Brian C. Riggs

Preparation of BaTiO3/low melting glass core–shell nanoparticles for energy storage capacitor applications

A core–shell nano-scale mixing technique was applied to fabricate BaTiO3/glass nanocomposites in order to preserve the nano-grain dielectric properties of BaTiO3 after sintering and enhance the bulk composite energy storage capability. Coating layers of low melting glasses of lead borosilicate glass (65PbO–20B2O3–15SiO2, mol%) and bismuth borosilicate glass (65Bi2O3–20B2O3–15SiO2, mol%) were deposited onto BaTiO3 nanoparticles in chemical solution by a sol-precipitation method under ultrasonic agitation. Transmission electron microscopy (TEM) results confirmed the formation of core–shell nanostructures with controllable shell thicknesses between 2 and 18 nm. X-ray diffraction (XRD) patterns showed that no crystalline peaks were detected from the glass coating layer. Fourier transform infrared (FT-IR) spectra indicated a glass network structure of lead borosilicate glass and bismuth borosilicate glass, respectively. High densifications were achieved for both composites by sintering at low temperatures (≤900 °C). Noticeable grain growth was observed for the lead borosilicate glass-coated BaTiO3 (Pb-BT) composite while almost no grain growth was observed for the bismuth borosilicate glass-coated BaTiO3 (Bi-BT) nanocomposite. This disparity was attributed to the different interactions between the BaTiO3 core and two glasses during the sintering process, as revealed by the XRD study. Dielectric properties and energy storage capability of the Bi-BT nanocomposite were investigated in detail. The Bi-BT nanocomposite showed high polarization, high dielectric breakdown strength (≥1000 kV cm−1), postponed polarization saturation, and low remnant polarization with the discharge energy density of ∼10 J cm−3 at 1000 kV cm−1. Thus, the Bi-BT core–shell nanocomposite appears to be a promising material system for energy storage capacitor applications.

Synthesis and characterization of lead-free ternary component BST–BCT–BZT ceramic capacitors

Polycrystalline sample of lead-free 1/3(Ba0.70Sr0.30TiO3) + 1/3(Ba0.70Ca0.30TiO3) + 1/3(BaZr0.20Ti0.80O3)(BST-BCT-BZT) ceramic was synthesized by solid state reaction method. Phase purity and crystal structure of as-synthesized materials was confirmed by X-ray diffraction (XRD). Temperature-dependent dielectric permittivity studies demonstrated frequency-independent behavior, indicating that the studied sample has typical diffuse phase transition behavior with partial thermal hysteresis. A ferroelectric phase transition between cubic and tetragonal phase was noticed near room temperature (~ 330 K). Bulk P–E hysteresis loop showed a saturation polarization of 20.4 μC/cm2 and a coercive field of ~ 12.78 kV/cm at a maximum electric field of ~ 115 kV/cm. High dielectric constant (e ~ 5773), low dielectric loss (tan δ ~ 0.03) were recorded at room temperature. Discharge energy density of 0.44 J/cm3 and charge energy density of 1.40 J/cm3 were calculated from nonlinear ferroelectric hysteresis loop at maximum electric field. Dielectric constant at variable temperatures and electric fields, ferroelectric to paraelectric phase transition and energy storage properties were thoroughly discussed.

Click-In Ferroelectric Nanoparticles for Dielectric Energy Storage

Polymer-ceramic nanocomposites have been thoroughly investigated previously for high energy storage devices. However, the increase in performance of these nanocomposites has proven to be significantly lower than predicted values. Through surface functionalization of high dielectric constant nanoparticles (NP), the flaws that reduce composite performance can be eliminated to form high energy density composite materials. Functionalization methods utilize high throughput printing and curing techniques (i.e., inkjet printing and xenon flash lamp curing) that are crucial for rapid adoption into industrial production. (Ba,Ca) (Zr,Ti)O3 NPs (50 nm) are synthesized through the solvothermal method and functionalized with alkene terminated methoxysilanes. A thiol-ene monomer ink system, PTD3 [pentaerythritol tetrakis (3-mercaptopropionate) (PEMP, P), 1,3-Diisopropenylbenzene (DPB, D), 2,4,6-Triallyloxy-1,3,5-triazine (TOTZ, T)], is used as a high breakdown polymer matrix. Neat polymer, alkene terminated NP-polymer composites, and hydrophilic, TBAOH functionalized NP-polymer composites were spin coated onto both copper laminated glass slides and printed onto copper substrates in 1 cm(2) patterns for testing. Alkene functionalized NPs increased the breakdown strength by ∼38% compared to the nonfunctionalized NPs. Functionalized NPs increased both the breakdown strength and dielectric constant compared to the neat polymer, increasing the energy density nearly 3-fold from 13.3 to 36.1 J·cm(-3).

Structure, Ferroelectric, Dielectric and Energy Storage Studies of Ba0.70Ca0.30TiO3, Ba(Zr0.20Ti0.80)O3 Ceramic Capacitors

Ba0.70Ca0.30TiO3-(BCT),Ba(Zr0.2Ti0.8)O3-(BZT) ceramics were fabricated by conventional mixed oxide route to develop inorganic dielectric materials suitable for use as an insulator with high dielectric constant and low energy loss for capacitor applications. The structural phase transition, ferroelectric, dielectric and energy storage properties of BCT, BZT ceramic capacitors were investigated. Room temperature X-ray diffraction (XRD) patterns revealed prominent peaks corresponding to tetragonal perovskite crystal structure for both BCT, BZT solid solutions. Slim ferroelectric hysteresis (P-E) loops were observed for BCT, BZT solid solutions. Temperature dependent dielectric property measurements of BCT, BZT solid solutions have shown a high dielectric constant and low dielectric loss. Room temperature (300K) breakdown field strength and energy densities were obtained from the integral area of P-E loops. For the BCT ceramics, the largest recoverable energy (unreleased energy) density is 1.41 J/cm3 with dielectric breakdown strength as high as 150 kV/cm. For the BZT ceramics, the largest recoverable energy (unreleased energy) density is 0.71 J/cm3 with dielectric breakdown strength as high as 150 kV/cm. Bulk BCT, BZT ceramics have shown interesting energy densities; these might be the strong candidate materials for capacitor applications.

Surface modified BaTiO 3 -polystyrene nanocomposites for energy storage

Major research efforts have been focused towards developing high dielectric constant ( e ), low loss (tan δ ) and high electrical breakdown dielectrics for energy storage capacitors. Combining the low cost, ease of processing and high breakdown field strength (BDS) of polymers with the high e ceramic fillers will result in high-energy storage capacitors. Herein, we show progress in developing low cost, low weight and high electrical energy storage capacitors by mixing polystyrene (PS, mw = 177,000 g/mol) and hydroxyl-BaTiO 3 nanoparticles ( h -BT, ~50 nm) in a highly polar solvent (DMF) on weight percent basis. Surface modification of crude-BT( c -BT) by H 2 O 2 resulted in h -BT, which renders h -BT highly dispersed due to the surface hydroxyl functional groups. Ceramic-polymer nanocomposites (80PS-20 h BT and 20PS-80 h BT) exhibited relatively high BDS (~475 kV/cm and 247 kV/cm) and a large e (~13 and 40). Room temperature (300 K) energy density values for PS, 80PS-20 h BT, 20PS-80 h BT and h -BT are 4.33, 0.12, 0.10 and 0.36 J/cm 3 , respectively.

Photonic curing of aromatic thiol–ene click dielectric capacitors via inkjet printing

Dielectric capacitive energy storage has a wide range of applications such as microelectronic devices, grid scale load leveling, military applications, and personal power supplies. The high charge and discharge rate, along with the high retention and fatigue properties, make dielectric capacitors an attractive means of energy storage. Device manufacturing in industry requires high throughput and high pattern registry printing processes, such as inkjet, that are able to deposit a wide variety of materials. Thiol–alkene systems, [pentaerythritol tetrakis(3-meracproprinate) (PEMP, P), 1,3-diisopropenylbenzene (DPB, D), 2,4,6-triallyoxy-1,3,5-triazine (TOTZ, T)] of various compositions were printed via inkjet printing and cured with a xenon flash lamp system. For simplicity, inks were designated PTD0–4, correlating to the amount of DPB in the ink. PTD1–4 demonstrated fluid properties amenable to inkjet printing (with Z factors between 2–11) and were cured to produce mechanically and chemically stable dielectric films. PTD3 showed the best printability and was used for characterization of energy storage. It was found that the dielectric constant varied with curing intensity and energy/voltage. The breakdown strength had no correlation to the curing parameters tested. Weibull analysis of breakdown failure along with dielectric characterization resulted in a volumetric energy density distribution with a peak characteristic energy storage (63% chance of failure) of 32 J cm−3.

Laser direct-write based fabrication of a spatially-defined, biomimetic construct as a potential model for breast cancer cell invasion into adipose tissue.

Epithelial-adipose interaction is an integral step in breast cancer cell invasion and progression towards lethal metastatic disease. Understanding the physiological contribution of obesity, a major contributor to breast cancer risk and negative prognosis in post-menopausal patients, on cancer cell invasion requires detailed co-culture constructs that reflect mammary microarchitecture. Using laser direct-write, a laser-based CAD/CAM bioprinting technique, we have demonstrated the ability to construct breast cancer cell-laden hydrogel microbeads into spatially defined patterns in hydrogel matrices containing differentiated adipocytes. Z-stack imaging confirmed the three-dimensional nature of the constructs, as well as incorporation of cancer cell-laden microbeads into the adipose matrix. Preliminary data was gathered to support the construct as a potential model for breast cancer cell invasion into adipose tissue. MCF-7 and MDA-MB-231 breast cancer cell invasion was tracked over 2 weeks in an optically transparent hydrogel scaffold in the presence of differentiated adipocytes obtained from normal weight or obese patient tissue. Our model successfully integrates adipocytes and gives us the potential to study cellular and tissue-level interactions towards the early detection of cancer cell invasion into adipose tissue.

Thermal characterization of concentrated solar absorbance using resistive heaters

Thermal management of concentrated photovoltaics (CPV) is necessary in order to optimize cell performance and prevent thermal damage. In order to evaluate the performance of cooling methods, physical simulations of cell heating are used to reproduce the thermal profile without the need of a high flux solar simulator or actual cells. Through using resistive heaters built into the same geometry as a CPV module, cooling system designs can be tested achieving similar power distributions as those predicted through multiphysics modeling. Further, the physical model allows for the testing of thermal and solar power limits and performance in a range of non-ideal condition.

Pulsed photoinitiated fabrication of inkjet printed titanium dioxide/reduced graphene oxide nanocomposite thin films

This work reports a new technique for scalable and low-temperature processing of nanostructured TiO2 thin films, allowing for practical manufacturing of TiO2-based devices such as perovskite solar cells at low-temperature or on flexible substrates. Dual layers of dense and mesoporous TiO2/graphitic oxide nanocomposite films are synthesized simultaneously using inkjet printing and pulsed photonic irradiation. Investigation of process parameters including precursor concentration (10-20 wt%) and exposure fluence (4.5-8.5 J cm-2) reveals control over crystalline quality, graphitic oxide phase, film thickness, dendrite density, and optical properties. Raman spectroscopy shows the E g peak, characteristic of anatase phase titania, increases in intensity with higher photonic irradiation fluence, suggesting increased crystallinity through higher fluence processing. Film thickness and dendrite density is shown to increase with precursor concentration in the printed ink. The dense base layer thickness was controlled between 20 and 80 nm. The refractive index of the films is determined by ellipsometry to be 1.92 ± 0.08 at 650 nm. Films exhibit an energy weighted optical transparency of 91.1%, in comparison to 91.3% of a thermally processed film, when in situ carbon materials were removed. Transmission and diffuse reflectance are used to determine optical band gaps of the films ranging from 2.98 to 3.38 eV in accordance with the photonic irradiation fluence and suggests tunability of TiO2 phase composition. The sheet resistance of the synthesized films is measured to be 14.54 ± 1.11 Ω/□ and 28.90 ± 2.24 Ω/□ for films as-processed and after carbon removal, respectively, which is comparable to high temperature processed TiO2 thin films. The studied electrical and optical properties of the light processed films show comparable results to traditionally processed TiO2 while offering the distinct advantages of scalable manufacturing, low-temperature processing, simultaneous bilayer fabrication, and in situ formation of removable carbon nanocomposites.

Optical Design and Validation of an Infrared Transmissive Spectrum Splitting Concentrator Photovoltaic Module

A new modular, hybrid solar power system is designed to generate both electrical and thermal energy by utilizing the full solar spectrum. The key element, an infrared-transparent concentrator photovoltaic (CPV) module, acts as a spectrum splitter, dividing solar radiation into two parts. The ultraviolet and visible light (“in-band”) are converted to electricity with high efficiency in CPV cells, while the infrared light (“out-of-band”) is transmitted directly to a thermal receiver, where thermal power may be converted to electricity by a suitable heat engine or used directly for industrial process heat applications whenever needed. Here, we describe the optical design, modeling, fabrication, and performance validation of this novel spectrum splitting CPV module. A transfer matrix style approach, cumulative transmission model, is built to study the reflection, absorption, and transmission in each layer of the CPV module. To optimize the optical performance, different materials for module superstrate/substrate, encapsulant, cell substrate, and cooling fluids are compared in order to enhance the transmission of out-of-band light through the CPV module by minimizing absorption. Six antireflection coatings along with front and backside electrical contact grids are designed to maximize transmittance of in-band light to the cell and out-of-band light to the thermal receiver. The final design, currently being prototyped, predicts out-of-band light transmission to the thermal receiver of 74.1% (for the passively cooled version) and 65.3% (for the actively cooled version). When epitaxial liftoff technology is applied, the transmission will change to 80.8% (passively cooled) and 71.9% (actively cooled). Experimental prototypes show good agreement with modeled optical performance.