The aim of this work is to study the critical parameters governing the eCe (elastocaloric effect) of poly-isoprene rubber (NR and IR) in use conditions of a cooling device, i.e. under partial cyclic loading. The effect of mechanical cyclic loading parameters (pre-extension ratio, waveform and frequency) on eCe was first studied. It shows that the eCe increases when the mimimum pre-extension ratio is increased and frequency is lowered from 1Hz to 0.001Hz, as it promotes strain-induced crystallization. However, it also leads to a decrease in potential cooling power, from 7 to 0.01 MW/m3 (i.e. 8 kW/kg to 0.01 kW/kg). At intermediate frequency (f≈0.1 Hz), the comparison of square and triangular waveforms demonstrated that the former enables greater temperature variation. This is due to its holding step (at maximum extension ratio), which maximizes crystallization but also promotes stress relaxation, resulting in increased mechanical losses. Consequently, the square and triangular loadings have a COPmat of 12 and 25, with a temperature variation of 4.2K and 3.6K, respectively. Regarding the formulation, rubbers that do not have a great tendency to crystallise such as synthetic polyisoprene rubber seem to have the best COPmat, while to maximise ΔT, the best of our formulations are NR crosslinked with sulphur and having a crosslink density close to 1.5×10-4 mol/cm3, which combine large strain induced crystallisation and entropic elasticity. This material has a COPmat of about 27 and allows a ΔT≈4K, i.e.performance comparable to that of the best Shape Memory Alloys (at equivalent COPmat).

We have studied the effects of Zn and Nb substitutions on dielectric, ferroelectric, and piezoelectric properties of Ba0.87Ca0.13(Ti0.9Zr0.1)(1−x)(Zn1/3Nb2/3)xO3 ceramics. X-ray diffraction (XRD) results display that morphotropic boundary occurs from tetragonal to orthorhombic region for x = 0; 0.005; 0.01 and polymorphic phase transitions from tetragonal to orthorhombic and rhombohedral regions for x = 0.02. The evolution of the Raman spectra demonstrates the introduction of a disorder in this composition, which promotes ferroelectric relaxor behaviors. Ferroelectricity is confirmed by hysteresis investigation. A piezoelectric coefficient of d33 = 205 pC N−1 and a high planar electromechanical coupling factor of kp = 47% are reported for x = 0.1. The ceramics for x = 0.01 also depicts uniform microstructure that contributes to the important electrical properties. These results indicate that this Ba0.87Ca0.13(Ti0.9Zr0.1)(1−x)(Zn1/3Nb2/3)xO3 system with optimal composition is a promising lead-free piezoelectric material.

Despite the excellent properties of Pb(Zn1/3Nb2/3)O-3-4.5PbTiO(3) (PZN-4.5PT) single crystals, the greatest difficulty for their application on electronic devices is to make them to thin layers related to the difficulty to make them as ceramic materials. In this paper, we use the combined USAXS/SAXS/WAXS instrument at 9ID beamline at APS-ANL for in situ characterization of PZN-4.5PT inorganic perovskite nanoparticles thin films deposited on nanotextured silicon to understand the phase transitions and determine the observed microcrystals' structure. The sample was annealed from ambient to 1000 degrees C. The results revealed structure changes in the nanoparticles' thin films which could be explained by the new phase that can be assigned to the Pb-3(PO4)2-based component. The peak at 31 degrees indicates the presence of the rhombohedral phase perovskites assigned to the nanoparticles. WAXS characterization permitted to identification of many transitions during thermal annealing like dehydration or dihydroxylation of phosphorus gel -OH bonds and internal water.

Correction for ‘Enhanced electrocaloric effect, energy storage density and pyroelectric response from a domain-engineered lead-free BaTi 0.91 Sn 0.08 Zr 0.01 O 3 ferroelectric ceramic’ by Hend Kacem et al. , RSC Adv. , 2022, 12 , 30771–30784, https://doi.org/10.1039/D2RA04914G.

Alternative methods of refrigeration are critical for performance optimization and environ- mental sustainability. Prototype systems using caloric materials have shown the advantages of a high coefficient of performance (COP) and low global warming potential. Elastocaloric elastomers can meet ongoing needs, but their implementation in functional heat pumps or coolers remains challenging due to their requirement for a large deformation and low thermal conductivity. Moreover, a scalable design is required to achieve high cooling power. As a leap forward for the use of polymers in larger scale caloric devices, we developed experimental elastocaloric polymer coolers with two different geometries using natural rubber tubes. We confirmed that a suitable geometry partially compensated for the low thermal conductivity and led to performances comparable to those of other caloric devices. Several operating conditions were tested to determine the optimal temperature span, cooling power, and COP for both device geometries. Under a specific operating condition, one of the prototypes exhibited a maximum temperature span > 8 K, a maximum COP of 6, and an output cooling power of 1.5 W; this power outperforms other prototypes based on polymers or ceramics. The parallelization of rubber tubes will facilitate realistic elastocaloric polymer coolers on a larger scale.

Ferroelectric ceramics, Ba0.95Sr0.05(Ti0.95Zr0.05)1–xSnxO3 (BSTZS), with varying Sn content (x = 0 ∝ T −0.3803, EC ∝ T −0.8806, EC ∝ T −0.6010, and EC ∝ T −0.0389 for x = 0 ∝ T −0.364, Pr ∝ T −0.962, Pr ∝ T −2.170 and Pr ∝ T −4.018 for x = 0

There are potential alternatives to cold production by vapor compression. Among these possibilities, one may consider solid refrigeration based on the elastocaloric effect of materials with a low environmental footprint such as natural rubber. After a state of the art on refrigeration systems using caloric materials (barocaloric, magnetocaloric, electrocaloric, elastocaloric), this article presents the principles of cold production by regenerative systems (with heat transfer fluid) and by recovery systems (direct contact between the heat exchangers and the caloric material). Two recovery systems were designed and tested. The first system has a single actuator and operates in sequence in 2.5 times, a power of 0.2 W/g and a temperature span of 1.3 K were obtained. The second system uses two actuators, and its sequencing is in 4 times, a temperature difference of 3.5 K.

The lead-free $$\left( {{\text{Na}}_{0.5} {\text{Bi}}_{0.5} } \right)_{0.94} {\text{Ba}}_{0.06} {\text{TiO}}_{3}$$ (NBT–6BT) ceramics was fabricated at various sintering temperatures using a conventional solid-state reaction method. The effect of calcination temperature was systematically investigated on the structural properties. The XRD results show that the 850 °C is the best calcination temperature, where the NBT–6BT ceramic had the largest crystallite size with a dense sample, 96% of the theoretical value. However, the density decreased significantly with increasing the calcination temperature above 850 °C due to the secondary phase formation. On the other hand, the effect of sintering temperature was studied on the piezoelectric and ferroelectric properties evolutions. It is found that the optimal ferroelectric and piezoelectric values were obtained at 1150 °C (Pr = 27 µC/cm2, Ec = 3.89 kV/mm and d33 = 110 pC/N). According to these results, we suggest that 850 °C and 1150 °C can be considered as optimal calcination and sintering temperature in NBT–6BT ceramic, respectively.

A BaTi0.91Sn0.08Zr0.01O3 (BTSZ) ceramic was prepared by a conventional solid-state reaction method. Its structural, dielectric, ferroelectric, and pyroelectric properties were carefully studied. The Rietveld refinement was used to characterize the structural proprieties of the synthesized ceramic. The microstructure was observed by scanning electron microscopy. Phase transitions observed in the temperature dependent dielectric permittivity (epsilon(r)-T and tan delta-T) showed a transition close to room temperature, resulting in improved piezoelectric, pyroelectric and electrocaloric performance. In addition, it was found that an electric field poling process changed the character of epsilon(r)-T and tan delta-T plots. Resonance modes in the polarized state, where maximum power transmission was achieved, were observed in the impedance spectrum. The extra-slim hysteresis loops revealed a relatively low coercive field and hysteresis loss related to the diffuse phase transition, which can significantly improve energy storage efficiency up to 75% at 100 degrees C. To characterize the electrocaloric effect (ECE), indirect and direct methods based on the thermodynamic approach were used. Both methods results showed good consistency and revealed a large ECE peak evolving along the phase diagram. Furthermore, pyroelectric figures of merit (FOMs) for voltage responsivity (F-v), current responsivity (F-i), energy harvesting (F-E), new energy harvesting (F-e*) and detectivity (F-d) were calculated. Finally, thermal energy harvesting (N-D) was determined by using the Olsen cycle. The obtained maximum N-D was 233.7 kJ m(-3) when the Olsen cycle operated at 25-100 degrees C and 0-30 kV cm(-1). This study introduces not only a technique to produce a high performance ceramic for refrigeration devices, but also broadens the range of applications for BT-based lead-free ferroelectrics beyond actuators, sensors, and energy harvesting to solid-state cooling.

BaTiO3 (BT) ceramic has been prepared by the solid-state reaction method. The Rietveld refinement and the Raman spectroscopy have been employed to characterize the structural information of the BT ceramic based on the analysis of dielectric at room temperature (RT). Detailed microstructure has been observed by scanning electron microscopy. The dielectric properties of our ceramic have been investigated over wide frequency (10(2)-10(6) Hz) and temperature (-100-600 degrees C) ranges. At high temperature region (250-600 degrees C), a dielectric relaxation phenomenon has been observed. To better understand the physical mechanisms at high temperature, a macroscopic and phenomenological statistical model has been used. The calculated activation energy for relaxation and conduction was approximated to 1 eV. This suggests that relaxation in our studied sample at high temperature region is associated with the short-range hopping of ions. This is caused by oxygen vacancies in the bulk of the material. The BT ceramic demonstrated optimum electrical properties: epsilon(r) = 1105, tan delta = 0.079, T-C = 130 degrees C, epsilon(max) = 4050, P-max= 18.35 mu C/cm(2), Pr = 7.93 mu C/cm(2), E-C = 2.65 kV/cm, vertical bar Y vertical bar = 1.86*10(11) N/m(2), d(33) = 197 pC/N, kp = 14%, and Q(m) = 196. In addition, the evolution of energy storage performance with an increase in the applied electric field has been investigated. The energy storage efficiently has achieved 40 % at RT, under an electrical field of 30 kV/cm.

When natural rubber is rapidly loaded and unloaded there occurs a variation of its temperature called the elastocaloric effect. The objective of this work was to determine whether this temperature variation could be responsible for a delay in strain-induced crystallization (SIC) kinetics and stress relaxation. To this end, the SIC kinetics of cross-linked natural rubber samples with different thicknesses was studied at constant elongation after adiabatic stretching using thermal, mechanical and in-situ WAXS characterizations. The coupling of these techniques revealed that, at a fixed elongation λ (between 5 and 6), the crystallization kinetics and stress relaxation were faster in the thinner sample (with a short heat exchange time constant), thus providing evidence that heat transfer affected the SIC kinetics and should be considered when interpreting experimental results.

In this work, (Na0.5Bi0.5)(0.94)Ba0.06TiO3 ceramic doped with three lanthanides La3+, Gd3+, Ho3+ were prepared and investigated the corresponding structural, vibrational, ferroelectric and energy storage properties. The X-ray diffraction and Raman spectra reveal a pure perovskite with the coexistence of rhombohedral and tetragonal phases at room temperature for all samples. The thermal dependence of the dielectric constant shows a ferroelectric/antiferroelectric phase transition around Td, confirmed by the change in the shape of P-E hysteresis loops for all samples. We found that the optimal piezoelectric and ferroelectric properties were obtained in the ceramic doped with Ho-3+(.) Furthermore, the later sample revealed relatively remarkable features of energy storage density with temperature, reaching a maximum of 0.63 J/cm(3) around 100 degrees C. The results discussed in this work highlight the great potential of the doped NBT-6BT based lead-free ceramics.

Carbon-based electroactive polymers (EAPs) are core materials for actuator applications. Introducing conductive fillers into EAPs is considered an effective method to improve the actuating performance, due to the enhanced dielectric properties achieved. This work describes the elaboration and characterization of polyurethane (PU)/oxygen-functionalized graphene (OFG) composite films. Results revealed that for the nanocomposites, a large increase in dielectric constant was obtained without a great mechanical reinforcement, whereas there was no improvement in electromechanical performance as compared to pure polyurethane. The possible reasons for these discordant results were thus investigated with the help of multiscale studies. The importance of measuring the dielectric and mechanical properties under the same conditions as those used to drive actuators could be pointed out. Using high electric field values led to a better prediction of the electromechanical coefficient M31 for pure PU at low frequency, but did not completely explain the decreasing M31 found for the composites. The discrepancy could be due to the moderate adhesion between the polymer and the graphene nanoplatelets, but also to the competition between the increased dielectric constant and the decreased electric field seen by the polymer, induced by MWS interfacial polarization.

The Pb(Zn 1/3 Nb 2/3 )O3-4.5PbTiO 3 (PZN-4.5PT) single crystals showed very large ferroelectric and piezoelectric properties compared to traditional ferroelectric ceramics (BaTiO 3 and PZT) used presently as active material in medical imaging, detection and sonars. However, despite these excellent properties, the greatest difficulty to use PZN-4.5PT single crystals on electronic devices is to achieve them in thin layers form because of their incongruent melting property. To overcome this difficulty, we deposit them as thin layers by dispersing their nanoparticles in a gel containing a matrix that can maintain at least their bulk properties. After this size reduction at nanoscale and the annealing process following the deposition, changes and structural transformations would occur. We fabricate with success thin films by dispersing these nanoparticles in a gel. The materials show some agglomeration at the surface of the silicon substrate films (from SEM images) and non-identified hexagonal microcrystals, which could be at the origin of their excellent properties.

Nowadays, much attention is paid for developing lead-free ceramics, which can be utilized in the refrigeration domain. This communication provides a detailed description of the synthesis and characterization of a lead-free solid solution of BaTi0.91Sn0.09O3. The X-ray diffraction analysis showed that the compound exhibits a single phase of tetragonal symmetry (P4mm (99)). The average crystallite size estimated using Scherrer's technique was found to be 122 nm. The microstructure or surface morphology of the sintered sample was investigated by using scanning electron microscopy. Based on mapping image, the sensitivity and spatial resolution of the different elements in our sample were improved. Analytical and simulation data for the electrocaloric effect in our sample were reported. A good electrocaloric strength (ξ = ΔT/ΔE) of ξ = 0.171 K mm/kV near the ferroelectric-paraelectric phase transition temperature was obtained. These values are very interesting when compared to those for other materials and show the possibility of using such lead-free ceramics for refrigeration domain.

Ferroelectric materials are used in a number of applications such as sensors, transducers and health monitoring systems. The multi-physical coupling ability possessed by these materials has been established to be useful for energy harvesting applications. Lead-free BaTi0.91Sn0.09O3 ceramic has been successfully synthesized by the conventional solid-state method. The structural information of our sample has been determined by combining the Rietveld refinement using X-ray diffraction data and the Raman spectra. Based on the dielectric properties, the ferroelectric behavior of relaxor has been observed. Permittivity data have been fitted based on empirical laws describing the diffuse phase transition in the relaxor. A saturated hysteresis loop has been obtained at room temperature. The variation of remnant polarization, maximum polarization and squareness of the hysteresis loop as a function of temperature are in good accordance with phase transition deduced from dielectric properties. Based on Arrhenius' law, the link between the temperature and the back-switching polarization is estimated in order to assess the average activation energy. Our sample has shown a recovered energy density equal to 48.18 mJ/cm(3) at 110 degrees C under an electric field of 30 kV/cm, with an energy efficiency of 41%. Furthermore, the properties of pyroelectric energy harvesting according to Olsen cycle have been studied. The maximum density of pyroelectric energy harvesting per cycle for our studied ceramic has been calculated. It was found to be 210 kJ/m(3) for an electric field of 0-30 kV/cm and in temperature ranging from 20 degrees to 120 degrees C. This result leads to the ability to use our sample for energy conversion applications. (C) 2021 Elsevier B.V. All rights reserved.

Caloric materials exhibit significant entropy variations when applying appropriate excitation, pushing forward the development of solid-state cooling systems. Their development includes materials' properties optimization, with a focus on their adiabatic temperature change when driven at their limit. In order to sustain the device development, an analytical model for regenerative cooling systems is presented in this work. It consists of a caloric material driven cyclically so that it exhibits harmonic temperature variations, whereas an oscillating fluid layer is exchanging heat with the caloric material, leading to a net heat flux along one given direction. The heat transfer equation was solved analytically for harmonic excitations along the direction perpendicular to caloric material layers separated by fluid layers. In the second step, the problem was solved along an axis parallel to the layers. In order to validate the model, an experimental proof of concept was developed based on a natural rubber tube inside which water flows harmonically. The comparison between the model and experiment is given, while the model highlights the importance of the thermal boundary layer and how the geometry of the device easily compensates for the low thermal conductivity of natural rubber.