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Special Issue "Microwave Absorbing and Energy Storage Materials"

A special issue of Materials (ISSN 1996-1944).

Deadline for manuscript submissions: closed (15 September 2016)

Special Issue Editor

Guest Editor
Prof. Yuhang Ren

Department of Physics and Astronomy Hunter College, City University of New York, New York, NY 10065, USA
Website | E-Mail

Special Issue Information

Dear Colleagues,

Innovations in tunable microwave elements and energy storage devices often arise from research advances in material chemistry, composite synthesis, and multilayer films that enable new material properties and device functionalities. This Special Issue will include two important types of materials: nonlinear dielectrics and multiferroics.

Nonlinear dielectrics have several characteristics, including high dielectric tunability, large polarizability, and control of phase transitions, which make them unique and of great interest in microwave and capacitor applications. For example, when compared with other devices for energy storage, such as batteries, fuel cells and electrochemical supercapacitors, dielectric capacitors excel in specific power, compactness and cost-effectiveness. As the demand increases for dielectric devices to be made more durable and efficient under high dc-voltage and temperature stress, it becomes crucial to resolve mechanisms of electrical degradation, which lead to increases in leakage current and ultimate breakdown. The mechanisms are usually multifaceted, including both electronic and ionic processes, and involving defects in the bulk phase and at the dielectric interfaces. Many other issues are also important in the field of nonlinear dielectrics, such as (1) new ceramics to improve their energy efficiencies and dielectric strengths while at the same time maintaining their large dielectric constants, (2) ferroelectric films with special domain architectures to delay the polarization saturation, and (3) substrate effects to control the strain field distribution and therefore domain interactions.

Multiferroic composite materials have led to many novel microwave devices, including tunable resonator, phase shifters, and tunable filters, etc. However, it has been challenging in achieving strong magnetoelectric (ME) coupling at microwave frequencies, which is mainly due to the large loss tangent at microwave frequencies from the two constituent phases. Layered composite heterostructures with a magnetic film provide great opportunities for achieving strong ME coupling at microwave frequencies due to minimized charge leakage, large permeability, high self-biased ferromagnetic resonance frequencies and low loss tangents at microwave frequencies associated with magnetic thin films. Most recently, there are many great developments along this direction of research. The field is rapidly advancing into new areas of technologies and discovery.

It is my pleasure to invite you to submit a manuscript for this Special Issue. Full papers, communications, and reviews are all welcome.

Prof. Yuhang Ren
Guest Editor

Manuscript Submission Information

Manuscripts should be submitted online at www.mdpi.com by registering and logging in to this website. Once you are registered, click here to go to the submission form. Manuscripts can be submitted until the deadline. All papers will be peer-reviewed. Accepted papers will be published continuously in the journal (as soon as accepted) and will be listed together on the special issue website. Research articles, review articles as well as short communications are invited. For planned papers, a title and short abstract (about 100 words) can be sent to the Editorial Office for announcement on this website.

Submitted manuscripts should not have been published previously, nor be under consideration for publication elsewhere (except conference proceedings papers). All manuscripts are thoroughly refereed through a single-blind peer-review process. A guide for authors and other relevant information for submission of manuscripts is available on the Instructions for Authors page. Materials is an international peer-reviewed open access monthly journal published by MDPI.

Please visit the Instructions for Authors page before submitting a manuscript. The Article Processing Charge (APC) for publication in this open access journal is 1500 CHF (Swiss Francs). Submitted papers should be well formatted and use good English. Authors may use MDPI's English editing service prior to publication or during author revisions.

Keywords

  • Nonlinear dielectrics
  • Dielectric capacitors
  • Ferroelectrics
  • Multiferroics
  • Electrical degradation in dielectrics
  • Ferromagnetic resonance
  • Ferroelectric domains
  • Strain effect in ferroelectrics
  • Oxygen vacancy migrations
  • Magnetoelectric coupling
  • Composite films

Published Papers (5 papers)

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Research

Open AccessFeature PaperCommunication Preparation of Advanced CuO Nanowires/Functionalized Graphene Composite Anode Material for Lithium Ion Batteries
Materials 2017, 10(1), 72; doi:10.3390/ma10010072
Received: 15 November 2016 / Revised: 11 January 2017 / Accepted: 11 January 2017 / Published: 17 January 2017
PDF Full-text (5658 KB) | HTML Full-text | XML Full-text | Supplementary Files
Abstract
The copper oxide (CuO) nanowires/functionalized graphene (f-graphene) composite material was successfully composed by a one-pot synthesis method. The f-graphene synthesized through the Birch reduction chemistry method was modified with functional group “–(CH2)5COOH”, and the CuO nanowires (NWs) were well
[...] Read more.
The copper oxide (CuO) nanowires/functionalized graphene (f-graphene) composite material was successfully composed by a one-pot synthesis method. The f-graphene synthesized through the Birch reduction chemistry method was modified with functional group “–(CH2)5COOH”, and the CuO nanowires (NWs) were well dispersed in the f-graphene sheets. When used as anode materials in lithium-ion batteries, the composite exhibited good cyclic stability and decent specific capacity of 677 mA·h·g−1 after 50 cycles. CuO NWs can enhance the lithium-ion storage of the composites while the f-graphene effectively resists the volume expansion of the CuO NWs during the galvanostatic charge/discharge cyclic process, and provide a conductive paths for charge transportation. The good electrochemical performance of the synthesized CuO/f-graphene composite suggests great potential of the composite materials for lithium-ion batteries anodes. Full article
(This article belongs to the Special Issue Microwave Absorbing and Energy Storage Materials)
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Open AccessCommunication Well-Dispersed Co/CoO/C Nanospheres with Tunable Morphology as High-Performance Anodes for Lithium Ion Batteries
Materials 2016, 9(12), 955; doi:10.3390/ma9120955
Received: 17 October 2016 / Revised: 14 November 2016 / Accepted: 18 November 2016 / Published: 24 November 2016
PDF Full-text (4697 KB) | HTML Full-text | XML Full-text | Supplementary Files
Abstract
Well-dispersed Co/CoO/C nanospheres have been designed and constructed through a facile electrospinning method with a strategy controlling the morphology of nanocomposites via adjusting the pre-oxidized and heat treatments. Scanning electron microscopy results reveal that the as-synthesized sample pre-oxidized at 275 °C shows better
[...] Read more.
Well-dispersed Co/CoO/C nanospheres have been designed and constructed through a facile electrospinning method with a strategy controlling the morphology of nanocomposites via adjusting the pre-oxidized and heat treatments. Scanning electron microscopy results reveal that the as-synthesized sample pre-oxidized at 275 °C shows better spherical morphology with a diameter of around 300 nm without conspicuous agglomeration. X-ray diffraction analysis confirms the coexistence of cobalt and cobalt monoxide in the sample. Furthermore, the electrochemical tests reveal that the sample pre-oxidized at 275 °C displays excellent cycling stability with only 0.016% loss per cycle even after 400 cycles at 1000 mA·g−1 and enhanced high-rate capability with a specific discharge capacity of 354 mA·g−1 at 2000 mA·g−1. Besides, the sample pre-oxidized at 275 °C shows a specific capacity of 755 mA·g−1 at 100 mA·g−1 after 95 cycles. The improved electrochemical performance has been ascribed to the well dispersion of nanospheres, the improved electronic conductivity, and the structural integrity contribution from the carbon and cobalt coexisting nanocomposite. The strategy for preparing well-dispersed nanospheres by adjusting pre-oxidized and annealing processes could have insight for other oxide nanosphere synthesis. Full article
(This article belongs to the Special Issue Microwave Absorbing and Energy Storage Materials)
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Open AccessFeature PaperCommunication Energy Storage Characteristics of BiFeO3/BaTiO3 Bi-Layers Integrated on Si
Materials 2016, 9(11), 935; doi:10.3390/ma9110935
Received: 29 September 2016 / Revised: 27 October 2016 / Accepted: 11 November 2016 / Published: 18 November 2016
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Abstract
BiFeO3/BaTiO3 bi-layer thick films (~1 μm) were deposited on Pt/Ti/SiO2/(100) Si substrates with LaNiO3 buffer layers at 500 °C via a rf magnetron sputtering process. X-ray diffraction (XRD) analysis revealed that both BiFeO3 and BaTiO3
[...] Read more.
BiFeO3/BaTiO3 bi-layer thick films (~1 μm) were deposited on Pt/Ti/SiO2/(100) Si substrates with LaNiO3 buffer layers at 500 °C via a rf magnetron sputtering process. X-ray diffraction (XRD) analysis revealed that both BiFeO3 and BaTiO3 layers have a (00l) preferred orientation. The films showed a small remnant polarization (Pr ~ 7.8 μC/cm2) and a large saturated polarization (Ps ~ 65 μC/cm2), resulting in a slim polarization-electric field (P-E) hysteresis loop with improved energy storage characteristics (Wc = 71 J/cm3, η = 61%). The successful “slim-down” of the P-E loop from that of the pure BiFeO3 film can be attributed to the competing effects of space charges and the interlayer charge coupling on charge transport of the bi-layer film. The accompanying electrical properties of the bi-layer films were measured and the results confirmed their good quality. Full article
(This article belongs to the Special Issue Microwave Absorbing and Energy Storage Materials)
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Open AccessArticle Investigation of Electric Field–Induced Structural Changes at Fe-Doped SrTiO3 Anode Interfaces by Second Harmonic Generation
Materials 2016, 9(11), 883; doi:10.3390/ma9110883
Received: 16 September 2016 / Revised: 18 October 2016 / Accepted: 27 October 2016 / Published: 31 October 2016
PDF Full-text (5146 KB) | HTML Full-text | XML Full-text
Abstract
We report on the detection of electric field–induced second harmonic generation (EFISHG) from the anode interfaces of reduced and oxidized Fe-doped SrTiO3 (Fe:STO) single crystals. For the reduced crystal, we observe steady enhancements of the susceptibility components as the imposed dc-voltage
[...] Read more.
We report on the detection of electric field–induced second harmonic generation (EFISHG) from the anode interfaces of reduced and oxidized Fe-doped SrTiO3 (Fe:STO) single crystals. For the reduced crystal, we observe steady enhancements of the susceptibility components as the imposed dc-voltage increases. The enhancements are attributed to a field-stabilized electrostriction, leading to Fe:Ti-O bond stretching and bending in Fe:Ti-O6 octahedra. For the oxidized crystal, no obvious structural changes are observed below 16 kV/cm. Above 16 kV/cm, a sharp enhancement of the susceptibilities occurs due to local electrostrictive deformations in response to oxygen vacancy migrations away from the anode. Differences between the reduced and oxidized crystals are explained by their relative oxygen vacancy and free carrier concentrations which alter internal electric fields present at the Pt/Fe:STO interfaces. Our results show that the optical SHG technique is a powerful tool for detecting structural changes near perovskite-based oxide interfaces due to field-driven oxygen vacancy migration. Full article
(This article belongs to the Special Issue Microwave Absorbing and Energy Storage Materials)
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Open AccessArticle Dielectric Characteristics and Microwave Absorption of Graphene Composite Materials
Materials 2016, 9(10), 825; doi:10.3390/ma9100825
Received: 12 September 2016 / Revised: 27 September 2016 / Accepted: 2 October 2016 / Published: 13 October 2016
Cited by 4 | PDF Full-text (4328 KB) | HTML Full-text | XML Full-text
Abstract
Nowadays, many types of materials are elaborated for microwave absorption applications. Carbon-based nanoparticles belong to these types of materials. Among these, graphene presents some distinctive features for electromagnetic radiation absorption and thus microwave isolation applications. In this paper, the dielectric characteristics and microwave
[...] Read more.
Nowadays, many types of materials are elaborated for microwave absorption applications. Carbon-based nanoparticles belong to these types of materials. Among these, graphene presents some distinctive features for electromagnetic radiation absorption and thus microwave isolation applications. In this paper, the dielectric characteristics and microwave absorption properties of epoxy resin loaded with graphene particles are presented from 2 GHz to 18 GHz. The influence of various parameters such as particle size (3 µm, 6–8 µm, and 15 µm) and weight ratio (from 5% to 25%) are presented, studied, and discussed. The sample loaded with the smallest graphene size (3 µm) and the highest weight ratio (25%) exhibits high loss tangent (tanδ = 0.36) and a middle dielectric constant ε′ = 12–14 in the 8–10 GHz frequency range. As expected, this sample also provides the highest absorption level: from 5 dB/cm at 4 GHz to 16 dB/cm at 18 GHz. Full article
(This article belongs to the Special Issue Microwave Absorbing and Energy Storage Materials)
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