Material Matters in the Physics Classroom

Photonic crystals are periodic dielectric structures which selectively tune the wavelengths of light propagating through the material1 2. The highly ordered, repeating structural lattice induces a photonic bandgap or stopband which inhibits or partially attenuates certain frequencies of light, similar to the electronic bandgap with forbidden energies present in semiconductor materials3. These forbidden frequencies are blocked in transmission and reflected from the material surface. The inherent sensitivity of this photonic response to repeating lattice size dimensions and the magnitude of the refractive index contrast between the constituent materials allows for tailored optical behaviour by adjusting the photonic crystal structural parameters or environment4 5.A range of interesting applications using both the photonic bandgap and material porosity have emerged, predicated on the ability to accurately forecast the wavelength position of the photonic response. Colorimetric sensors6 7, photocatalysts8 9 and solar cells10 are prime examples of these types of applications; the porosity of the photonic crystal facilitates greater material infiltration and reactions, while the photonic bandgap acts to enhance the optical component of the process. Critically, the use of these structures is tied to our ability to predict and interpret the signature optical response.Here, we examine several techniques which can be used modify the photonic bandgap/stopband for photonic crystal structures. For TiO2 and SnO2 inverse opal photonic crystals, we explore how solvent infiltration into the highly porous network red-shifts the observed photonic response. Using solvents with different refractive indices, we apply the shifted photonic stopband data to determine the fill fraction of solid material comprising the photonic crystal network. We also examine functionalization of artificial opal and inverse opal photonic crystals with metal films. We detail the emergence of a consistent photonic stopband blue-shift with increasing metal content and propose a reduction in the effective refractive index of the entire photonic crystal introduced by the specific properties of the metal film. Importantly, the effects investigated here are broadly applicable to a range of realistic operating conditions across many disciplines where an understanding of the photonic stopband is paramount to the application. References Yablonovitch, E., Inhibited Spontaneous Emission in Solid-State Physics and Electronics. Physical Review Letters 1987, 58 (20), 2059-2062.John, S., Strong localization of photons in certain disordered dielectric superlattices. Physical Review Letters 1987, 58 (23), 2486-2489.Joannopoulos, J. D.; Villeneuve, P. R.; Fan, S., Photonic crystals: putting a new twist on light. Nature 1997, 386 (6621), 143-149.Blanford, C. F.; Schroden, R. C.; Al-Daous, M.; Stein, A., Tuning Solvent-Dependent Color Changes of Three-Dimensionally Ordered Macroporous (3DOM) Materials Through Compositional and Geometric Modifications. Advanced Materials 2001, 13 (1), 26-29.Aguirre, C. I.; Reguera, E.; Stein, A., Tunable Colors in Opals and Inverse Opal Photonic Crystals. Advanced Functional Materials 2010, 20 (16), 2565-2578.Zhang, Y.; Qiu, J.; Hu, R.; Li, P.; Gao, L.; Heng, L.; Tang, B. Z.; Jiang, L., A visual and organic vapor sensitive photonic crystal sensor consisting of polymer-infiltrated SiO2 inverse opal. Physical Chemistry Chemical Physics 2015, 17 (15), 9651-9658.Li, H.; Chang, L.; Wang, J.; Yang, L.; Song, Y., A colorful oil-sensitive carbon inverse opal. Journal of Materials Chemistry 2008, 18 (42), 5098-5103.Chen, J. I. L.; von Freymann, G.; Choi, S. Y.; Kitaev, V.; Ozin, G. A., Amplified Photochemistry with Slow Photons. Advanced Materials 2006, 18 (14), 1915-1919.Collins, G.; Lonergan, A.; McNulty, D.; Glynn, C.; Buckley, D.; Hu, C.; O'Dwyer, C., Semiconducting Metal Oxide Photonic Crystal Plasmonic Photocatalysts. Advanced Materials Interfaces 2020, 7 (8), 1901805.Liu, L.; Karuturi, S. K.; Su, L. T.; Tok, A. I. Y., TiO2 inverse-opal electrode fabricated by atomic layer deposition for dye-sensitized solar cell applications. Energy & Environmental Science 2011, 4 (1), 209-215. Figure 1 SEM images and optical transmission spectra for (a) TiO2 and (b) SnO2 inverse opals. In each case the wavelength position of the photonic stopband is red-shifted significantly when a solvent infiltrates the porous photonic crystal network. SEM images and optical transmission spectra for (c) artificial polystyrene opals coated with a gold film and (d) TiO2 inverse opals coated with a copper film. Metal film incorporation into the photonic crystal network acts to consistent blue-shift the observed photonic stopband. Figure 1

NdFeB (Neodymium magnets) rare earth permanent magnet is an advanced magnetic material characterized by a high energy product and excellent magnetic performance, which has broad application prospects. With the rapid development of 3D printing technology, its application in the research and fabrication of rare earth permanent magnet materials has become a research hotspot. This paper reviews the latest research developments of rare earth permanent magnet NdFeB materials in 3D printing. It introduces the basic properties and applications of rare earth permanent magnet materials and highlights the main challenge these materials faced, which is how do we improve their solid content. Additionally, the advantages and challenges of 3D printing technology in preparing rare earth permanent materials are analyzed in this paper. By comparing the variations in magnet properties of ferrite and rare permanent magnet materials with increasing temperature, it is found that the latter have relatively poor magnetic stability at high temperatures. Based on these points, the paper summarizes optimization methods of the current 3D printing process for rare earth permanent magnet materials. Finally, the paper discusses the development prospects of rare earth permanent magnet materials in 3D printing, as well as problems need to be solved and future research directions.

Nowadays, many applications are demanding more and more compact, cost effective, and robust electric drives. By using rare earth magnets, it is possible to achieve electrical machines with rather high torque volume ratio, accomplishing this way the compactness requirement. Nevertheless, rare earth permanent magnets are very sensitive to the temperature, so that the risk of being partially demagnetized arises as their working temperature increases. In addition, as it has been seen during the last years, the market of rare earth metals is quite volatile. The price of magnets could rise suddenly, leading to a significant impact on the cost, and so in the competitiveness of permanent magnet machines. Due to this fact, it is essential to reduce the dependency on rare earth market in order to accomplish cost-effective drive solutions. Some key points to face this problem can be to reduce the magnet volume, or to use magnets with worse thermal properties (magnets with less dysprosium). Nevertheless, in both cases, the adopted solution would lead to an increase in the risk of demagnetization, affecting to the robustness of the machine. In this paper, a methodology based on finite element analysis and experimental test is proposed to evaluate the demagnetization risk in permanent magnet machines. By applying this methodology, it is possible to accomplish competitive machine designs, achieving a good tradeoff between cost and robustness. The proposed methodology has been applied in a practical case, for the optimization of ten industrial motors, achieving good results.

Rare earth permanent magnets (REPMs) feature high magnetic performance, and are very suitable for use in electric machine applications. In this paper, some calculation and analysis methods of REPM electric machines are given and summarised. Some kinds of REPM machines developed in China's Shenyang University of Technology are also presented.

By analogy to electron waves in a crystal, light waves in a 3-D periodic dielectric structure should be described by band theory. Recently, the idea of photonic band structure1 has been introduced. This means that the concepts of reciprocal space, Brillouin zones, dispersion relations, Bloch wave functions, Van Hove singularities, etc. must now be applied to optical waves. If the depth of index of refraction modulation is sufficient, a photonic band gap can exist. This is an energy band in which optical modes, spontaneous emission, and zero point fluctuations are all absent. Therefore, inhibited spontaneous emission can now begin to play a role in a semiconductors and solid-state electronics. It makes sense then to speak of photonic band structure and of a photonic reciprocal space, which has a Brillouin zone ~1000 times smaller than the Brillouin zone of the electrons. If the dielectric constant is periodically modulated in all three dimensions, it is possible to have a photonic band gap which overlaps the electronic band edge and for spontaneous electron-hole recombination to be rigorously forbidden. Indeed the photonic band gap is essentially ideal since the dielectric response can be real and dissipationless. It is interesting that the most natural real space structure for the optical medium is face centered cubic (fee), which is also the most famous atomic arrangement in crystals. The comparison between electronic and photonic band structure is revealing: (a) The underlying dispersion relation for electrons is parabolic, while that for photons is linear. (b) The angular momentum of electrons is 1/2, but the scalar wave approximation is frequently made; in contrast, photons have spin 1 and the vector wave character will likely play a major role in the band structure. (c) The band theory of electrons is only an approximation due to electron-electron repulsion, while photonic band theory is essentially exact since photon interactions are negligible.

The physical metallurgy and processing of sintered rare earth permanent magnets

Rare earth permanent magnets play a key role in view of the increasing market for green energy applications and new materials which can compete with Nd2Fe14B but are environmentally less problematic are highly sought after. Fe-based ThMn12 phases contain less RE material than the commercially used compounds and have attracted quite some interest. An efficient and resource saving way to identify out of this class new phases which have the potential to become permanent magnets is by computational materials design. However, predicting the magnetic properties of 4f systems is challenging because of the localization of the 4f electrons which determines to a large extend the level of theory needed for a reliable description and prediction.We have shown that the 4f electrons in Sm 1:12 can be viewed as fully localized and can be safely treated as core electrons while for CeFe11Ti the correlation effects are smaller and the 4f states can still be viewed as valence states [1,2]. In the case of NdFe11Ti the 4f electrons are partially localized as can be seen from the hybridization function in Fig. 1. The hybridization function serves as a qualitative measure for the interaction of the 4f electrons with the valence electrons in a system [3].As a consequence of the partial localization, the cone type magnetocrystalline anisotropy (MCA) of the latter system is only observed in a DFT+U description with an intermediate Hubbard U value, see Fig. 2. Assuming full localization (4f in core) results in a uniaxial MCA which contradicts the experimental findings at low temperatures. Plain DFT also fails. It is also discussed in how far the strong dependence of the MCA and related magnetic properties of NdFe11Ti on the theoretical description influences the prediction of new phases. As test case the quaternary system Nd1-xYxFe12-yTiy was chosen.Supported by NOVAMAG (EU686056), the Swedish Foundation for Strategic Research (EM16-0039), and SNIC(Swedish National Infrastructure for Computing).   New potential materials for rare earth lean permanent magnets from computational design and the challenge of the 4f electrons

First-principles study of structural stability and magnetic properties of Sm2Co17 rare earth permanent magnets doped with transition metal elements☆

Permanent magnet synchronous motors (PMSMs) are a key part of the current hybrid electric vehicle (HEV) drive system, and the sophisticated performance such as small size, high power density, and high efficiency is required to the PMSMs in the HEV drive system. Therefore, rare earth permanent magnet is generally employed in the PMSMs in order to satisfy those demands. However, rare earth materials contained in the rare earth permanent magnet have several concerns caused by uneven distribution, because the rare earth materials such as neodymium and dysprosium depend on China for 90% or more of the world share. Accordingly, the rare earth materials have the undeniable possibility of sudden rise of price or reinforcement of export restriction. On the other hand, the HEVs tend to be promoted rapidly because of growing concern about environmental problems. Therefore, it is very important to develop rare-earth-free motors for the next generation HEV drive system. This paper proposes a ferrite permanent magnet axial gap motor without the rare earth materials for the HEVs. In addition, the proposed motor structure and the analytical results with the 3D-FEA are introduced.

ADVERTISEMENT RETURN TO ISSUEPREVReviewNEXTHigh-Q Optical Sensors for Chemical and Biological AnalysisMatthew S. Luchansky and Ryan C. Bailey*View Author Information Department of Chemistry, University of Illinois at Urbana−Champaign, 600 South Mathews Avenue, Urbana, Illinois 61801, United States*E-mail: [email protected]. Address: 44 Roger Adams Lab 600 South Mathews Avenue, Urbana, IL, 61801. Phone: (217) 333-0676.Cite this: Anal. Chem. 2012, 84, 2, 793–821Publication Date (Web):November 23, 2011Publication History Published online23 November 2011Published inissue 17 January 2012https://pubs.acs.org/doi/10.1021/ac2029024https://doi.org/10.1021/ac2029024review-articleACS PublicationsCopyright © 2011 American Chemical SocietyRequest reuse permissionsArticle Views6236Altmetric-Citations223LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InRedditEmail Other access optionsGet e-Alertsclose SUBJECTS:Assays,Crystals,Nanoparticles,Quantum mechanics,Sensors Get e-Alerts

The Federal Government of Nigeria, in its National Policy on Education (Federal Republic of Nigeria, 2014), recognizes the prominent role of ICTs in the modern world. This study examined the extent to which Information Communication Technology (ICT) is integrated into various Physics Concepts in Secondary schools Curriculum as well as Teachers' Self Efficacy about ICTs Integration in Physics Class Rooms in Kano State, Nigeria. Descriptive survey design was used to collect data on Teachers' Self Efficacy and ICTs Integration (TIIQ) from 56 Physics teachers drawn from Science Colleges in Kano Metropolis. The TII Questionnaire was validated by specialists in science and Computer Education. Analysis of the results reveals that majority of the teachers (80.35%) believed that they are literate enough to incorporate ICTs in Physics class room but the extent of integration of ICTs into Senior Secondary Physics Education is minimal and to a large extent inadequate. It was recommended among others that the use of ICTs for instructional delivery should be incorporated into teacher training programs of pre-service and in-service Physics teachers.

A column filled with micro polymer inclusion beads (µPIBs) was developed and investigated for the first time. The µPIBs were composed of 60 wt% di-(2-ethyl-hexyl) phosphoric acid (D2EHPA) and 40 wt% poly(vinyl chloride) (PVC) and the column was used for the separation of ions of rare earth elements (REEs) from synthetic solutions and the digest of end-of-life (EOL) rare earth permanent magnets (REPMs). This µPIB packed column was successfully applied to separating La3+ from Gd3+, as representatives of the light and middle REEs, previously achieved by us using a polymer inclusion membrane (PIM) containing the same chemical components as the µPIBs used in this study. The results obtained demonstrated the feasibility of the µPIBs packed in a column for light and middle REE ion separation similarly to their PIM counterpart. The separation potential of the µPIB packed column was further demonstrated by the selective recovery of Nd3+ and Dy3+ from an EOL REPM digest in 2 M sulfuric acid which also contained Fe3+, Co2+, and Ni2+. Nd3+ and Dy3+ could be selectively extracted from the diluted to 0.03 M sulfuric acid digest after the addition of ascorbic acid which reduced Fe3+ to Fe2+. Nd3+ and Dy3+ were separated via selective back-extraction from the µPIB-column using 0.3 and 2 M sulfuric acid receiving solutions, respectively. Thermogravimetric analysis of the µPIBs, before and after application in the µPIB-column, indicated negligible D2EHPA loss after six processing cycles. Thus, these results demonstrated the strong potential of the proposed µPIB-column method for the sustainable recovery of REEs from electronic waste such as REPMs.

Recovery of rare earth elements (REEs) from end‐of‐life (EOL) products represents a strategic opportunity to strengthen the domestic supply chain for rare earth elements. This work presents a superstructure‐based optimization framework for finding the most economical processing pathway for different EOL rare earth permanent magnets (REPMs). The framework evaluates state‐of‐the‐art technologies across four processing stages—disassembly, demagnetization, leaching and extraction, and precipitation and calcination—using net present value (NPV) maximization and cost of recovery (COR) minimization objectives. A novel bottom‐up costing framework for hydrogen decrepitation is also introduced. Two feedstocks were considered: REPMs from EOL hard disk drives (HDDs), and electric and hybrid electric vehicles (EVs and HEVs). While HDD recycling proved unprofitable due to limited feedstock availability, EVs/HEVs were profitable across a range of parameters and cost estimates. Therefore, our findings suggest that the proposed EOL EV/HEV recycling process may be economical and is worthy of further investigation.

Computer numerical simulations for accelerated design of rare earth permanent magnet motors in renewable energy applications: A review

The behavior of light waves in a homogeneous dielectric crystal is the same as that in a continuous medium, because the wavelength of light is much larger than the period of crystal lattice, or say, the wave vector of light is much smaller than the reciprocal vectors of crystal lattice. However, if some microstructure is introduced into a dielectric crystal, forming a superlattice, and if the periods of the superlattice are comparable with the light wavelength, the situation is quite different. The propagation of light wave in the superlattice (classical system) is similar to the electron motion in a periodic potential of crystal lattice (quantum system). Thus, some ideas in solid-state electronics - for example, the reciprocal space, Brillouin zone, dispersion relation and the like - may be used in light wave processes. Such is the case for photonic crystal. On the other hand the interactions between light wave vectors and reciprocal vectors provided by the superlattice may generate some physical effects. It is the interactions that have led to new frequency generations in the quasi-phase matching materials. The main achievements in the field mentioned are reviewed.