Temperature-induced Phase Changes Research Articles

Study on the atomic scale deformation mechanism of the h-BN coating nickel matrix composites

In this paper, molecular dynamics (MD) simulations are applied to study the contact mechanical behavior of hexagonal boron nitride (h-BN) coating/Ni matrix composites during nanoindentation, revealing the material deformation mechanism. A systematic study is carried out on the load-depth curve, temperature response curve, defect morphology, and dislocation density in indentation. The results show that the presence of h-BN coating increases the actual loading area of the matrix, effectively reduces the contact stress between the tip of the indenter and the specimen, and also induces the generation of high-density Shockley dislocations, which increases the dislocation entanglement and leads to the localized hardening of the composites, thus reducing the matrix damage. During the loading process, the temperature of the specimen before the destruction of the h-BN coating is significantly lower than that after the destruction, indicating that the coating tends to block the transfer of temperature to the interior of the specimen, preventing the occurrence of temperature-induced tissue phase changes inside the specimen, and providing good protection for the interior of the specimen.

High temperature evolution of a confined silicon layer

The temperature-induced phase and morphology changes of a thin layer sandwiched between two substrates which it partially wets are investigated using transmission electron microscopy, scanning electron microscopy, and x-ray scattering techniques. For this, SiC wafers were bonded with Si layers of various thicknesses and annealed at temperatures below and above the Si melting point. Below the melting point of Si, solid-state dewetting occurs. It starts with the heterogeneous nucleation of pits at the Si/SiC interfaces and progresses to their partial transformation into voids crossing the whole film. The further growth of voids is accompanied with an increase in the Si film thickness. Final equilibrium is shown to be impacted by Si crystallographic state evolution. Above the Si melting temperature, liquid Si drives SiC interfaces step bunching. When high steps and large terraces are formed over the two SiC surfaces, Si is shown to be trapped within quasi-closed pockets. Eventually, the interface locally closes around these Si inclusions with the creation of SiC/SiC direct contacts. The influence of both annealing temperatures and Si film thickness on all these processes is discussed.

A Comprehensive Study on the Effect of Washing on Nickel-Rich Layered Transition Metal Oxides: Surface Characterization after Li+/H+-Exchange

With an increasing demand for high-capacity cathode active materials (CAMs) for lithium-ion batteries, nickel-rich layered lithium nickel cobalt manganese oxides (NCMs, LiNixCoyMnzO2, with x+y+z = 1) are the currently favored CAMs [1]. However, a higher nickel content does not only increase the specific capacity of NCMs, but also the reactivity of the CAM surface, which makes the material more prone to surface contaminants [2]. These contaminants consist of lithium salts from excess synthesis precursors [3], but can also be formed during improper storage [4,5]. During battery cycling, these contaminants decompose during the first charge/discharge cycles, leading to excessive gassing [6], decomposition of electrolyte solvents and salts [7], as well as to impedance build-up and capacity fading [8].Since these contaminants are generally soluble in water, CAMs are usually washed after synthesis. Exposure to liquid or gaseous water, however, is accompanied by a Li+/H+-exchange, whereby protons intercalate into the CAM [9]. Within the framework of this study, we examine the kinetics of the Li+/H+-exchange for a Ni-rich NCM831205 (LiNi0.83Co0.12Mn0.05O2). The amount of protons inserted into the CAM upon washing was characterized by different methods, namely acid/base titration, thermogravimetric analysis, X-ray powder diffraction, and prompt-gamma activation analysis [10]. The effect of ion-exchanged protons on the electrochemistry was then investigated for NCM831205 samples with 1.0 and 1.5 mol% H+. Here it was found that protonated NCMs can be cycled fully reversibly, yet the capacity fading increases with increasing proton concentration while the rate capability decreases [11].In this work, we now particularly focus on the surface and the bulk of differently washed NCM samples by using X-ray photoelectron spectroscopy (XPS) and X-ray absorption spectroscopy (XAS), respectively. It will be demonstrated that protons intercalate into the near-surface region of the NCM particles, as had only been hypothesized so far [9]. Moreover, the protonated NCM material shows a slightly different Ni-coordination, while maintaining its layered structure. The surface thickness of the protonated layer is determined by quantitative XPS analysis: for example, washing at room temperature for 60 min at a water/CAM mass ratio of 5/1 leads to an approximately 2.5 nm thick protonated surface layer. Lastly, temperature induced phase changes of the protonated surface region are characterized by in-situ by XPS during heating of the sample in vacuum. The data are then correlated with previous results from powder X-ray diffraction. Reference s [1] U. Kim. D. Jun, K. Park, Q. Zhang, P. Kaghazchi, D. Aurbach, D. Major, G. Goobes, M. Dixit, N. Leifer, C. Wang, P. Yan, K. Kim, C. Yoon and Y. Sun, Energy Environ. Sci. 11 1271-1279 (2018).[2] W. Li, E. M. Erickson and A. Manthiram, Nature Energy 5 26 (2020).[3] H.-J. Noh, S. Youn, C.S. Yoon and Y.-K. Sun, J. Power Sources 233 121 (2013).[4]J. Sicklinger, M. Metzger, H. Beyer, D. Pritzl and H.A. Gasteiger,J. Electrochem. Soc. 166 (12) A2322 (2019).[5] L. Hartmann, D. Pritzl, H. Beyer and H.A. Gasteiger, J. Electrochem. Soc. 168 070507 (2021).[6] S. Renfrew and B.D. McCloskey, J. Am. Chem. Soc. 139 17853 (2017).[7] M. Metzger, B. Strehle, S. Solchenbach and H.A. Gasteiger, J. Electrochem. Soc. 163 (7) A1219 (2016).[8] R. Jung, R. Morasch, P. Karayaylali, K. Phillips, F. Maglia, C. Stinner, Y. Shao-Horn and H.A. Gasteiger, J. Electrochem. Soc. 165 (2) A132 (2018).[9] D. Pritzl, T. Teufl, A.T.S. Freiberg, B. Strehle, J. Sicklinger, H. Sommer, P. Hartmann and H.A. Gasteiger, J. Electrochem. Soc. 166 (16) A4056 (2019).[10] S. Oswald, R. Wilhelm, T. Kratky, G. Kieslich, L. Szentmiklósi, B. Maróti, I. Harsányi, M. Piana, S. Günther and H.A. Gasteiger, manuscript in preparation. [11] R. Wilhelm, S. Oswald and H.A. Gasteiger, manuscript in preparation. Acknowledgement This work is financially supported by the German Federal Ministry of Education and Research (BMBF) within the project AQua-POp (grant number 03XP0329B) as well as by the BASF SE Network on Electrochemistry and Battery Research.

Future Green Technology: A Freezing Water Micro-Droplet as an Optical Switch Based on a Time-Domain Photonic Hook.

This paper pays attention to the broader interest of freezing water droplets in mesotronics, particularly to their use as a new all-optical device platform. Here, we show that a freezing mesoscale water droplet with a low Bond number can behave as fully biocompatible natural microlense to form a photonic hook for application in a tunable temperature-controlled optical switch. We first introduced and demonstrated the basic concepts of an optical switch without changes in the wavelength of illumination of a particle or any moving parts being involved. The principle of the operation of the switch is based on the temperature-induced phase change inside the water droplet's refractive index. The simulation results show that the optical isolation of switched channels for an optical switch with linear dimensions of about 15 λ3 based on a freezing water droplet can reach 10 dB in the process of temperature variation at a fixed wavelength. The use of freezing mesoscale droplets acting as a time-domain photonic hook generator open an intriguing route for optical switching in multifunctional green electronics tools for sensing, integrated optics and optical computers.

SLE3S-water system: a linear rheological characterisation

AbstractSurfactant-water mixtures display a complex rheological behaviour, with changes in parameters such as viscosity and moduli of several orders of magnitude as a consequence of phase changes, depending on their concentration and temperature: this criticism heavily affects different industrial processes. In our work, linear rheological behaviour of aqueous mixtures of a commercial anionic surfactant, sodium lauryl ether sulphate, is investigated in a range of temperature (30–60 °C) and surfactant concentration (20–72%wt) of technological relevance. Four phases with different texture are identified by polarised light microscopy: micellar, hexagonal, cubic and lamellar, all showing a shear-thinning behaviour. Rheological parameters of cubic phase show a net jump in a relatively narrow temperature range, suggesting a temperature-induced phase change. The systematic analysis of the rheological behaviour of this widely used surfactant system, reported here for the first time, can be of fundamental support for many industrial applications. Graphical Abstract

Improved MR temperature imaging at 0.5T using view-sharing accelerated multiecho thermometry for MR-guided laser interstitial thermal therapy.

The aim of the current study was to improve temperature-monitoring precision using multiecho proton resonance frequency shift-based thermometry with view-sharing acceleration for MR-guided laser interstitial thermal therapy (MRgLITT) on a 0.5-T low-field MR system. Both precision and speed of the temperature measurement for clinical MRgLITT treatments suffer at low field, due to reduced image signal-to-noise ratio (SNR), decreased temperature-induced phase changes, and limited RF receiver channels. In this work, a bipolar multiecho gradient-recalled echo sequence with a temperature-to-noise ratio optimal weighted echo combination is applied to improve the temperature precision. A view-sharing-based approach is utilized to accelerate signal acquisitions while preserving image SNRs. The method was evaluated using ex vivo (pork and pig brain) LITT heating experiments and in vivo (human brain) nonheating experiments on a high-performance 0.5-T scanner. In terms of results, (1) after echo combination, multiecho thermometry (i.e., ~7.5-40.5ms, 7 TEs) provides ~1.5-1.9 times higher temperature precision than the no echo combination case (i.e., TE7 = 40.5ms) within the same readout bandwidth. Additionally, echo registration is necessary for the bipolar multiecho sequence; (2) for a threefold acceleration, the view-sharing approach with variable-density subsampling shows around 1.8 times lower temperature errors than the GRAPPA method. Particularly for view-sharing, variable-density subsampling performs better than Interleave subsampling; and (3) ex vivo heating and in vivo nonheating experiments demonstrated that the temperature accuracy was less than 0.5 and that the temperature precision was less than 0.6 using the proposed 0.5-T thermometry. It was concluded that view-sharing accelerated multiecho thermometry is a practical temperature measurement approach for MRgLITT at 0.5T.

Strain and temperature induced phase changes inspin‐coated PVDFthin films

AbstractPoly (vinylidene fluoride) (PVDF) is widely utilized for its unique pyro and piezoelectric properties related to its electro‐activeβ‐PVDF. In the past few decades, methods of producingβ‐PVDF by mechanical stretching of non‐polarα‐PVDF have been extensively documented. The aim of the present study is to understand the correlation between phase and mechanical behavior of β‐PVDF obtained directly from spin‐coating, and its stretch‐induced transformation from α‐PVDF. The effect of thermal annealing and in‐plane anisotropy on mechanical properties of spin‐coated PVDF freestanding thin films is investigated, under in‐situ tensile loading, in conjunction with digital image correlation, to measure the full‐field deformation. Stress–strain behavior of spin‐coatedβ‐PVDF andα‐PVDF are correlated with mechanical stretch‐induced phase transformation inα‐PVDF. The mechanical strength and failure strain exhibited by spin‐coated and annealedα‐PVDF (~35 MPa and ~5.5) is much higher than spin‐coatedβ‐PVDF (~10 MPa and ~0.45). The room temperature mechanical stretching causedα‐PVDF toβ‐PVDF beyond a stretch ratio of ~1.2, confirmed by both Fourier transform infrared and Raman spectroscopy. Furthermore, mechanical response and spectroscopic analysis confirmed in‐plane anisotropy due to the spin‐coating process inβ‐PVDF.

Phase-transition-induced thermal hysteresis in Type-II weyl semimetals [formula omitted] and [formula omitted

The resistivity versus temperature measurement is commonly used for identifying temperature-induced phase change and the resulting hysteresis loop. While the resistance is influenced by both the density of states and the carrier lifetimes, the Seebeck coefficient is influenced predominantly by the density of states, and hence is a better probe of the phase of the material. Here, 1T′−Td temperature-induced phase transition in MoTe2 is studied using temperature-dependent X-ray diffraction, resistivity, and Seebeck coefficient measurements. A more distinct hysteresis is observed when measuring the Seebeck coefficient which is consistent with direct measurements of the crystallographic angle using the temperature-dependent X-ray diffraction. The Seebeck and electrical resistivity measurements indicate a competing contribution of the electrons and holes. The contribution of electron pockets becomes more dominant when molybdenum atoms are replaced by tungsten. In MoTe2, a topologically induced enhancement of the Nernst coefficient is observed at low temperatures, and a relatively large phase-transition induced Thomson coefficient of 111 μV⋅K−1 is measured at 254 K which is larger than the Seebeck coefficient measured in the entire temperature range.

Photophysical Behavior of Plant Flavonols Galangin, Kaempferol, Quercetin, and Myricetin in Homogeneous Media and the DMPC Model Membrane: Unveiling the Influence of the B-Ring Hydroxylation of Flavonols.

Flavonols have been studied extensively because of their interesting biological activities and excited-state intramolecular proton transfer (ESIPT) behavior. Galangin, kaempferol, quercetin, and myricetin are structurally related flavonols that differ only in the number of B-ring hydroxyl substituents. In this work, we have carried out a detailed study on the photophysical behavior of these structurally related flavonols in various solvents and a 1,2-dimyristoyl-sn-glycero-3-phosphocholine (DMPC) small unilamellar vesicles (SUVs) model membrane. We observed that these flavonols exist in different forms in the ground and excited states depending on the nature of the solvent. The weak intrinsic fluorescence of these flavonols gets enhanced in hydrogen-bond-accepting and alcoholic solvents. The phototautomer fluorescence intensity of these flavonols increases significantly in the DMPC membrane compared to water, suggesting ESIPT activation via binding interaction between flavonols and the membrane. According to our findings, both the number of B-ring hydroxy groups and membrane fluidity affect the flavonol binding with the membrane. The steady-state fluorescence intensity, steady-state anisotropy, fluorescence lifetime, and fluorescence anisotropy decay of flavonols were sensitive towards the temperature-induced DMPC membrane phase change. A quenching study has been performed to investigate the location and distribution of flavonols in the DMPC SUVs. Moreover, the antioxidant potential of flavonols in DMPC SUVs has been examined using the DPPH scavenging method. Our results reveal that the B-ring hydroxy groups significantly affect the photophysics, binding affinity, location, distribution, and DPPH scavenging activity of polyhydroxy-flavonols in the DMPC SUVs.

Variable stiffness wires based on magnetorheological liquid metals

ABSTRACT Magnetorheological fluid (MRF) has shown its great potential in the development of large mechanical devices, such as dampers, shock absorbers, rotary brakes, clutches, and prosthetic joints. Recently, more research focus has been invested on using MRF to develop soft, stretchable, and miniaturized devices with variable stiffness for realizing functionalities that cannot be achieved using solid smart materials. Here, based on liquid metal magnetoactive slurries (LMMS), a variable stiffness wire with excellent electrical conductivity is demonstrated. Without exposure to a magnetic field, the LMMS wire has an extremely low stiffness, and can be easily stretched while maintaining an excellent electrical conductivity. When applying a magnetic field, the wire becomes much stiffer and can retain its shape even under a load. The combination of properties of flexibility, high electrical conductivity, and variable stiffness of the wire is harnessed to make a flexible gripper that can grasp objects of various shapes. Moreover, by using gallium instead of its liquid metal alloys, the tunable stiffness range of the LMMS wire is significantly enhanced and can be controlled using both external magnetic fields and temperature-induced phase change. The presented LMMS wire has the potential to be applied in flexible electronics, soft robotics and so on.

Susceptibility artifact correction in MR thermometry formonitoring of mild radiofrequency hyperthermia usingtotal field inversion.

MR temperature monitoring of mild radiofrequency hyperthermia (RF-HT) of cancer exploits the linear resonance frequency shift of water with temperature. Motion-induced susceptibility distribution changes cause artifacts that we correct here using the total field inversion (TFI) approach. The performance of TFI was compared to two background field removal (BFR) methods: Laplacian boundary value (LBV) and projection onto dipole fields (PDF). Data sets with spatial susceptibility change and -drift were simulated, phantom heating experiments were performed, four volunteer data sets at thermoneutral conditions as well as data from one cervical cancer, two sarcoma, and one seroma patients undergoing mild RF-HT were corrected using the proposed methods. Simulations and phantom heating experiments revealed that using BFR or TFI preserves temperature-induced phase change, while removing susceptibility artifacts and -drift. TFI resulted in the least cumulative error for all four volunteers. Temperature probe information from four patient data sets were best depicted by TFI-corrected data in terms of accuracy and precision. TFI also performed best in case of the sarcoma treatment without temperature probe. TFI outperforms previously suggested BFR methods in terms of accuracy and robustness. While PDF consistently overestimates susceptibility contribution, and LBV removes valuable pixel information, TFI is more robust and leads to more accurate temperature estimations.

Investigation of NiO reduction dynamics and properties of NiO-Ti powders

Abstract A detailed study of the mechanochemical (MC) processing of NiO-Ti [NiO-Ti (x at.%) with x = 20, 35] powders was carried out using a high-energy ball milling technique to investigate the formation of a NiO-based nanocomposite as a function of the milling time. During milling, the reduction of NiO to Ni follows a gradual process with a reduction of 10% and a self-sustaining process with a maximum reduction of 94% for x = 20 and 35 powders, respectively. The types of NiO reduction and the formation of ferromagnetic (FM) Ni from NiO could be accounted for by the change in magnetization to maximum values of 2 emu/g and 24 emu/g for the gradual and self-sustaining reactions, respectively. The relative fractions of Ni and NiO phases play an important role in (i) the formation of FM nanocomposite, (ii) the enhancement of magnetic anisotropy caused by the coexistence of mixed magnetic phases, (iii) temperature-induced structural phase changes and (iv) the gradual decrease in the induced FM phase with the increase in milling time. The process of time-dependent MC reduction and the resulting structural, vibrational and magnetic behavior of the in situ FM nanocomposite were studied in detail. This process may reveal potential applications in metallurgy and ore reduction processes.

(Energy Technology Division Graduate Student Award Address sponsored by Bio-Logic) Understanding Charge Transport for Current and Future Electrochemical Energy Storage Technologies

Advances in electrochemical energy storage are key for the integration of intermittent wind and solar energy sources into the grid, widespread adoption of electric vehicles, and development of new safe and reliable consumer devices. For grid, transportation, and electronic energy storage markets, each application has distinct needs. Therefore, developing battery technology for emerging and wide-spread applications demands greater understanding of the complex chemical and electrochemical processes that occur within rechargeable batteries. Electron transfer and ion transport are the foundation of battery function where the capacity, loaded voltage and current define the practical energy and power delivery of the system. During operation, repetitive addition and removal of electrons and ions can lead to structural change within the electrode and interfacial formation that can dramatically impact electrochemical outcomes. Thus, structural, chemical, and electrochemical characterization during operation is critically important for next generation electrochemical energy storage technologies. The research efforts highlighted in this talk use multiple advanced characterization techniques, including operando based methods, to probe charge transport properties, structural changes, and interfacial evolution in multiple rechargeable battery systems. Specifically, X-ray absorption spectroscopy enabled structure and oxidation state elucidation in the absence of long-range order. Isothermal microcalorimetry was used to determine heat evolution due to parasitic or decomposition reactions operando. X-ray diffraction was employed to track temperature-induced and lithiation-induced phase changes of distinct electroactive materials. Using advanced characterization, these research efforts provide insight into electron transfer and ion transport properties and their impact on application relevant outcomes (resistance, cycle life, delivered capacity) of electrochemical energy storage technologies.

Unique Design Strategy for Dual Phase Transition That Successfully Validates Dual Switch Implementation in the Dielectric Material.

Dual phase transition/switch materials are a critical cornerstone of information storage and sensing. However, they are difficult to design successfully, and compared with materials showing single-switchable phase transitions, the dual ones retain many challenges by far. Therefore, the significance of a general strategy is far greater than an accidental success. Here, an efficient strategy combining branchlike Et3R and trunklike benzylamine analogues successfully validates dual-switch implementation in the dielectric materials. This inevitable success is based on our treelike analogue mentioned above in which amines with multiple branches can achieve a temperature-induced phase change. Exactly, (BCDA)2ZnBr4 [BCDA = benzyl-(2-chloroethyl)dimethylammonium] proves the regularity and undergoes two reversible phase transitions at 295.4 and 340.8 K, respectively. Variable-temperature single-crystal X-ray diffraction revealed that the generation of double phase transitions is caused by progressive changes of treelike BCDA+ as the temperature rises. Because the permittivity ε' of (BCDA)2ZnBr4 abruptly changed near the phase-transition temperatures, such physical properties make it have latent applicability. In short, the success of our strategy will inspire researches to discover more interesting dual phase transition/switch materials.

Crystal Growth in Mesoporous TiO2 Optical Thin Films

Synthesizing mesoporous TiO2 films with tunable crystallized content, using rapid and facile hydrolytic sol–gel routes, is of interest for developing optical and photocatalytic applications on different substrates. Here, the crystallinity and the porosity of TiO2 is fine-tuned, starting from low annealing temperatures. We further investigate the role of crystal seeds in temperature-induced crystalline phase changes in mesoporous TiO2 thin films by Raman spectroscopy, which is interpreted in the framework of a phonon quantum confinement model. The presence of crystal seeds in the films and the high atomic diffusion in the porous structure lead to the lower activation energy of crystal growth and stabilization of the anatase phase above 700 °C. The film nanostructural and optical properties emphasize the role of complexation by acetylacetone in the formation of nanocrystals and pores. Such fine-tuned optical thin films with varying crystallite and porosity content offer promising perspectives of application...

Long-term stability of guided wave electromagnetic acoustic transducer systems

This article evaluates the long-term stability of a Lorentz force guided wave electromagnetic acoustic transducer. The specific application of the investigated electromagnetic acoustic transducer is pipeline health monitoring using low-frequency (27 kHz) long-range torsional guided waves. There is a concern that repeated swings in the temperature of the structure can cause irreversible changes in the transduction mechanism and therefore pose a risk to the long-term stability of transducers. In this article we report on guided wave signals acquired on a custom-built transducer while it was exposed to more than 90 heating cycles. The highest temperature that was reached during cycling was 80°C and the measurements were acquired over a 14-month period. At the end of the 1-year period, the transducer phase had changed by 23.32° and its amplitude by 3.7%. However, this change was not gradual and most of the change occurred early on, before the highest temperature was first reached in the temperature cycling process. The observed change after this was 6.08° phase shift and 0.9% amplitude change. The possible sources of output changes were investigated, and it was found that the mechanical properties of the contact layer between the electromagnetic acoustic transducer and the pipe surface was very important. A soft silicone interlayer performed best and was able to reduce temperature-induced phase changes in the monitored signals from a maximum of 80 degrees phase change to about 20 degrees phase change, a fourfold reduction.

Measuring Temperature Induced Phase Change Kinetics in Subcutaneous Adipose Tissues Using Near Infrared Spectroscopy, MR Imaging and Spectroscopy and OCT

Monitoring phase transition in adipose tissue and formation of lipid crystals is important in Cryo-procedures such as Selective Cryolipolysis (SC). We exploited a Near-Infrared Spectroscopy (NIRS) method to monitor the onset of fat phase transition (freezing/melting) in human abdominal adipose tissue. The changes in optical scattering were compared to Differential Scanning Calorimetry (DSC) measurements as the gold standard method for measuring phase transition. For some samples, concurrent in vitro measurements of optical scattering using NIRS and the MR signal parameters (T2*) as well as spectral parameters using MR Spectroscopy were performed in a 3 T MR scanner during a cooling/heating cycle. To further investigate phase-transition in adipose tissue in microscopic level, an identical cooling/heating procedure was replicated on a small piece of fat harvested from the same tissue while being imaged under Optical Coherence Tomography (OCT). For all methods, their relationship with temperature shows inflexions in a narrow range, characteristic of lipid phase transition. In particular, the good agreement between DSC and Optical measurements suggests that such NIRS methods can be used to improve dosimetry and to minimize variations of clinical outcome for cryo-procedures.

Numerical modeling of an active elastocaloric regenerator refrigerator with phase transformation kinetics and the matching principle for materials selection

Abstract Elastocaloric cooling technology is a novel solid-state cooling technology based on the latent heat associated with martensitic phase transformation in shape memory alloys. The active elastocaloric regenerator concept was recently demonstrated as a promising approach for this technology. However, if not properly designed, the large temperature gradient in the active regenerators could lead to significant degradation of elastocaloric effect and system performance. To address this challenge, a numerical model was developed in this study with phase transformation kinetics of shape memory alloys, which is capable to investigate the stress-induced or temperature-induced phase change phenomena and elastocaloric effect degradation problem. The performance of an elastocaloric cooling system with a pair of active regenerators is studied in terms of operating frequency, flow rate, geometric parameters and thermal conductivity of the material. Most importantly, the condition to avoid eCE degradation was found as the matching principle to guide material selection for future studies.

Fano resonance engineering in mirror-symmetry-broken THz metamaterials

We introduce a comprehensive approach to the design of mirror-symmetry-broken terahertz (THz) metamaterials and present both the simulation and experimental results which show the desired asymmetric Fano resonances and electromagnetically induced transparency-like windows. With a full-wave simulation, we find these asymmetry-induced resonance modes possess extremely high quality factors and they broaden with an increase in the structure asymmetry. This phenomenon arises from the destructive interference of a super-radiative bright mode and a sub-radiative dark mode which cannot be excited directly. Surface current and electric field distributions are analyzed to explain the emergence of these Fano resonances. An intuitive mechanical coupled oscillator model is derived to explain the unique line-shape of such Fano resonances. Moreover, large resonant frequency tuning (50 GHz) of Fano resonance has been demonstrated by temperature-induced phase change in liquid crystals. We believe that the Fano resonance in THz metamaterials may serve as a strong building block for passive or active THz elements with potential applications for future detection and sensing systems and devices.

Temperature-induced phase changes in bismuth oxides and efficient photodegradation of phenol and p-chlorophenol

A novel, simple and efficient approach for photodegrading phenol and p-chlorophenol, based on BixOy, was reported for the first time. Monoclinic Bi2O4 was prepared by the hydrothermal treatment of NaBiO3·2H2O. A series of interesting phase transitions happened and various bismuth oxides (Bi4O7, β-Bi2O3 and α-Bi2O3) were obtained by sintering Bi2O4 at different temperatures. The results demonstrated that the Bi2O4 and Bi4O7 phase had strong abilities towards the oxidative decomposition of phenol and p-chlorophenol and very high rates of TOC removal were observed. The characterization by XRD and XPS revealed that Bi4+ in Bi2O4 and Bi3.5+ in Bi4O7 were reduced to Bi3+ during the reaction process. Singlet oxygen (1O2) was identified as the major reactive species generated by Bi2O4 and Bi4O7 for the photodegradation of p-chlorophenol and phenol. This novel approach could be used as a highly efficient and green technology for treating wastewaters contaminated by high concentrations of phenol and chlorophenols.