High ΔT Research Articles

Boosting room-temperature electrocaloric performance in B-site complex antiferroelectrics: A synergistic design approach

As an emerging eco-friendly solid-state refrigeration technology boasting high energy conversion efficiency, there is a pressing demand for ferroelectrics exhibiting significant electrocaloric effect (ECE) at room temperature (RT) for refrigeration applications. In this study, guided by phase-field simulation, we explore the potential of B-site complex Pb[Mg(1–x)ZnxW]1/2O3 (PMZW100x) antiferroelectrics (AFE) to deliver promising symmetric positive and negative ECE near ambient temperature. The first-order AFE-paraelectric (PE) phase transition occurring around 50 °C induces a substantial change in heat quantity and yields prominent ECE upon electric excitation. Maxwell characterization reveals a potential combination of positive and negative ECE, showcasing significant advantages in cooling capacity. Given the technical limitations of existing direct methods for testing under elevated electric fields, low-field ECE is validated using the heat flux approach to ensure the legitimacy of results. Direct measurements demonstrate a high positive ΔT value of 2.76 K at 52 °C and a negative ΔT of –2.91 K at 44 °C (under 140 kV cm–1), surpassing traditional PbZrO3 bulk materials. The coexistence of substantial positive and negative ΔT near RT in PMZW100x offers a new avenue for developing highly efficient solid-state cooling devices.

The Influence of Undercooling and Sector Zoning on Clinopyroxene–Melt Equilibrium and Thermobarometry

Abstract Thermobarometry provides a critical means of assessing locations of magma storage and dynamics in the lead-up to volcanic eruptions and crustal growth. A common approach is to utilise minerals that have compositions sensitive to changes in pressure and/or temperature, such as clinopyroxene, which is ubiquitous in mafic to intermediate magmas. However, clinopyroxene thermobarometry may carry significant uncertainty and require an appropriate equilibrium melt composition. In addition, the degree of magma undercooling (ΔT) affects clinopyroxene composition and zoning, with common sector zoning potentially obfuscating thermobarometry results. Here, we use a set of crystallisation experiments on a primitive trachybasalt from Mt. Etna (Italy) at ΔT = 25–233 °C, P = 400–800 MPa, H2O = 0–4 wt % and fO2 = NNO + 2, with clinopyroxene crystals defined by Al-rich zones (prisms and skeletons) and Al-poor zones (hourglass and overgrowths) to assess common equilibrium models and thermobarometric approaches. Under the studied conditions, our data suggest that the commonly applied Fe–Mg exchange (cpx-meltKdFe–Mg) is insensitive to increasing ΔT and may not be a reliable indicator of equilibrium. The combined use of DiHd (CaMgSi2O6 + CaFeSi2O6) and EnFs (Mg2Si2O6 + Fe2Si2O6) models indicate the attainment of equilibrium in both Al-rich and Al-poor zones for almost all investigated ΔT. In contrast, CaTs (CaAl2SiO6) and CaTi (CaTiAl2O6) models reveal substantial deviations from equilibrium with increasing ΔT, particularly in Al-rich zones. We postulate that this reflects slower diffusion of Al and Ti in the melt compared with Ca and Mg and recommend the concurrent application of these four models to evaluate equilibrium between clinopyroxene and melt, particularly for sector-zoned crystals. Thermobarometers calibrated with only isothermal–isobaric experiments closely reproduce experimental P–T at low ΔT, equivalent to natural phenocrysts cores and sector-zoned mantles. Models that also consider decompression experiments are most accurate at high ΔT and are therefore suitable for outermost phenocryst rims and groundmass microlites. Recent machine learning approaches reproduce P–T conditions across all ΔT conditions. Applying our experimental constraints to sector-zoned microphenocrysts and groundmass microlites erupted during the 1974 eccentric eruption at Mt. Etna, we highlight that both hourglass and prism sectors are suitable for thermobarometry, given that equilibrium is sufficiently tested for. The combination of DiHd, EnFs, CaTs and CaTi models identifies compositions closest to equilibrium with the bulk melt composition, and results in smaller differences in P–T calculated for hourglass and prism sectors compared with applying only DiHd and EnFs equilibrium models. This provides a framework to assess crystallisation conditions recorded by sector-zoned clinopyroxene crystals in mafic alkaline settings.

Evolution behavior of electrocaloric effect in BaTiO3‐based ceramics with different phase structures and phase transitions

AbstractIn this work, the evolution behavior of electrocaloric effect in BaTiO3‐based ceramics with different phase structures and phase transitions was compared. A paradigmatic system of (Ba0.85Ca0.15)(Ti1−xHfx)O3 ceramics was selected. Diffuseness exponent γ increases linearly with rising x. Electrocaloric temperature change (ΔT) shows an opposite variation, whereas temperature span (Tspan) displays the same tendency with γ changing. The degeneration of maximum polarization and polarization change rate contributes to the decrease in ΔT due to the diffusion phase transition, whereas the diffusion can lead to a large Tspan. The ceramic with a single ferroelectric or paraelectric phase shows a small ΔT but a high variation rate with elevating electric field (E), whereas a small variation rate is present in the phase‐transition region that shows a high ΔT. Besides, small electrocaloric strength (ΔT/ΔE) is obtained in the single‐phase region and increases with elevating E. A high ΔT/ΔE is present in the phase‐transition region but decreases with elevating E. When phase transition becomes diffusion, ΔT variation with E becomes obvious, whereas ΔT/ΔE dependence will decrease. These phenomena result from the difficult polarization orientation in single ferroelectric phase or weak polarization in paraelectric phase, and the easy polarization orientation in the phase‐transition region.

Enhanced room-temperature electrocaloric and pyroelectric responses around morphotropic phase boundary and energy storage performance of lead-free Ba0.85Ca0.15Hf0.10Ti0.90O3 ceramics sintered at various temperatures

The electrocaloric (EC) cooling and energy storage capabilities of Pb-free ferroelectrics are thought to be a promising technology for developing environmentally friendly refrigeration and energy storage systems. The EC performance, energy storage and pyroelectric response of sol-gel derived Ba0.85Ca0.15Hf0.10Ti0.90O3 (BCHT) ferroelectrics sintered at various temperatures are investigated here. It is thoroughly explored how sintering temperature affects the structural and electrical characteristics of BCHT ceramics. According to structural analysis by X-ray diffraction, the morphotropic phase boundary (MPB) of tetragonal and orthorhombic phases is evolved in BCHT ceramics sintered at higher temperatures of 1250 and 1350 °C. The density, grain size, and dielectric constant of BCHT ceramics increase when the sintering temperature rises from 1150 to 1350 °C. The BCHT ceramic sintered at 1250 °C exhibits the highest room temperature pyroelectric coefficient p ∼ 15.21 10−4 C/m2K and the various pyroelectric figure of merits calculated are Fi = 7.46 10−10 m/V, Fv = 0.033 m2/C, FD = 31.82 10−6 Pa−1/2, Fe = 103.44 J/m3K2, and Fe* = 24.85 10−12 m3/J respectively. At the ambient temperature, BCHT ceramic sintered at 1250 °C with MPB displayed a high EC temperature change ΔT ∼ 0.56 K and EC efficiency ΔT/ΔE ∼ 0.28 Kmm/kV under relatively low field ΔE ∼ 20 kV/cm. The highest EC temperature change ΔT ∼ 1.01 K is also observed in BCHT ceramics sintered at 1250 °C with corresponding ΔT/ΔE ∼ 0.50 Kmm/kV at 87 °C. The observed values are higher than the value reported for other lead-free materials. The maximum recoverable energy density Jrec ∼ 116.18 10−3 J/cm3 and corresponding efficiency η ∼ 71.34 % has been observed in BCHT ceramics sintered at 1250 °C. These findings indicate that BCHT ceramics offer a promising way to develop high-performance pyroelectric sensors, electrocaloric refrigeration, and energy storage materials.

Applications of polymer coatings consisting of 9,9′-(4,4′-sulfonylbis(4,1-phenylene))biscarbazole and thiophene derivatives in electrochromic devices

A carbazole derivative (9,9′-(4,4′-sulfonylbis(4,1-phenylene))biscarbazole (SpDc)) was synthesized; subsequently, P(SpDc), P(SpDc-co-TP), P(SpDc-co-MTP), P(SpDc-co-PTP), and P(SpDc-co-HTP) films were electrochemically coated on ITO/glass substrates. Electrochromic characterizations show that the P(SpDc) film is pale ochre, dark khaki, moss green, and dark olive green at 0.0, 0.8, 1.0, and 1.1 V, respectively. The square wave potential step absorptiometry of the polymeric coatings shows that the P(SpDc-co-PTP) film exhibits a high transmittance change (ΔT = 52.8%) and a moderate coloration efficiency (η = 120.8 cm2 C−1). Furthermore, dual-layer electrochromic devices (ECDs) were fabricated using P(SpDc), P(SpDc-co-TP), P(SpDc-co-MTP), P(SpDc-co-PTP), and P(SpDc-co-HTP) as anodic coatings and PProDOT-Bz2 as the cathodic coating. P(SpDc-co-TP)/PProDOT-Bz2 ECD exhibited multicolored electrochromism, a high ΔT (50.9% at 635 nm), a high η (820.5 cm2 C−1 at 635 nm), and a fast switching time (less than 0.1 s). Given the adequate electrochromic performance of the organic coatings, it can be inferred that these coatings could be used in promising organic ECD applications.

Investigation of failure mechanism of aluminum-scandium wire bond contact under active power cycle test

The failure mechanism of aluminum-scandium (Al-Sc) wire bond in comparison with pure Al wire bond under active power cycle (APC) test was investigated. To monitor the degradation of the bond quality, bond shear forces (shear force) were measured over the testing cycles at different level of temperature swing (ΔT). The results show that the Al-Sc wire bond was much more robust than the pure Al wire bond when the ΔT (Tmax) was mild. On the other hand, as the ΔT was increased, the shear force reduction in the Al-Sc wire bond became more and more remarkable. In the cross-sectional analysis of bond contact after the APC tests, a significant crack propagation was observed even for low ΔT conditions for the pure Al wire, and the crack progressed primarily on the wire side of the bond area. As for the Al-Sc wire, while the bond crack was efficiently suppressed for low ΔT conditions, a significant progress of crack was observed at high ΔT conditions, and the crack grew mainly through the Al pad side of the bond area. A detailed analysis at the bond interface after the APC test at high ΔT condition revealed three phenomena at the Al pad side of the bond area: grain coarsening, precipitation of Cu particles, and large void formation. As the material strength is compromised by these effects, the crack grew more easily through the Al pad side of the contact area, resulting in a rapid reduction of shear force at high ΔT. The bond failure mechanism obtained in this study will provide a valuable insight for the future development of high reliability power semiconductor device.

Stable viologen-based electrochromic devices: Control of Coulombic interaction using multi-functional polymeric ionic liquid membranes

Newly designed polymeric ionic liquid, poly(vinylidene fluoride-co-difluorovinylidene aminooxoethyl-1-butylimidazolium-co-vinylidene aminooxoethyl-1-butylimidazolium tetrafluoroborate) (denoted as PFI-BF 4 ), were successfully synthesized with an intention to form the stable electrospun membranes as quasi-solid-state electrolytes for the use in the electrochromic devices (ECDs). The fluorine atoms in the PFI-BF 4 membranes could restrain viologen from being quenched on the cathode. The incorporation of imidazolium entities in the PFI-BF 4 membranes could enhance the electrochemical stability and lower the charge transfer resistance at the electrolyte/cathode interface due to the suppression of viologen which are being trapped on the membranes. With an optimal molar ratio of imidazoliums to fluorines on the PFI-BF 4 membranes, the viologens would be nearly free from aggregation since the Coulombic attraction towards fluorines and the Coulombic repulsion towards imidazoliums reach equilibrium. After a systematic investigation, the PFI-BF 4 _1.5 ECD exhibited a high transmittance change (ΔT) of 73.0%, with an effective coloration efficiency ( η e ) of 460 cm 2 C -1 at 600 nm and fast response times (bleaching time of 3.9 s and coloring time of 1.7 s). Most importantly, the PFI-BF 4 _1.5 ECD retained 95.9% and 88.3% of its initial ΔT after 10,000 and 50,000 continuous switching cycles, respectively. • Newly designed polymeric ionic liquid (PFI-BF 4 ) with an intention to use in the ECD. • The fluorine atoms in the PFI-BF 4 could restrain viologen to quench on the cathode. • The imidazole entities in the PFI-BF 4 could suppress viologen on the membrane. • The PFI-BF 4 _1.5 ECD exhibited a high ΔT of 73.0% with η e of 460 cm 2 C -1 at 600 nm. • The studied ECD retained 95.9% and 88.3% of its initial ΔT after 10k and 50k cycles.

Dual-function smart windows with dynamic and fast thermal response for building energy-saving/storage

Thermochromic smart windows are considered an important element for increasing building energy efficiency. However, the phase transition of conventional devices only depends on the surrounding temperature with solar irradiation, which limits their application under different conditions. Here, a thermoelectrochromic dual response device has been designed by combining thermochromic hydroxypropyl cellulose/potassium chloride (HPC/KCl) hydrogel electrolyte and optothermal electrochromic polyaniline (PANI) films. The thermoelectrochromic device (T-ECD) exhibits electrochromic switchable colour tones (light yellow to purple), visible luminous transmittance (15.70–75.53%), and high solar modulation efficiency (60.89%) when this electrochromic switching is combined with thermochromic phenomenon arising from the electrolyte. Further, since PANI is able to store charge reversibly during the electrochromic transition, this device may also be used as a photovoltaic energy storage. Under solar irradiation, the photothermal effect of PANI films can drive the fast phase transition of HPC/KCl hydrogel. The phase transition time of T-ECD is 30 s which is much faster than 3 min of conventional TCD. In addition, a field test further demonstrates that the house model equipped with the T-ECD can reduce the indoor temperature by 13.3 °C compared with that using a traditional glass window. Thus, it is a valuable device to be used in buildings for energy-saving/storage situations. • An innovative T-ECD was designed and shows a wide range of T lum (15.70–75.53%), high ΔT sol (60.89%), low LCST (30 °C). • The T-ECD exhibited photothermal property to drive the fast phase transition (30 s). • Simulating real building-based T-ECD is 13.3 °C lower than that of using a traditional glass window.

Thermo- and electrochromic smart window derived from a viologen-tethered triazolum based poly(NIPAmn-TEG-BPV) electrolyte to enhance building energy efficiency and visual comfort

In this work, we synthesized by facilely incorporating a modified asymmetric viologen onto the triazole moiety of a phase-changing monomer [poly(NIPAmn-TEG)] via quaternization to produce dual-responsive material [poly(NIPAmn-TEG-BPV)]. However, most chromic material-based smart windows have responded to only one stimulus, but studies on dual-responsive windows are to be given more attention due to the many opportunities in terms of utility and activity that they offer. Whereas here in our work apart from being electrochromic, the material is thermochromic as well, switching from clean to opaque at when heated from 25 to 32 °C as a result of phase transformation, attaining >84.7 % optical contrast (ΔT) in the visible range (650 nm). Similar results were obtained while switching from a clear state to a purple state at an applied potential of ∼ 2.5 V which gave an optical contrast of (ΔT) >89.6 % (550 nm). A coloration speed of 8.1 s and bleaching speed of 26.1 s were attained by the poly(NIPAmn-TEG-BPV) with a coloration efficiency of 346 cm2C−1 and cyclic stability of >500 cycles. The synergistic effect of its thermochromic and electrochromic response when stimulated simultaneously, showed a transparent state to a cloudy blue state and gave high (ΔT) >91.05 % with full absorption of the entire visible solar spectrum resulting to a truly blue opaque state that is ideal for building façade requiring absolute privacy.

Heuristic Detection of the Most Vulnerable Regions in Electronic Devices for Radiation Survivability

As electronic systems become larger and more complex, detection of the most vulnerable regions (MVR) to radiation exposure becomes more difficult and time consuming. We present a heuristic approach where the mechanical and thermal aspects of devices are exploited to quickly identify MVRs. Our approach involves the topological mapping of two device conditions. The first condition identifies regions with the highest mechanical strain or density of defects and interfaces via thermal wave probing and phase analysis. The second condition identifies regions with high electrical field. It is hypothesized that the region with the highest thermal wave penetration resistance and electrical field will exhibit the highest sensitivity to incoming radiation for single events and potentially, total ionizing dose. Our approach implements a simplistic design that improves analysis time by ∼2–3 orders of magnitude over current radiation sensitivity mapping methods. The design is demonstrated on the well-studied operational amplifier LM124, which shows agreement with the literature in identifying sensitive transistors–QR1, Q9, and Q18–with relatively high phase percentile values (>70%) and ΔT percentiles (>50%), satisfying conditions for elevated radiation susceptibility. This is followed by experimental results on a static random access memory (HM-6504) and a Xilinx Artix-7 35 T system on a chip.

Electrochromic Polymers Based on 1,4-Bis((9H-carbazol-9-yl)methyl)benzene and 3,4-Ethylenedioxythiophene Derivatives as Promising Electrodes for Flexible Electrochromic Devices

A 1,4-bis((9H-carbazol-9-yl)methyl)benzene (DCB)-containing homopolymer (P(DCB)) and four DCB- and ED-derivative (3,4-ethylenedioxythiophene (EDOT) and 3,4-ethylenedioxythiophene-methanol (EDm))-containing copolymers (P(DCB-co-ED), P(2DCB-co-ED), P(DCB-co-EDm), and P(2DCB-co-EDm)) were electropolymerized on ITO-polyethylene terephthalate (PET) substrates and their electrochromic performances were studied. DCB displays a lower Eonset than that of EDOT and EDm, conjecturing that the biscarbazole-containing DCB group shows a stronger electron-donating property than that of the ED derivatives. The P(2DCB-co-ED) film presents slate grey, dark khaki, and dark olive green at 0.0, 1.0, and 1.2 V. Bleaching-to-coloring switching studies of polymers show that P(2DCB-co-EDm) shows a high ΔT (31.0% at 725 nm) in solutions. Five dual-layer flexible electrochromic devices (ECDs) based on P(DCB), P(DCB-co-ED), P(2DCB-co-ED), P(DCB-co-EDm), and P(2DCB-co-EDm) as the anodic materials and PEDOT-PSS as the cathodic material are constructed. The P(2DCB-co-ED)/PEDOT-PSS flexible ECD shows a high ΔT (40.3% at 690 nm) and long-term electrochemical cycling stability, while the P(DCB-co-EDm)/PEDOT-PSS ECD shows a high ΔT (39.1% at 640 nm) and short response time (≤1.5 s). These findings offer us a new structural insight for the valuable design of conjugated polymers in high-contrast, flexible ECDs.

Modeling daily global solar radiation using only temperature data: Past, development, and future

Accurate determination on global solar radiation (Rs) is essential in many disciplines and sectors. This study comprehensively reviewed 78 existing models and developed 4 new models (N1-1∼N1-4) for estimating daily Rs using only temperature data. The best model was then applied to forecast daily Rs using temperature data in weather forecast. All models were calibrated and tested using data collected from 105 radiation stations scattered across China. Daily data of temperature were also collected from 703 additional meteorological stations to classify diurnal temperature range (ΔT) zones in China. The results showed that China could be divided into five ΔT zones. The newly developed model N1-4 was the most accurate among all models for various ΔT zones, with values of coefficient of determination, index of agreement, mean bias error, mean absolute bias error, root mean square error, and relative root mean square error in the ranges of 0.660–0.737, 0.888–0.919, −0.023–0.100 MJ m−2 d−1, 2.691–3.195 MJ m−2 d−1, 3.725–4.231 MJ m−2 d−1, and 0.224–0.352, respectively. The generalized coefficients of the N1-4 model were also derived and further used for estimating daily Rs in areas with or without Rs data when there are only temperature data. The model N1-4 was successfully applied to predict daily Rs in varying ΔT zones with forecast temperature data for a lead time of 1–8 days. This new model is recommended for forecasting daily Rs in zones with high ΔT for a long lead time and in zones with low ΔT for a short lead time.

Electrochromic devices composed of polyaniline and tungsten trioxide thin films with succinonitrile/polyethylene glycol solid-state composite electrolyte

Electrochromic (EC) materials have various absorptivity according to their redox states. An electrochromic device (ECD) employing EC material electrodes can change its absorbance toward incident light upon switching external bias. In this study, thin films of polyaniline and tungsten trioxide are electrodeposited on tin-doped indium oxide conducting glass to fabricate EC electrodes. Solid-state ECDs composed of the electrodes and succinonitrile/polyethylene glycol (SN/PEG) composite electrolytes are constructed. Their EC properties, including transmittance modulation ability (ΔT), color-switching response time, coloration efficiency, and color cycling stability, are investigated. The appropriate operating voltage range is scrutinized by a proposed method. The solid-state Pani-WO3 ECD using a SN/PEG composite electrolyte containing 10.0 wt% PEG exhibited the fastest color-switching rate and high ΔT. The device maintained its ΔT for 4500 successive color-switching cycles without significantly decreasing.

Effect of microstructure on the thermal conductivity of thermal barrier coating deposited by chelate-flame spraying

To reveal the structure-property relationships of the microstructure and the thermal conductivities of the coatings, Er2O3 coatings were directly deposited on an aluminum alloy substrate without bond coating by chelate flame spraying (CFS). The thermal insulation capability, thermal conductivity, microstructure, porosity, and splats of each coating were studied as a function of thickness. The coating with a thickness of 300 μm exhibited a high ΔT value that was 43.1% higher than that of the 100 μm-thick coating deposited with the same spray conditions. The 100 μm-thick coating exhibited low thermal conductivity, which decreased from 4.56 Wm−1K−1 to 2.57 Wm −1K−1 in the semistable phase (500 °C and 600 °C); this was mainly due to its special microstructure, which contained more mesh splats and higher porosity (28.3%) than the 300 μm-thick coating. Moreover, the effects of the microstructure on the thermal insulation capacities of the CFS coatings were determined. The results showed that as-deposited thick coatings offered higher heat conduction in the studied temperature range (from room temperature to 600 °C) than thin coatings. To conclude, this study also provides a new test method to determine thermal conductivity and thermal insulation capacity.

Phase changing poly(ionic liquid) with electrolytic functionality for a single-layer ionogel-based smart window with multi-stimuli response

Functional materials play a crucial role in the design of smart windows that can provide a more comfortable indoor environment for people to enjoy a better lifestyle. A traditional smart window material tends to have only a single feature wherein the color change is led by solar energy input. It was known that different color tones have a significant influence on people's emotions. Herein, our group has adopted a strategy to combine the properties of an electro- and thermo-chromic in a single layer (all-in-one) ionogel. In this work, 3-chloro-N-isopropylacetamide containing thermo-responsive poly [VNIm][TFSI] based electroactive has been synthesized for multi-responsive device. Ionogel, consisting of MBV [TFSI], ferrocene, and poly [VNIm][TFSI], was utilized to construct a single layer (all-in-one) device (with and without water). The proposed ionogel based device 1 (with water) that could offer a useful response to surrounding environments by switching between opaque and transparent in the aqueous condition through a temperature change. This kind of device 1 can be utilized as an individual privacy smart windows, under specific conditions. On the other hand, the ionogel based device 2 (without water) exhibits remarkable electrochromic performance through a reversible color change between colorless to purple color once 1.8 V was applied at 25 °C (below UCST) and gave a high (ΔT) of 74.9% and a coloration efficiency (CE) of 229.03 cm2 C−1 with coloration and bleaching times of 10.2 s and 100 s, respectively, while the tone changes from purple to blue when the device 2 is above UCST (52 °C). These phenomena are caused by the synergetic effect of its electrochromic reaction and thermochromic behavior. The device 2 maintained its switching stability for >2000 cycles. This novel strategy of integrating thermo- and electrochromic materials into a single device will lead to the development of the next generation of multifunctional smart windows.

A study on quaternary mixed fluoride salts as heat storage materials

Mixed fluoride salts have shown great potential as heat storage materials. In this study, a series of these salts were prepared from NaF, KF, MgF2, and CaF2, and their physical and thermodynamic properties were systematically investigated. Upon melting, these quaternary fluoride salts formed new double salt phases, and different initial formulations resulted in different contents and compositions of the double salt phases. The five groups with the optimal formulations contained only the KCaF3 and KMgF3 double salt phases, while the two reference samples contained KCaF3, KMgF3, K2MgF4, and NaMgF3 double salt phases. The emergence of new phases decreased the latent heats of the salts. The formulation with the largest theoretical latent heat (NKMC-5) initially showed better performance; however, its high ΔT and ΔT′ values decreased its thermal cycling stability (ΔT is the difference between the melting onset and saturation point temperatures, whereas ΔT′ is the difference between the melting onset temperature and the temperature at which 90 % of the material is in the liquid phase). Microstructural analyses revealed that the structural compaction changed with different salt ratios owing to the formation of new phases and changes in the liquid content with temperature.

High optical contrast and radiant heat blocking properties of hierarchically structured electrodes for electrochromic windows

To prepare the electrochromic electrode, a hierarchical structure of ZnO nanorods (2s-ZnR) was grown via the two-step hydrothermal process and used to mitigate electron scattering and improve the optical transmittance of the electrodes. Compared to the electrode with 1s-ZnR, a 36.6% increase in ΔT% (an increase from 24.3 to 33.2) along with fast coloring and bleaching processes (time reduced by 0.4 and 0.6 s, respectively) were achieved with the 2s-ZnR structured electrode. When an optimal sp-WO3 thickness was prepared, the Hier-electrode with a double-hierarchical structure of dip-WO3/sp-WO3/2s-ZnR exhibited a high ΔT% of 50.8, compared to 41.7 and 33.8 analyzed from the Sput- and Dip-electrodes, respectively. When the voltage was switched, the Hier-electrode responded quickly, with tc of 12.7 s and tb of 3.8 s. Moreover, when the heat-irradiation time was extended from 60 to 150 s, the temperature of Hier-electrode only slightly increased by 8.15%. Clearly, the Hier-electrodes exhibit a high contrast ratio, fast response, and high radiant heat blocking capability, which has high potential for smart window applications.

Effect of laser power density on the electrochromic properties of WO3 films obtained by pulsed laser deposition

Pulsed laser deposition (PLD) was used to prepare tungsten trioxide (WO3) films on ITO substrates with a varying laser power density of 4.0–5.5 W/cm2. XPS indicated that when the laser power density decreased, the peak positions of the W 4f and O 1s orbits shifted slightly to low energy due to the difference in oxygen vacancies. As the laser power density decreased, W6+ gradually replaced the lattice position of O2−, increasing oxygen vacancies in the lattice. The transmittance modulated values (ΔT) were over 44% at 830 nm, indicating strong absorption by the WO3 thin films in the near-infrared ray. The switching time of the WO3 thin films between bleached states and coloured states decreased as the laser power density increased due to the amorphous structure, morphology, and lower oxygen deficiency at a high power density. The high ΔT and very fast switching time of tb (1.09 s) and tc (6.01 s) demonstrated the excellent electrochromic (EC) properties of the WO3 films prepared by PLD.

Electrosynthesis of Electrochromic Polymer Membranes Based on 3,6-Di(2-thienyl)carbazole and Thiophene Derivatives.

Five carbazole-containing polymeric membranes (PDTC, P(DTC-co-BTP), P(DTC-co-BTP2), P(DTC-co-TF), and P(DTC-co-TF2)) were electrodeposited on transparent conductive electrodes. P(DTC-co-BTP2) shows a high ΔT (68.4%) at 855 nm. The multichromic properties of P(DTC-co-TF2) membrane range between dark yellow, yellowish-green, gunmetal gray, and dark gray in various reduced and oxidized states. Polymer-based organic electrochromic devices are assembled using 2,2′-bithiophene- and 2-(2-thienyl)furan-based copolymers as anodic membranes, and poly(3,4-ethylenedioxythiophene)-poly(styrene sulfonic acid) (PEDOT-PSS) as the cathodic membrane. P(DTC-co-TF)/PEDOT-PSS electrochromic device (ECD) displays a high transmittance change (ΔT%) (43.4%) at 627 nm as well as a rapid switching time (less than 0.6 s) from a colored to a bleached state. Moreover, P(DTC-co-TF2)/PEDOT-PSS ECD shows satisfactory optical memory (the transmittance change is less than 2.9% in the colored state) and high coloration efficiency (512.6 cm2 C−1) at 627 nm.

Effect of Synthesis Temperature on Size, Structure, and Volume Phase Transition of Polysaccharide Microgels

High-molecular-weight polysaccharide microgels were synthesized at a range of temperatures above the polymer lower critical solution temperature (LCST) (ΔT = 0.6–18.1 °C), and ΔT was found to strongly influence the structure, dynamics, and volume phase transition temperature of the resulting particles. Static and dynamic light scattering studies and mean field theory analysis of the microgels below and above volume phase transition revealed several distinct regimes. At small ΔT, lower density, larger, and more polydisperse microgels that deswell by a factor 10 in volume were synthesized. At intermediate ΔT = 5–8 °C, the formed microgels were the smallest, densest, and most monodisperse below the transition, but exhibited deswelling only by a factor of 5 above the transition. Synthesis at high ΔT led to the formation of nonuniform microgels with small density, a high degree of polydispersity, and in some cases the apparent presence of the un-cross-linked polymer. Furthermore, the volume phase transition temperature dropped significantly as ΔT increased. This work suggests that synthesis temperature can be used to tune the size, deswelling capacity, and volume phase transition temperature of the polymeric microgels.