été investiguée dans le but de trouver le meilleur compromis entre température de Curie et propriétés électriques. Il a été mis en évidence l’augmentation de la température de Curie au détriment des propriétés électriques par la diminution de la quantité de zirconium. Une limite de solubilité du calcium dans la maille BCTZ a aussi été observée pour des quantités de calcium de l’ordre de 20 %at. La voie solide étant un procédé chronophage et énergivore, les micro-ondes ont donc été testées comme technique de chauffage pour le frittage. Des échantillons présentant des caractéristiques électriques, comme la constante piézoélectrique inverse (d₃₃*), supérieures à celles mesurées par voie conventionnelle ont ainsi été obtenus, et ceci en réduisant de manière drastique le temps du processus de frittage. Le chauffage micro-ondes a aussi été employé à la fois pour la synthèse et le frittage, ce qui a permis d’obtenir un matériau dense à 88 % en 1 heures 30 minutes et présentant une piézoélectricité de l’ordre de 50 pC/N.In this work barium titanate doped with calcium and zirconium (BCTZ), with the composition Ba₀⋅₈₅Ca₀⋅₁₅Ti₀⋅₉₀Zr₀⋅₁₀O₃, was synthesized by solid-state route. The aim of this work was to elaborate an optimized and reproducible synthesis and sintering procedure. Besides, the composition was slightly varied to find the best compromise between the Curie temperature and the electrical properties. A decrease of the zirconium amount in this material led to an improvement of the Curie temperature associated to a decrease of the electrical properties. A solubility limit of 20 %at for calcium in BCTZ was demonstrated. Solid-state route coupled with conventional sintering proved to be an efficient process to obtain BCTZ samples with good properties but it is an energy and time-consuming process. By using microwave heating, the sintering step duration could be drastically reduced. Higher converse piezoelectric constant (d₃₃*) was measured for samples obtained by this fast sintering method. Microwave heating was also tested both to synthesize and to sinter BCTZ. Samples with a 88 % relative density and a d₃₃ piezoelectric constant of 50 pC/N were obtained in only 90 minutes

Nouvelles céramiques piézoélectriques sans plomb pour des applications sonar ou de contrôle non destructif

In this work barium titanate doped with calcium and zirconium (BCTZ), with the composition Ba₀⋅₈₅Ca₀⋅₁₅Ti₀⋅₉₀Zr₀⋅₁₀O₃, was synthesized by solid-state route. The aim of this work was to elaborate an optimized and reproducible synthesis and sintering procedure. Besides, the composition was slightly varied to find the best compromise between the Curie temperature and the electrical properties. A decrease of the zirconium amount in this material led to an improvement of the Curie temperature associated to a decrease of the electrical properties. A solubility limit of 20 %at for calcium in BCTZ was demonstrated. Solid-state route coupled with conventional sintering proved to be an efficient process to obtain BCTZ samples with good properties but it is an energy and time-consuming process. By using microwave heating, the sintering step duration could be drastically reduced. Higher converse piezoelectric constant (d₃₃*) was measured for samples obtained by this fast sintering method. Microwave heating was also tested both to synthesize and to sinter BCTZ. Samples with a 88 % relative density and a d₃₃ piezoelectric constant of 50 pC/N were obtained in only 90 minutes.Cette étude est focalisée sur l’élaboration du titanate de baryum dopé au calcium et au zirconium (BCTZ), de formule Ba₀∙₈₅Ca ₀∙₁₅Ti₀∙₉₀Zr₀∙₁₀O₃, par voie solide, le but étant de mettre au point un protocole de synthèse et de frittage optimisé et répétable de ce matériau piézoélectrique sans plomb. La variation de la composition a de plus été investiguée dans le but de trouver le meilleur compromis entre température de Curie et propriétés électriques. Il a été mis en évidence l’augmentation de la température de Curie au détriment des propriétés électriques par la diminution de la quantité de zirconium. Une limite de solubilité du calcium dans la maille BCTZ a aussi été observée pour des quantités de calcium de l’ordre de 20 %at. La voie solide étant un procédé chronophage et énergivore, les micro-ondes ont donc été testées comme technique de chauffage pour le frittage. Des échantillons présentant des caractéristiques électriques, comme la constante piézoélectrique inverse (d₃₃*), supérieures à celles mesurées par voie conventionnelle ont ainsi été obtenus, et ceci en réduisant de manière drastique le temps du processus de frittage. Le chauffage micro-ondes a aussi été employé à la fois pour la synthèse et le frittage, ce qui a permis d’obtenir un matériau dense à 88 % en 1 heures 30 minutes et présentant une piézoélectricité de l’ordre de 50 pC/N

Influence of microwave sintering on electrical properties of BCTZ lead free piezoelectric ceramics

International audienceBarium titanate doped with calcium and zirconium (BCTZ) could be used at low temperature to replace lead based piezoelectric ceramics (PZT). The classical way to obtain BCTZ is the solid-state route coupled with conventional sintering, but this step is time-consuming. To reduce the duration of this process, microwave heating was used for sintering. It is a fast sintering method and the heating rate was around 200 °C/min in this study. Slightly better electrical properties with finer microstructures (d33* = 706 pm/V, grain size about 42.1 ± 14.2 μm) were obtained for samples sintered by microwave heating during 50 min compared to the conventional sintering (d33* = 622 pm/V, 22.6 ± 4.4 μm). The main result of this study is that by using microwave heating, the sintering step duration (including heating, dwell time and cooling) was drastically reduced: 1.5 h for microwave sintering against 12.5 h for conventional sintering

Influence of microwave sintering on electrical properties of BCTZ lead free piezoelectric ceramics

International audienceBarium titanate doped with calcium and zirconium (BCTZ) could be used at low temperature to replace lead based piezoelectric ceramics (PZT). The classical way to obtain BCTZ is the solid-state route coupled with conventional sintering, but this step is time-consuming. To reduce the duration of this process, microwave heating was used for sintering. It is a fast sintering method and the heating rate was around 200 °C/min in this study. Slightly better electrical properties with finer microstructures (d33* = 706 pm/V, grain size about 42.1 ± 14.2 μm) were obtained for samples sintered by microwave heating during 50 min compared to the conventional sintering (d33* = 622 pm/V, 22.6 ± 4.4 μm). The main result of this study is that by using microwave heating, the sintering step duration (including heating, dwell time and cooling) was drastically reduced: 1.5 h for microwave sintering against 12.5 h for conventional sintering

Teaching and learning modalities for continuing professional development in the long-term care: A rapid synthesis review

Aim: To describe the various teaching and learning modalities for the delivery of Continuing Professional Development activities for health care professionals in the long-term care sector.Background: Continuing Professional Development is a key activity that organisations undertake to achieve effective workforce planning, recruitment, retention and upskilling strategies in long-term care settings. During the Covid-19 pandemic there was a rapid move to online modalities of Continuous Professional Development, but there is a paucity of evidence in relation to their effectiveness compared with face-to-face, or in-class learning.Design: A rapid synthesis review.Methods: MEDLINE, CINAHL and HEALTH BUSINESS ELITE databases were used to identify relevant articles that were published between 2016 and 2022. Original studies of any design investigating Continuing Professional Development activities, with or without a comparison between interventions or activities were included. The Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) was followed. The Kirkpatrick model was adopted as a globally recognised method for evaluating training programmes. Results: After a full text analysis, 34 papers were included in the review. Face to face was the most common method of delivery followed by online, while blended (a mix of face-to-face and online delivery) was the least common method used. The teaching modalities were not associated with specific learning contents, but were used for a range of content. Most studies obtained positive outcomes following implementation of the educational interventions. Kirkpatrick Level 4 (results) was the most commonly measured outcome.Conclusions: While blended learning was the least common method of delivery, it was found to be more beneficial for learners than face-to-face or online exclusively. There are now new spaces to learn and new technologies that allow us to 'reimagine' where, when and how we teach. This requires Continuing Professional Development providers to design and tailor their courses according to health professionals' learning needs and the clinical contexts where they work. We recommend that Continuing Professional Development providers involve employers when designing teaching and learning activities for Long Term Care workers, to decide which modalities enable effective knowledge translation

Microwave sintering: Improvement of the electrical properties of barium titanite doped with calcium and zirconia

International audienc