Gaytan S.M.,University of Texas at El Paso |
Cadena M.,University of Texas at El Paso |
Aldaz M.,University of Texas at El Paso |
Herderick E.,Materials Group |
And 2 more authors.
24th International SFF Symposium - An Additive Manufacturing Conference, SFF 2013
The M-Lab system from ExOne was used to fabricate 3D structures of BaTiO3 ceramic with applications that include dielectric capacitors, sensors, and integrated circuits. For this project, layer thicknesses of 15 and 30 μm and various percentages of binder saturation were used to fabricate components from powder. An organic binding agent was utilized during the printing process and later burned out at ∼600°C prior to sintering. Multiple building parameters and sintering profiles were analyzed and compared in an attempt to obtain dense parts while examining shrinkage percentage variations. Source
Dey C.,Indian Central Glass and Ceramic Research Institute |
Molla A.R.,Indian Central Glass and Ceramic Research Institute |
Goswami M.,Bhabha Atomic Research Center |
Kothiyal G.P.,Materials Group |
Karmakar B.,Indian Central Glass and Ceramic Research Institute
Journal of the Optical Society of America B: Optical Physics
Highly luminescent CdS nanocrystals (NCs) grown in a dielectric (borosilicate glass) matrix have been synthesized by the melt quenching technique.NCsizes are varied by controlling the post thermal treatment durations in the glass matrix and their optical properties have been investigated. The sizes of the CdS NCs calculated from the transmission electron microscopic (TEM) images are found to alter in the range of 4-40 nm. Field emission scanning electron microscopic (FESEM) images reveal the presence of 30-100 nm CdS nanostructures. Photoluminescence (PL) of CdS-glass nanocomposites reveals a sharp green emission peak (~508 nm) due to direct electron-hole recombination along with a broad trap-related emission band. The sharpness, tuning ability of the absorption spectra, and PL covering the visible spectral range are the highest reported to date for any compound semiconductor-dielectric nanocomposite and one single nanocomposite, synthesized by this method, advocating for their potential utilization as functional materials in the fabrication of multiple devices such as luminescent solar concentrators (LSCs), optical color filters, and solid-state lasers. © 2014 Optical Society of America. Source
Debra Fiakas is the Managing Director of , an alternative research resource on small capitalization companies in selected industries. On Friday Rubicon Technology, Inc. RBCN : Nasdaq) announced the appointment of a new chief operating officer to manage the company’s sapphire materials production. Rubicon is a producer of materials used in electronics components, including the company’s specialty, monocrystalline sapphire materials.Rubicon chose a seasoned operator for the COO post, which now encompasses functions previously carried about by managers in two different positions. The new hire, Hany Tamim, was previously with SunEdison SUNE : Nasdaq), the developer and producer of solar cells and modules. He has experience in managing crystal growth and wafer production, two steps Rubicon needs to get right to keep costs low. By elevating these job functions to a position in the corporate suite, Rubicon seems to be signaling a new view on the importance of operational success to the company’s future.Rubicon needs to find its groove, so to speak. The company has experienced a decline in fortunes over the last three and a half years due to what it calls a slump in the market for materials intended for electronics. Rubicon’s products include sapphire core in two to six inch diameter cylinders, patterned sapphire wafers, and sapphire shapes in various sizes. The sapphire cores are sliced for use in Light Emitting Diodes (LED) or as lens covers in mobile devices. Patterned sapphire wafers are also used in LED applications for better efficiency in extracting light. There are additional uses for the company’s sapphire components in electronics destined for the communications, aerospace, and other end markets.Business for Rubicon peaked in 2011, when sales totaled $134.0 million. That was also the last year the company reported a profit. Since then sales have slumped, declining to $33.0 million in the twelve months ending June 2015, and resulting in a net loss of $40.0 million. Operations only required $21.4 million in cash to keep the business going during the last twelve months. Even though the company had $36.0 million in cash on its balance sheet at the end of June 2015, and could potentially support operations for another year, it is understandable why leadership at Rubicon would give Mr. Tamim a shoutout. ‘Help! We need to cut costs so we can survive until the world reawakens to the merits of sapphire materials.’Rubicon has only tangentially benefited from the exit of GT Advanced Technologies GTATQ : OTC/PK) from the sapphire materials sector, following the breakdown of GT’s relationship with Apple, Inc. (APPL: Nasdaq). Apple and GT have differing stories on who was at fault in the demise of Apple’s plans to use sapphire glass on its iWatch and iPhones. The iWatch eventually debuted with sapphire glass components, but iPhone 6 has been produced with conventional glass alternatives. GT Advanced Technologies declared bankruptcy to get away from the toxic sapphire glass production alliance it had with Apple.No one has stepped up to take GT’s mission to bring sapphire any closer to handheld electronic devices than the optical lens components. There is no surprise there. In the end it seemed more a passing dream by Apple engineers and designers, who were not willing to accept the limitations of sapphire crystal growth and the high costs associated with new product development.The benefit Rubicon may have enjoyed from GT’s exit is not in terms of new sales. GT’s former vice president in charge of crystal growth systems development has joined Rubicon as that company’s chief technology officer. So besides Mr. Tamim, Rubicon has a CTO who is also highly sensitive to cost issues in sapphire crystal manufacturing.Rubicon appears to have its back to the wall with continued losses and dwindling cash resources. We have kept the company in the Materials Group of our Mothers of Invention Index of companies that are contributing to energy efficiency because we believe sapphire materials will have a place in 21st century advanced electronics picture. Neither the author of the Small Cap Strategist web log, Crystal Equity Research nor its affiliates have a beneficial interest in the companies mentioned herein. Crystal Equity Research has a Hold recommendation on GTATQ.
Principal research and neutron-scattering instrument scientist Vanessa Peterson has collaborated on a paper just published in Nature Chemistry that reports the discovery of a new torsion spring-like mechanism in a series of coordination frameworks that has implications for the strategic design of future materials with exceptional mechanical properties. The series of materials has the largest linear compressibilities of any crystalline compound, and the volume compressibilities are exceeded only by caesium, rubidium, and xenon. These compressibilities are both exceptionally large and sustained over a broad pressure range spanning at least 1 GPa. The work is the product of a long-standing collaboration with Cameron Kepert at the Molecular Materials Group at the University of Sydney, with the first author Samuel Duyker co-supervised by Kepert and Peterson during his PhD before taking up a postdoctoral position with Peterson, when this work was performed. "Understanding these multifunctional materials with the aim of controlling their range of useful properties is of great interest to the energy industry, but the research brings fundamental knowledge of the atomic and molecular mechanisms, which has broader application" said Peterson. In contrast to the shortening of bonds that occurs in conventional materials, compression in the new series of materials is achieved through structural deformation. The unusual new mechanism was found in a series 'coordination frameworks'—named for the coordinative bonds linking organic molecules and metal atoms. The torsional mechanism is unlike anything seen in any other material, being fundamentally distinct from other compressible frameworks. The team first became interested in the lanthanoid frameworks because of their unusual coordination geometries. "The material is a porous framework, constructed from two types of metals that are connected by cyanide bridging ligands. The coordination environment of the lanthanoid is inherently very unstable, but exists because it is stabilised by the overall framework connectivity." "Near 1 GPa, a change in lattice geometry occurs in the lanthanoid framework through a complex mechanism involving dramatic structural distortion," said Peterson. The LnN units acting like torsion springs are synchronised by rigid Fe(CN)6 units acting like gears. The LnN twists away from its original trigonal prismatic geometry becoming octahedral. These LnN units act as torsional centres that coil dramatically under pressure and enable extreme compressibility in combination with chemical and thermal stability for the first time. "There is competition between two relatively strong effects. A balance is achieved between the significant stored energy in the locally unstable lanthanoid coordination and the opposing force of the hexacyanidoferrate units, which strongly prefer not to change." "These lanthanoid frameworks compress by about 20% in volume at the relatively low pressure of 1 GPa, one of the largest known pressure responses for any crystalline material," said Peterson. This represents a new paradigm in the design of materials with anomalous mechanical behaviours. "There are a range of properties that can be tailored through choice of construction units. Selecting from a range of metal nodes and ligands gives control over the material's porosity, topology, that is, the way that the pores are connected, the chemical functionality, and flexibility of these units." "Because the contribution of each part or unit of the framework to these material properties are known, they can be controlled, and tailored to particular functions. With this knowledge, you can gain insight into how to structurally engineer the properties you want at the molecular level," said Peterson. Of great importance in understanding the details of the compression mechanism in this material series was the validation of computational models using neutron scattering. The combination of the two in this approach is well-known and very powerful. The neutron powder diffraction portion of the research was done on ANSTO's high intensity powder diffractometer, WOMBAT, for which Peterson is an instrument scientist. "The unique properties of neutrons allowed the neutron scattering experiment to be performed on a bulk sample, which was very useful, and provided great contrast in the scattering power of the elements," said Peterson. In earlier work, the team had found that the co-efficient of thermal expansion correlated linearly with the ionic radius of the lanthanoid in this family of materials. As part of the study, they substituted a range of elements, including yttrium, holmium, and lutetium, into the coordination site changing the coordinative bond strength. "We measured the overall property of thermal contraction or expansion using neutron scattering and computational methods to understand the mechanism. We found that there are low energy vibrational modes that give rise to this negative thermal expansion property. One of those modes was extremely unusual," said Peterson. "In theory you can tune the thermal expansion of the material by constructing it with an atom that has an ionic radius that relates to the co-efficient of thermal expansion you desire," explained Peterson. The results of this work were published in Angewandte Chemie in 2013. "We then looked at the possibility of locking in some of these interesting and unusual coordination geometries using chemical substitutions, and we found that by incorporating potassium into the structure, this could indeed be achieved." "The next logical thing to do was to see if we could induce this same coordination geometry change using pressure," said Peterson. When they squashed it, the material underwent the coordination geometry change they were looking for. They compared the compressibility of the material with a range of others, and found that it was extremely compressible —approaching the compressibility of solid polystyrene. They both measured and then calculated the volume change using density functional theory (DFT), for a range of chemically-substituted materials, deriving the compressibility from the change in volume as a function of pressure. "The compressibility changes as different metals are substituted into the unstable coordination geometry. This points towards tunable compressibility which is very desirable." They calculated the framework structure at different pressures to show exactly how the distortion happens and then calculated the contribution of each particular part of the framework in terms of energy—the energy cost of that deformation¬ and the overall contribution to the compressibility. "Basically it's a low energy distortion that relieves the framework strain. We showed that it can be accessed by thermal energy initially in the temperature study." A picture emerges of a torsion spring-like mechanism. Six-coordinate lanthanoid units act like a spring—they flex and distort as the Fe(CN) units act as gears. "The energy cost of deforming the Fe(CN) unit in the framework is very high, so instead it is the lanthanoid unit that deforms," said Peterson. In addition, the lanthanoid framework has sustained axial compression, which is the largest for any crystalline solid in particularly useful regions of .4 to 1.5 GPa. "It occurs via an interesting mechanism," said Peterson "There is a positive linear compressibility that goes through a small region of negative linear compressibility, where as it is squashed it gets smaller really rapidly but then bigger in that direction because of a cam-like action." "We examined quantitatively the energy cost of all of these components to learn exactly what they contribute to the overall volume response of the material to pressure. Once we understand the contribution that each part of the framework has to the overall properties, it can then be tuned." Generally speaking things will try to relieve strain. "Under pressure, the softest part with the lowest energy cost to relieve that pressure will respond." The team suspects that the luminescent properties of these materials are also likely to change upon compression, because the bonding changes so dramatically. "It's very satisfying to find a material with such interesting, useful properties, and then to establish exactly how it is they are achieved," said Peterson. Explore further: The material that's like an octopus More information: Samuel G. Duyker et al. Extreme compressibility in LnFe(CN) coordination framework materials via molecular gears and torsion springs, Nature Chemistry (2016). DOI: 10.1038/nchem.2431
News Article | August 24, 2016
A research group led by Naoki Fukata, a Leader of Nanostructured Semiconducting Materials Group at the International Center for Materials Nanoarchitectonics (MANA), National Institute for Materials Science (NIMS), Japan, and a research group at the Georgia Institute of Technology, US, jointly developed an anode material for lithium (Li)-ion rechargeable batteries by forming nanoparticles made of silicon (Si)-metal composites on metal substrates. The resulting anode material had high capacity—almost twice as high as conventional materials—and a long cycle life. These results will lead to the development of higher-capacity, longer-life anode materials for Li-ion rechargeable batteries.