Finland, A Package Deal: Disciplinary Climate in Science Classes, Science Dispositions and Science Literacy

Finland’s educational prowess, though tempered by recent international assessments, has remained intact. This report focused on lessons that could be learned regarding secondary-level science education from the Program for International Student Assessment (PISA) 2015, science-focused assessment. That PISA iteration included not only science literacy but also students’ science dispositions (epistemology, enjoyment, interest, and self-efficacy) and the schools’ science climate measures (disciplinary climate and teaching support). Due to the hierarchical nature of the PISA data, multilevel models were employed in this Finnish study, involving 5582 students from 167 schools. Science dispositions (as outcome measures) were differently associated with teaching support and disciplinary climate (epistemology with neither; enjoyment and interest, with both). Science literacy (as an outcome measure) was associated with all four science dispositions, whether modeled with each science disposition separately or all four simultaneously. Science literacy was also associated with the disciplinary climate in science classes for all tested models. We concluded that, in the Finnish context, science dispositions and the disciplinary climate were predictive of science literacy. Furthermore, we presented evidence from the literature indicating that these conclusions may well extend to other international contexts

Pre-stressed piezoelectric actuator for micro and fine mechanical applications

Abstract In this thesis pre-stressed piezoelectric actuators for micro and fine mechanical applications have been developed. First, RAINBOW (Reduced And INternally Biased Oxide Wafer) and thick film actuators were manufactured and their electromechanical properties were characterised. In the second part, the novel pre-stressed piezoelectric actuator PRESTO (PRE-STressed electrOactive component by using a post-fired biasing layer) was developed and its electrical and electromechanical properties were measured. Commercial piezoelectric PZT 5A and PZT 5H discs were used in the RAINBOW and PRESTO actuators and PLZT paste for thick film actuators. The pre-stressing of the PRESTO actuators was based on the sintering shrinkage and different thermal expansion coefficient of the piezoelectric disc and passive material. Dielectric LTCC tape and AgPd paste were utilized as pre-stressing media and passive layer by using lamination and screen-printing, respectively. Different active and passive layer thicknesses and electrode materials were realized in order to obtain high displacements and good load bearing capability for actuators. The PRESTO actuators showed a significantly higher coercive electric field than their bulk counterparts, but a decreased remanent polarisation. The displacement as a function of load was measured under 0.3–3 N loads and electric fields up to ±0.75 MV/m. The highest displacement of 118 μm was obtained with a 250 μm thick PZT 5H actuator (Ø 25 mm) with LTCC tape (thickness ~96 μm) as the pre-stressing material. The corresponding actuator with AgPd pre-stressing material (thickness ~33 μm) produced 63 μm displacement. Additionally, PRESTO actuators were tested with a glued steel layer in a mechanical amplifier which obtained displacements up to 1.2 mm. Effective d31 coefficients of the PRESTO actuators were derived using an analysis based on unimorph model and measured displacement data. The actuators exhibited significantly enhanced effective d31 coefficients (d31eff = -690 pm/V and d31eff = -994 pm/V for PZT 5A and 5H, respectively) comparable to the RAINBOW actuators. Mass-producible PRESTO actuators with high displacement, moderate load bearing capabilities and integration possibilities can be utilised in various micro and fine mechanical devices e.g. dosing devices, electromechanical locks, regulators, positioners vibrators, speakers, adjusters, pumps, valves, relays, dispensers, micromanipulators, etc

Piezoelectric flexible LCP–PZT composites for sensor applications at elevated temperatures

Abstract In this paper fabrication of piezoelectric ceramic–polymer composites is demonstrated via filament extrusion enabling cost-efficient large-scale production of highly bendable pressure sensors feasible for elevated temperatures. These composites are fabricated by utilizing environmentally resistant and stable liquid crystal polymer matrix with addition of lead zirconate titanate at loading levels of 30 vol%. These composites, of approximately 0.99 mm thick and length of  > 50 cm, achieved excellent bendability with minimum bending radius of ~ 6.6 cm. The maximum piezoelectric coefficients d₃₃ and g₃₃ of the composites were > 14 pC/N and > 108 mVm/N at pressure < 10 kPa. In all cases, the piezoelectric charge coefficient (d₃₃) of the composites decreased as a function of pressure. Also, piezoelectric coefficient (d₃₃) further decreased in the case of increased frequency press-release cycle sand pre-stress levels by approximately 37–50%. However, the obtained results provide tools for fabricating novel piezoelectric sensors in highly efficient way for environments with elevated temperatures

Piezoelectric energy harvesting from rotational motion to power industrial maintenance sensors

Abstract In industry, forecasting machinery failures could save significant time and money if any maintenance breaks are predictable. The aim of this work was to develop an energy harvesting system which could, in theory, power condition monitoring sensors in heavy machinery. In this study, piezoelectric-cantilever-type energy harvesters were attached to a motor and spun around with different rotational speeds. A mass was placed on the tip of the cantilevers, which were mounted pointing inward toward the center axis of the motor. Pointing a cantilever tip inward and increasing the distance from the center axis of the motor decreased the natural resonance frequency significantly and thus enabled higher harvested energy levels with lower rotational frequencies. Motion of the cantilever was also controlled by altering the movement space of the tip mass. This created another possibility to control the cantilever dynamics and prevent overstressing of the piezoelectric material. Restricting the movement of the tip mass can also be used to harvest energy over a wider frequency range and prevent the harvester from getting trapped into a stagnant position. The highest calculated raw power of 579.2 µW at 7.4 Hz rotational frequency was measured from a cantilever with outer dimensions of 25 mm × 100 mm. Results suggest that an energy harvesting system with multiple cantilevers could be designed to replace batteries in condition sensors monitoring revolving machinery

All-around universal and photoelastic self-healing elastomer with high toughness and resilience

Abstract Ultimately soft electronics seek affordable and high mechanical performance universal self-healing materials that can autonomously heal in harsh environments within short times scales. As of now, such features are not found in a single material. Herein, interpenetrated elastomer network with bimodal chain length distribution showing rapid autonomous healing in universal conditions (<7200 s) with high efficiency (up to 97.6 ± 4.8%) is reported. The bimodal elastomer displays strain-induced photoelastic effect and reinforcement which is responsible for its remarkable mechanical robustness (≈5.5 MPa stress at break and toughness ≈30 MJ m−3). The entropy-driven elasticity allows an unprecedented shape recovery efficiency (100%) even after fracturing and 100% resiliency up to its stretching limit (≈2000% strain). The elastomers can be mechanically conditioned leading to a state where they recover their shape extremely quickly after removal of stress (nearly order of magnitude faster than pristine elastomers). As a proof of concept, universal self-healing mechanochromic strain sensor is developed capable of operating in various environmental conditions and of changing its photonic band gap under mechanical stress

Hybrid, multi-source, and integrated energy harvesters

Abstract Energy harvesting is one of the most rapidly growing of the emerging technologies. This field has arrived at the hybrid and multi-source era, where hybrid structures and novel materials are able to boost the energy conversion efficiency and/or make the harvesters capable of benefitting from multiple energy sources simultaneously. Such hybrid and multi-source energy harvesters have not frequently been reviewed in the past, potentially because of the small number of publications compared to that of their single-source and individual counterparts. However, as their number is becoming larger, it is now necessary to give sufficient and frequent reviews of developments in the field. Furthermore, an increasing number of developed energy harvesters are moving out of the laboratory into industrial markets. In practice, energy harvesters need to be integrated with energy storage and/or end users such as sensors and wireless sensor networks. Therefore, the harvester-storage and harvester-sensor integration systems also need to be reviewed frequently. This mini review includes works reported in the first half of 2018 and provides a timely update to the published review. It focuses on the above-mentioned hybrid and multi-source energy harvesters as well as on integrated harvesters, energy storage systems and end users (e.g., sensors), including CMOS (complementary metal-oxide-semiconductor) technology-based harvesters and systems

The impact of lanthanum doping on the microstructure and colossal permittivity in BaxSr(1-x)TiO3

Abstract In this work BaSrTiO3 with three different Ba/Sr (45/55, 55/45 and 65/35) ratios and lanthanum doping concentrations of 0, 0.2, 0.4 and 0.6 ​mol.% were studied. Samples were fabricated through the mixed oxide route. The microstructures were analyzed and the phases of the compositions were defined by XRD. The increase in lanthanum doping had a pronounced decreasing effect on the grain size. The temperature dependent dielectric characteristics were measured between 0.1 and 1000 ​kHz in the temperature range of -68 – 150 ​°C. Colossal permittivity was found in all doped samples with a Ba/Sr ratio of 65/35 from which the 0.6 ​mol. % doping level of lanthanum showed the most promising characteristics with relative permittivity >48,000 and a dielectric loss ≤0.06 over the whole temperature range below 1 ​kHz. It was found that the relaxation of the colossal permittivity effect exhibited a frequency shift at the Curie temperature

The effect of titanium excess and deficiency on the microstructure and dielectric properties of lanthanum doped Ba0.55Sr0.45TiO3 with colossal permittivity

Abstract The temperature dependent dielectric properties of (Ba0.54875Sr0.44875La0.0025)Ti(1+x)O3 with both an excess and a deficiency of 0.25 mol.% TiO2 were investigated. The samples were prepared by the mixed oxide method and sintered in a conventional oven at temperatures ranging from 1400 °C to 1475 °C. The cubic perovskite structure was confirmed with XRD at room temperature. The sample with an excess of 0.25 mol.% Ti exhibited reduced grain growth while abnormal grain growth was observed for samples without Ti modification. Samples exhibited colossal permittivity for all modified compositions. With a 0.25 mol.% deficiency of Ti a permittivity over 65,000 and a tan δ under 0.05 were measured over a temperature range of −68 °C to 150 °C and a frequency range between 50 kHz and 1 MHz. This paper shows that by fine tuning the composition, materials with new, exciting and widely adjustable dielectric properties can be achieved

A simulation model for narrow band gap ferroelectric materials

Abstract Various ferroelectric simulation models have been developed in recent decades in order to study the mechanisms and predict the behaviors of ferroelectrics by simulating their hysteresis loops. Conventional ferroelectrics have wide optical band gaps (>2.7 eV), making them difficult to respond to visible light. Although their ferroelectricity can be affected by higher‐energy radiation like ultraviolet, little attention is paid to the development of their models incorporating light‐dependent factors. However, in recent years, narrow band gap (<5 eV) ferroelectrics have been discovered and are increasingly researched. These special ferroelectrics effectively absorb visible light and hence exhibit strongly light‐dependent ferroelectricity, triggering potentially a broad range of applications. Therefore, there is a need to develop a model for these ferroelectrics in order to predict their behavior under visible light. Such a model is also needed to improve the understanding of the interaction mechanisms between light and domains. In this paper, a ferroelectric simulation model based on the Jiles–Atherton theory considering light dependence is developed for the first time, and its accuracy is validated by experiments. The model shows an average error of 7.5% on polarization values compared to experimental results and thus can be employed to reliably predict photo‐induced ferroelectricity

Ferroelectric oxides for solar energy conversion, multi-source energy harvesting/sensing, and opto-ferroelectric applications

Abstract Photoferroelectrics belong to a unique material family that exhibits both photovoltaic and ferroelectric effects simultaneously. The photovoltaic effect is the only known direct method of converting light into electricity and is the basis of solar cells. The ferroelectric effect can induce piezoelectric and pyroelectric effects, which are the working principles of widely used kinetic and thermal sensors, transducers, actuators, and energy harvesters. For a long time, photoferroelectric research was restricted to theoretical investigations only because of either the wide band gap (Eg), which is not able to effectively absorb visible light, or to the weak ferroelectricity caused by a narrow Eg. Recent scientific breakthroughs, however, have opened doors for the development of practical applications. In this article, emerging concepts of creating balanced photovoltaic and ferroelectric properties for photoferroelectrics, as well as those of novel applications in future devices, are presented