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CrB is delta Molybdenum Boride structured and crystallizes in the tetragonal I4_1/amd space group. The structure is three-dimensional. Cr3+ is bonded in a 7-coordinate geometry to seven equivalent B3- atoms. There are a spread of Cr–B bond distances ranging from 2.15–2.28 Å. B3- is bonded in a 9-coordinate geometry to seven equivalent Cr3+ and two equivalent B3- atoms. Both B–B bond lengths are 1.77 Å.
HoNiSn2 is delta Molybdenum Boride-derived structured and crystallizes in the orthorhombic Pnma space group. The structure is three-dimensional. there are three inequivalent Ho sites. In the first Ho site, Ho is bonded in a 8-coordinate geometry to six Ni and eight Sn atoms. There are a spread of Ho–Ni bond distances ranging from 3.27–3.50 Å. There are a spread of Ho–Sn bond distances ranging from 3.11–3.19 Å. In the second Ho site, Ho is bonded in a 11-coordinate geometry to two equivalent Ni and nine Sn atoms. Both Ho–Ni bond lengths are 3.05 Å. There are a spread of Ho–Sn bond distances ranging from 3.14–3.51 Å. In the third Ho site, Ho is bonded in a 1-coordinate geometry to four Ni and nine Sn atoms. There are two shorter (3.14 Å) and two longer (3.22 Å) Ho–Ni bond lengths. There are a spread of Ho–Sn bond distances ranging from 3.13–3.58 Å. There are three inequivalent Ni sites. In the first Ni site, Ni is bonded in a 10-coordinate geometry to five Ho and five Sn atoms. There are a spread of Ni–Sn bond distances ranging from 2.55–2.75 Å. In the second Ni site, Ni is bonded in a 7-coordinate geometry to three Ho and five Sn atoms. There are a spread of Ni–Sn bond distances ranging from 2.49–2.79 Å. In the third Ni site, Ni is bonded in a 10-coordinate geometry to four Ho and five Sn atoms. There are a spread of Ni–Sn bond distances ranging from 2.54–2.69 Å. There are six inequivalent Sn sites. In the first Sn site, Sn is bonded in a 8-coordinate geometry to four Ho, three equivalent Ni, and one Sn atom. The Sn–Sn bond length is 3.01 Å. In the second Sn site, Sn is bonded in a 9-coordinate geometry to six Ho and three Ni atoms. In the third Sn site, Sn is bonded in a 6-coordinate geometry to four Ho and two Ni atoms. In the fourth Sn site, Sn is bonded in a 7-coordinate geometry to four Ho and three Ni atoms. In the fifth Sn site, Sn is bonded in a 8-coordinate geometry to four Ho, three Ni, and one Sn atom. In the sixth Sn site, Sn is bonded in a 2-coordinate geometry to four Ho and one Ni atom.
Pr2AlSi is delta Molybdenum Boride-derived structured and crystallizes in the orthorhombic Amm2 space group. The structure is three-dimensional. there are two inequivalent Pr sites. In the first Pr site, Pr is bonded in a 7-coordinate geometry to three equivalent Al and four equivalent Si atoms. There are two shorter (3.27 Å) and one longer (3.35 Å) Pr–Al bond lengths. All Pr–Si bond lengths are 3.16 Å. In the second Pr site, Pr is bonded in a 7-coordinate geometry to four equivalent Al and three equivalent Si atoms. All Pr–Al bond lengths are 3.17 Å. There are one shorter (3.28 Å) and two longer (3.32 Å) Pr–Si bond lengths. Al is bonded in a 2-coordinate geometry to seven Pr and two equivalent Si atoms. Both Al–Si bond lengths are 2.57 Å. Si is bonded in a 9-coordinate geometry to seven Pr and two equivalent Al atoms.
TbNiSn2 is delta Molybdenum Boride-derived structured and crystallizes in the orthorhombic Pnma space group. The structure is three-dimensional. there are three inequivalent Tb sites. In the first Tb site, Tb is bonded in a 8-coordinate geometry to six Ni and eight Sn atoms. There are a spread of Tb–Ni bond distances ranging from 3.30–3.48 Å. There are a spread of Tb–Sn bond distances ranging from 3.13–3.20 Å. In the second Tb site, Tb is bonded in a 11-coordinate geometry to three Ni and nine Sn atoms. There are two shorter (3.09 Å) and one longer (3.53 Å) Tb–Ni bond lengths. There are a spread of Tb–Sn bond distances ranging from 3.16–3.52 Å. In the third Tb site, Tb is bonded in a 1-coordinate geometry to four Ni and nine Sn atoms. There are two shorter (3.16 Å) and two longer (3.26 Å) Tb–Ni bond lengths. There are a spread of Tb–Sn bond distances ranging from 3.16–3.59 Å. There are three inequivalent Ni sites. In the first Ni site, Ni is bonded in a 10-coordinate geometry to five Tb and five Sn atoms. There are a spread of Ni–Sn bond distances ranging from 2.55–2.76 Å. In the second Ni site, Ni is bonded in a 7-coordinate geometry to three Tb and five Sn atoms. There are a spread of Ni–Sn bond distances ranging from 2.51–2.79 Å. In the third Ni site, Ni is bonded in a 10-coordinate geometry to five Tb and five Sn atoms. There are a spread of Ni–Sn bond distances ranging from 2.53–2.68 Å. There are six inequivalent Sn sites. In the first Sn site, Sn is bonded in a 8-coordinate geometry to four Tb, three equivalent Ni, and one Sn atom. The Sn–Sn bond length is 3.03 Å. In the second Sn site, Sn is bonded in a 9-coordinate geometry to six Tb and three Ni atoms. In the third Sn site, Sn is bonded in a 6-coordinate geometry to four Tb and two Ni atoms. In the fourth Sn site, Sn is bonded in a 7-coordinate geometry to four Tb and three Ni atoms. In the fifth Sn site, Sn is bonded in a 8-coordinate geometry to four Tb, three Ni, and one Sn atom. In the sixth Sn site, Sn is bonded in a 2-coordinate geometry to four Tb and one Ni atom.
TmPd2Ge is delta Molybdenum Boride-derived structured and crystallizes in the orthorhombic Pnma space group. The structure is three-dimensional. Tm is bonded in a 11-coordinate geometry to eight equivalent Pd and three equivalent Ge atoms. There are a spread of Tm–Pd bond distances ranging from 3.03–3.13 Å. There are a spread of Tm–Ge bond distances ranging from 2.96–3.03 Å. Pd is bonded in a 7-coordinate geometry to four equivalent Tm and three equivalent Ge atoms. There are a spread of Pd–Ge bond distances ranging from 2.52–2.65 Å. Ge is bonded in a 9-coordinate geometry to three equivalent Tm and six equivalent Pd atoms.
Mg3Si4 is delta Molybdenum Boride-like structured and crystallizes in the triclinic P-1 space group. The structure is three-dimensional. there are three inequivalent Mg sites. In the first Mg site, Mg is bonded in a 7-coordinate geometry to seven Si atoms. There are a spread of Mg–Si bond distances ranging from 2.78–2.98 Å. In the second Mg site, Mg is bonded in a 1-coordinate geometry to eight Si atoms. There are a spread of Mg–Si bond distances ranging from 2.81–3.15 Å. In the third Mg site, Mg is bonded in a 6-coordinate geometry to six Si atoms. There are a spread of Mg–Si bond distances ranging from 2.73–2.94 Å. There are four inequivalent Si sites. In the first Si site, Si is bonded in a 9-coordinate geometry to five Mg and four Si atoms. There are a spread of Si–Si bond distances ranging from 2.43–2.67 Å. In the second Si site, Si is bonded in a 9-coordinate geometry to five Mg and four Si atoms. The Si–Si bond length is 2.55 Å. In the third Si site, Si is bonded in a 9-coordinate geometry to six Mg and three Si atoms. There are one shorter (2.56 Å) and one longer (2.57 Å) Si–Si bond lengths. In the fourth Si site, Si is bonded in a 10-coordinate geometry to five Mg and three Si atoms.
Mg5Si6 is delta Molybdenum Boride-like structured and crystallizes in the triclinic P1 space group. The structure is three-dimensional. there are ten inequivalent Mg sites. In the first Mg site, Mg is bonded in a 5-coordinate geometry to five Si atoms. There are a spread of Mg–Si bond distances ranging from 2.82–3.06 Å. In the second Mg site, Mg is bonded in a 6-coordinate geometry to six Si atoms. There are a spread of Mg–Si bond distances ranging from 2.72–2.96 Å. In the third Mg site, Mg is bonded in a 6-coordinate geometry to eight Si atoms. There are a spread of Mg–Si bond distances ranging from 2.70–3.13 Å. In the fourth Mg site, Mg is bonded in a 3-coordinate geometry to seven Si atoms. There are a spread of Mg–Si bond distances ranging from 2.63–3.07 Å. In the fifth Mg site, Mg is bonded in a 4-coordinate geometry to six Si atoms. There are a spread of Mg–Si bond distances ranging from 2.70–3.11 Å. In the sixth Mg site, Mg is bonded in a 7-coordinate geometry to seven Si atoms. There are a spread of Mg–Si bond distances ranging from 2.79–3.10 Å. In the seventh Mg site, Mg is bonded in a 6-coordinate geometry to eight Si atoms. There are a spread of Mg–Si bond distances ranging from 2.84–3.21 Å. In the eighth Mg site, Mg is bonded in a 3-coordinate geometry to nine Si atoms. There are a spread of Mg–Si bond distances ranging from 2.75–3.09 Å. In the ninth Mg site, Mg is bonded in a 6-coordinate geometry to six Si atoms. There are a spread of Mg–Si bond distances ranging from 2.80–2.96 Å. In the tenth Mg site, Mg is bonded in a 12-coordinate geometry to seven Si atoms. There are a spread of Mg–Si bond distances ranging from 2.74–2.96 Å. There are twelve inequivalent Si sites. In the first Si site, Si is bonded in a 9-coordinate geometry to seven Mg and two Si atoms. There are one shorter (2.48 Å) and one longer (2.53 Å) Si–Si bond lengths. In the second Si site, Si is bonded in a 6-coordinate geometry to four Mg and two Si atoms. The Si–Si bond length is 2.39 Å. In the third Si site, Si is bonded in a 9-coordinate geometry to five Mg and four Si atoms. There are a spread of Si–Si bond distances ranging from 2.58–2.75 Å. In the fourth Si site, Si is bonded in a 10-coordinate geometry to five Mg and five Si atoms. There are a spread of Si–Si bond distances ranging from 2.40–2.76 Å. In the fifth Si site, Si is bonded in a 9-coordinate geometry to six Mg and three Si atoms. There are a spread of Si–Si bond distances ranging from 2.46–2.59 Å. In the sixth Si site, Si is bonded in a 9-coordinate geometry to seven Mg and two Si atoms. There are one shorter (2.34 Å) and one longer (2.48 Å) Si–Si bond lengths. In the seventh Si site, Si is bonded in a 9-coordinate geometry to seven Mg and two Si atoms. The Si–Si bond length is 2.40 Å. In the eighth Si site, Si is bonded in a 9-coordinate geometry to six Mg and three Si atoms. The Si–Si bond length is 2.48 Å. In the ninth Si site, Si is bonded in a 6-coordinate geometry to four Mg and two Si atoms. In the tenth Si site, Si is bonded in a 9-coordinate geometry to six Mg and three Si atoms. In the eleventh Si site, Si is bonded in a 11-coordinate geometry to seven Mg and four Si atoms. In the twelfth Si site, Si is bonded in a 7-coordinate geometry to five Mg and two equivalent Si atoms.
Sr7Ge6 is delta Molybdenum Boride-like structured and crystallizes in the orthorhombic Pnma space group. The structure is three-dimensional. there are four inequivalent Sr sites. In the first Sr site, Sr is bonded in a 6-coordinate geometry to six Ge atoms. There are a spread of Sr–Ge bond distances ranging from 3.20–3.34 Å. In the second Sr site, Sr is bonded in a 7-coordinate geometry to seven Ge atoms. There are a spread of Sr–Ge bond distances ranging from 3.34–3.77 Å. In the third Sr site, Sr is bonded in a 7-coordinate geometry to seven Ge atoms. There are a spread of Sr–Ge bond distances ranging from 3.24–3.62 Å. In the fourth Sr site, Sr is bonded in a 3-coordinate geometry to five Ge atoms. There are a spread of Sr–Ge bond distances ranging from 3.12–3.67 Å. There are four inequivalent Ge sites. In the first Ge site, Ge is bonded in a 9-coordinate geometry to eight Sr and one Ge atom. The Ge–Ge bond length is 2.62 Å. In the second Ge site, Ge is bonded in a 5-coordinate geometry to seven Sr and one Ge atom. The Ge–Ge bond length is 2.55 Å. In the third Ge site, Ge is bonded in a 9-coordinate geometry to eight Sr and one Ge atom. In the fourth Ge site, Ge is bonded in a 9-coordinate geometry to seven Sr and two Ge atoms. The Ge–Ge bond length is 2.57 Å.
Dy2CuGa3 is Tungsten boride-derived structured and crystallizes in the trigonal P3m1 space group. The structure is three-dimensional. there are two inequivalent Dy sites. In the first Dy site, Dy is bonded in a 12-coordinate geometry to three equivalent Cu and nine Ga atoms. All Dy–Cu bond lengths are 2.89 Å. There are a spread of Dy–Ga bond distances ranging from 2.98–3.39 Å. In the second Dy site, Dy is bonded in a 12-coordinate geometry to three equivalent Cu and nine Ga atoms. All Dy–Cu bond lengths are 3.21 Å. There are six shorter (2.96 Å) and three longer (3.37 Å) Dy–Ga bond lengths. Cu is bonded in a 10-coordinate geometry to six Dy and four Ga atoms. There are three shorter (2.56 Å) and one longer (2.98 Å) Cu–Ga bond lengths. There are three inequivalent Ga sites. In the first Ga site, Ga is bonded in a 9-coordinate geometry to six Dy, three equivalent Cu, and one Ga atom. The Ga–Ga bond length is 3.09 Å. In the second Ga site, Ga is bonded in a 10-coordinate geometry to six Dy and four Ga atoms. All Ga–Ga bond lengths are 2.61 Å. In the third Ga site, Ga is bonded in a 10-coordinate geometry to six Dy, one Cu, and three equivalent Ga atoms.
Fine powders of (Hf1-xZrx)B2 solid solution were synthesized by two methods. In the first one, solution-based processing of HfCl4, ZrCl4, sucrose and H3BO3 was carried out followed by heat treatment (e.g., at 1500 °C for 1 h) in Argon to achieve the carbothermal reduction (CTR) reaction to form the boride solid solution. In the second one, called boron hydride reduction (BHR) method, HfCl4, ZrCl4 and NaBH4 were directly mixed in a glove box followed by heat treatment in Argon at elevated temperatures from 700 to 1500 °C. In addition, the powders synthesized via both methods were flash sintered without sample preheating in a homemade setup. The synthesized powders as well as the flash sintered bulk ceramics were characterized using different techniques including XRD, SEM, EDS, TEM, TGA-DSC, and Vickers hardness test to reveal the inter-relationships between starting materials composition, processing conditions, and the resulting materials microstructure and physical/chemical properties.
Ultra-high temperature ceramic materials (UHTCs) are important for designing high-performance aerospace vehicles that can withstand repeated exposures to high temperatures. UHTCs mixed with silicides often have well-controlled oxidation due to the formation of protective silicates, which create a regenerative outer protective layer. Borides are known to have high melting points, high hardness and reasonably good oxidation resistance. In this study, Hf 0.75 Ta 0.25 B 2 (HTB) is proposed as a potential alternative to YSZ protective coatings and ZrB 2- SiC composites via the formation of Hf 6 Ta 2 O 17 (HTO) passivation layer. The objective of this paper is to explore the parameter space of HTB synthesis via borocarbothermal (BCTR). Effects on particle size, phase purity, and residual oxygen content were analyzed with parameters of atmosphere composition, reactant grain sizes, and differing reaction pathways. The BCTR of HfO 2 and Ta 2 O 5 were analyzed to predict HTB behavior. It was shown that both one-step and two-step reaction routes can yield HTB, but two-step yields a purer product. Nano B 4 C produced finer HTB and facilitated reaction completion. Using a reducing atmosphere also enhanced reaction completion
Non-oxide ceramics, which consist of predominantly carbides, borides, and nitrides, are of great interest to modern engineering because of their resistance to extreme conditions. Properties of such materials include high temperature resistance, high hardness, chemical resistance, and high fracture toughness. However, the main method for manufacturing parts of these materials is by machining cylindrical billets to the desired geometry. Not only does this produce waste, but the cost of machining is high since the part materials are of such high hardness. This method is used because these non-oxide ceramics must be sintered to high density using simultaneous heat and pressure within a hot-pressing unit. These units are inherently restricted to cylindrical geometries. A proposed way to expand the capabilities of a hot-press is by using intermediate compressible dies. This method consists of surrounding a ceramic part green body with a material that will shrink at the same rate as the part and survive the hot-pressing conditions. At the end, the compressible die material would be removed leaving a nearly net shaped hot-pressed part. In this study, graphite powder was investigated as the compressible die material with its shrinkage rate being controlled by particle size mixing. Both ceramic materials and graphite were then cast into parts and compressible dies respectively to show the feasibility of the compressible die hot-pressing method.
Project Goal and Objective. The demand for energy and for an upgraded energy infrastructure has steadily grown, as have the needs for energy independence and alternatives to our reliance on petroleum. Hydrogen is considered the most viable fuels for wide-scale implementation in the near future as it is less-polluting, non-toxic, and has more stored energy than petroleum. It is envisioned that hydrogen can eventually become the prime energy carrier, integrating the transportation, grid, and chemical sectors in a way that improves resiliency, diversifies feedstocks, and affords new economic opportunities. A key remaining challenge is the development materials with enhanced gravimetric and volumetric hydrogen storage capacities that offer a higher performance than compressed gas. These materials would eliminate the need for large-scale compression, thereby dramatically reducing the footprint and cost of gas storage. The high gravimetric and volumetric hydrogen capacities of complex hydrides has prompted an intensive investigation of the potential of this class of materials as hydrogen storage media over the past 25 years. Among the many complex hydrides that have been explored, magnesium borohydride, Mg(BH 4 ) 2 , has been found to possess the best combination of practical thermodynamic properties. These include a gravimetric H 2 density of 14.9 wt% H 2 and thermodynamics for the dehydrogenation of Mg(BH 4 ) 2 to MgB 2 (equation 1) (ΔH° = 39 kJ/mol H 2 , ΔS = 112 J/K mol H 2 ) which lie in the narrow window required Mg(BH 4 ) 2 $\Leftrightarrow$ MgB 2 + 4 H 2 (1) for reversibility under moderate pressure and temperature. However, overcoming the extremely slow kinetics of the reversible release of hydrogen by this material in the solid state is a daunting challenge. At temperatures greater than 400 °C, the borohydride releases up to 14 wt% hydrogen giving MgB 2 . We discovered that the direct re-hydrogenation of MgB 2 to Mg(BH 4 ) 2 can be accomplished under 950 bar H 2 at 400 °C. While this demonstrated that complete reversibility can be achieved, the conditions employed are far too extreme for commercial hydrogen storage applications. More recently, we found through US DOE funded research projects (EERE HyMARC and HySCOR), that hydrogen cycling, can be accomplish at much milder conditions upon modification of the borohydride or boride. Guided by these discoveries these discoveries, the objective of this research project was to obtain key information that will enable the development of a model of reversible hydrogenation of MgB 2 to Mg(BH 4 ) 2 . The ultimate goal of our efforts is to attain a model of this transformation that can be utilized to accelerate development further advanced materials. This project directly follows on discoveries that were made over the course of a US DOE, EERE HyMARC project that was focused on improvement of the hydrogen cycling kinetics of modified MgB 2 . We found that that mechanical milling with graphene results the desired, pronounced kinetic enhancement. The dramatic lowering of the conditions required for the hydrogenation of MgB 2 is a significant step towards overcoming its chemical inertness allowing its development as a practical onboard hydrogen storage material. However, the exact nature of the modification(s) of MgB 2 that is responsible for its activation towards hydrogenation is completely unknown. This situation is not unique, as efforts to develop hydrogen storage materials typically have a narrow focus rather than a comprehensive approach that takes atomic level bonding and structure; molecular dynamics; long range, nano- and mesoscale-structure and their interconnection all into account. The goal of this project was the development of a comprehensive, multi-scale computational model of reversible hydrogenation of MgB 2 to Mg(BH 4 ) 2 that can be utilized for development of higher performance versions of the modified material. Development of the model requires determination of: 1) the bulk, nano-scale, and meso-scale structural changes occurring at elevated pressure following mechano-chemical modification of MgB 2 ; 2) the reaction pathway of the reversible hydrogenation of MgB 2 to Mg(BH 4 ) 2 ; 3) the effect of elevated pressure and mechano-chemical modification on the chemical reaction pathways; 4) the interactions at solid-gas interfaces; and particle surfaces; and 5) the kinetics and thermodynamic parameters associated with each step of the hydrogenation reaction pathway. This investigation required advanced techniques as preliminary, standard XRD, 11 B NMR, and FTIR analysis showed no signs of material modification. In order to gain this level of understanding of modified MgB 2 , required the teaming of a diverse group of experts and state-of-the art experimental capabilities at the University of Hawaii at Manoa (UHM) and collaborating National Laboratories: Craig Jensen , Department of Chemistry (PI and Project Director), solid state, solution, and high pressure NMR spectroscopy; solid-state synthesis; and high pressure hydrogenation (collaboration with SNL); Godwin Severa , Hawaii Natural Energy Institute (co-PI) calorimetry; infrared and Raman spectroscopy (collaboration with NREL); Dera , high pressure X-ray diffraction including in situ experiments (collaboration with ANL); Hope Ishii , Hawaii Institute of Geophysics electron microscopy investigations (collaboration with LBNL); and Joe Brown , Mechanical Engineering , material electronic structure and electric field effects.
A boron-rich boron–carbide material (B4+δC) was synthesized by spark plasma sintering of a ball-milled mixture of high-purity boron powder and graphitic carbon at a pressure of 7 MPa and a temperature of 1930 °C. This high-pressure, high-temperature synthesized material was recovered and characterized by X-ray diffraction, X-ray photoelectron spectroscopy, Raman spectroscopy, Vickers hardness measurements, and thermal oxidation studies. The X-ray diffraction studies revealed a single-phase rhombohedral structure (space group R-3m) with lattice parameters in hexagonal representation as a = 5.609 ± 0.007 Å and c = 12.082 ± 0.02 Å. The experimental lattice parameters result in a value of δ = 0.55, or the composition of the synthesized compound as B4.55C. The high-resolution scans of boron binding energy reveal the existence of a B-C bond at 188.5 eV. Raman spectroscopy reveals the existence of a 386 cm−1 vibrational mode representative of C-B-B linear chain formation due to excess boron in the lattice. The measured Vickers microhardness at a load of 200 gf shows a high hardness value of 33.8 ± 2.3 GPa. Thermal gravimetric studies on B4.55C were conducted at a temperature of 1300 °C in a compressed dry air environment, and its behavior is compared to other high-temperature ceramic materials such as high-entropy transition metal boride. The high neutron absorption cross section, high melting point, high mechanical strength, and thermal oxidation resistance make this material ideal for applications in extreme environments.
A non-stoichiometric nanocomposite coating and method of making and using the coating. The non-stoichiometric nanocomposite coating is disposed on a base material, such as a metal or ceramic; and the nanocomposite consists essentially of a matrix of an alloy selected from the group of Cu, Ni, Pd, Pt and Re which are catalytically active for cracking of carbon bonds in oils and greases and a grain structure selected from the group of borides, carbides and nitrides.
Power electronics materials are poised to play a critical role in fulfilling next generation energy needs, with up to 90% of future energy demand predicted to flow through power electronics at some point.[1] Among a number of candidate materials, AlxGa1-xN is the strongest, having bipolar dopability, thermal and chemical stability, an ultra-wide bandgap, and demonstrated experimental feasibility. However, AlGaN growth is limited by a lack of lattice-matched substrates, ultimately stunting material quality at higher thicknesses needed for power electronics applications. Further, high power applications increasingly call for fully vertical device structures, necessitating a conductive substrate. [1] Recently our group identified the (111) plane of TaC as a conductive surface lattice-matched to Al0.55Ga0.45N, taking inspiration from prior work of AlN and GaN binaries on carbide and boride substrates. [2,3,4] In this talk we demonstrate the growth of (111)-oriented TaC by RF sputtering. We investigate the interface of TaC with sapphire and SiC substrates and identify means to suppress competing Ta2C nucleation in order to stabilize (111)-oriented TaC. Potential stacking sequences are identified with respect to crystal structure and observed twinning in the TaC films. We next assess structural changes and film recrystallization that results from face-to-face annealing of TaC thin films at high temperatures above 1500 degrees Celsius. Changes to grain structure and domain size are assessed by x-ray diffraction and surface morphology is explored using atomic force microscopy. Figure 1 shows significant improvements to in- and out-of-plane strain following annealing along with the formation of terraced step edges at the film surface. Strain as a function of material composition and thickness is considered, as this may play a major role in future nucleation of AlGaN layers.
A carbon fiber composite material comprising: (i) a carbon fiber having an outer surface, a thickness of at least 1 micron, and an aspect ratio of at least 1000; (ii) a sizing agent coated on the outer surface of the carbon fiber, wherein the sizing agent has a thickness of up to 200 nm; and (iii) nanoparticles having a size in at least one dimension of up to 100 nm embedded within the sizing agent, wherein the nanoparticles have a metal carbide, metal oxide, metal nitride, and/or metal boride composition. A method for producing the fiber composite material comprises: (a) continuously feeding and coating a continuous carbon fiber with a liquid containing a solvent, sizing agent, and nanoparticles in a continuous feed-through process to result in said sizing agent and nanoparticles coating the surface of the continuous carbon fiber; and (b) removing the solvent from the coated fiber.
Power electronics materials are poised to play a critical role in fulfilling next generation energy needs, with up to 90% of future energy demand predicted to flow through power electronics at some point. AlxGa1-xN ranks high among candidate materials, having bipolar dopability, thermal and chemical stability and an ultra-wide bandgap. However, AlGaN growth is limited by a lack of lattice-matched substrates, ultimately stunting material quality at higher thicknesses needed for power electronics applications. Further, high power applications increasingly call for fully vertical device structures, necessitating a conductive substrate. Recently our group identified the (111) plane of TaC as a conductive surface lattice-matched to Al0.55Ga0.45N, taking inspiration from prior work of AlN and GaN binaries on carbide and boride substrates. In this talk we demonstrate the growth of (111)-oriented TaC by RF sputtering. We investigate the interface of TaC with sapphire and SiC substrates and identify means to suppress competing Ta2C nucleation in order to stabilize (111)-oriented TaC. Potential stacking sequences are identified with respect to crystal structure and observed twinning in the TaC films. We next assess structural changes and film recrystallization that results from face-to-face annealing of TaC thin films at high temperatures above 1500 degrees C. Changes to grain structure and domain size are assessed by x-ray diffraction and surface morphology is explored using atomic force microscopy. Figure 1 shows significant improvements to in- and out-of-plane strain following annealing along with the formation of terraced step edges at the film surface. Strain as a function of material composition and thickness is considered, as this may play a major role in future nucleation of AlGaN layers. (1) R. J. in a face-to-face configuration, as illustrated in the schematic at left. Kaplar et al 2017, ECS J. Solid State Sci. Technol. 6 Q3061; (2) D. M. Roberts et al 2022, https://arxiv.org/abs/2208.11769; (3) T. Aizawa et al 2008, J Crys Growth 310, 1 22; (4) R. Liu et al 2002, Appl. Phys. Lett. 81, 3182-3184.