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At least 343 records · Page 19
All sourcesNASA NTRSDOE OSTI
DOE OSTI2018

Influence of Oxygen on the Tribomechanical Properties of Single Crystals of YBa{sub 2}Cu{sub 3}O{sub 7−δ}

This paper reports a study on the mechanical and tribological properties of ab- and a (b) c−planes of YBa{sub 2}Cu{sub 3}O{sub 7−δ} single crystals. The single crystals were grown using a CuO-BaO self-flux method. The oxygenation effect on the mechanical and tribological properties of ab- and a (b) c−planes is reported. For the ab- plane, the hardness and elastic modulus were around 6 and 50 GPa, respectively. In this case, significant differences were not observed among the hardness and elastic modulus at different oxygenation states. However, the hardness and elastic modulus for as-grown and oxygenated YBa{sub 2}Cu{sub 3}O{sub 7−δ} single crystals were different from that of the a (b) c−plane, and were observed to be slightly higher for the as-grown than for the oxygenated samples. For as-grown and oxygenated samples, we observed hardness values around 4.7 and 2.0 GPa, respectively. Regarding the elastic modulus, the values were 75 and 40 GPa, respectively. The indentation fracture toughness values on the ab- plane for the as-grown and oxygenated YBa{sub 2}Cu{sub 3}O{sub 7−δ} single crystal were 3.7 ± 1.2 and 2.9 ± 1.2 MPa m{sup 1/2}, respectively. For the ab- plane, the scratch resistance of the as-grown sample was higher than that of the oxygenated sample and the scratches under load were deeper for the oxygenated sample. As regards the a (b) c−plane, the scar features were seemingly constant through all the scratch lengths and the scratches under load were deeper and larger for the oxygenated than that for the as-grown sample.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2018

Single Crystalline Substrates for III-V Growth via Exfoliation of Bulk Single Crystals

To enable widespread deployment of GaAs PV, the cost of single crystal substrates must be dramatically reduced. Here we present an indium-bonded exfoliation technique that produces substrates for III-V growth by exfoliation of macroscopic single crystals. Beginning with a search of available substrates, we identified several model materials that are lattice matched to III-Vs. Bi 2 Se 3 single crystals were grown via the Bridgman technique in order to demonstrate our exfoliation method. From a centimeter diameter single crystal, up to eleven substrates with RMS roughness of 0.04 nm in a 20x20 micron region were exfoliated using this method. Large area AFM scans determined a terrace length of 72 um between step edges. Thicknesses were determined to range from 40-160 um using cross-sectional SEM. This exfoliation technique opens the door to the widespread study of layered materials as epitaxial substrates.

14 SOLAR ENERGY↗
DOE OSTI2026

Predicting fracture behavior in single crystal nickel using a coupled crystal plasticity phase field damage approach

Understanding the fracture behavior of single crystal metals is critical for predicting material performance under mechanical loading. Here, in this study, we investigate the fracture characteristics of single crystal nickel tensile bars using a crystal plasticity coupled phase field damage (CP-PFD) model. Experimental tensile tests were conducted on 15 specimens spanning five crystallographic orientations and three thickness variants per orientation. The results revealed two distinct fracture modes: brittle fractures with 45-degree angled surfaces and ductile fractures characterized by significant necking. The CP-PFD model successfully replicated these fracture behaviors, demonstrating strong agreement with experimental observations. The model effectively predicted the strain at which necking and fracture occurred, as well as the orientation-dependent fracture mechanisms. By comparing experimental and simulated fracture surfaces, we establish the CP-PFD model as a robust tool for predicting single crystal behavior and damage evolution. This work provides insight into the microstructural dependence of fracture behavior and establishes a predictive framework for modeling orientation-dependent damage evolution in single-crystal nickel.

Crystal plasticity↗
DOE OSTI2013

Investigation of Structure and Crack Formation in Welded Joints of Single Crystal Ni-Base Alloys

Conditions of initiation of hot cracks in welding of single crystal heat-resistant alloys with a 56% content of the γ’-phase were studied. Conditions for providing a polycrystalline structure in HAZ and part of the weld metal were artificially created in one region of a welded joint with the single crystal structure. Welding of the single crystal alloy was performed by the electron beam method in vacuum. Cracks in a low-temperature ductility dip range (ductility dip cracking) were found to form in HAZ and weld of a welded joint with the polycrystalline structure. The nature of cracking of the single crystal weld is related to formation of low-melting point eutectoid interlayers, as well as to exhausting of the safety factor for ductility. In conclusion, cracks in the single crystal weld along the strain grain boundaries are formed by a similar mechanism.

36 MATERIALS SCIENCE↗
NASA NTRS1980

Anisotropy of nickel-base superalloy single crystals

The effects of crystal orientation on the mechanical properties of single crystals of the nickel-based superalloy Mar-M247 are investigated. Tensile tests at temperatures from 23 to 1093 C and stress rupture tests at temperatures from 760 to 1038 C were performed for 52 single crystals at various orientations. During tensile testing between 23 and 760 C, single crystals with high Schmid factors were found to be favorably oriented for slip and to exhibit lower strength and higher ductility than those with low Schmid factors. Crystals which required large rotations to become oriented for cross slip were observed to have the shortest stress rupture lives at 760 C, while those which required little or no rotation had the longest lives. In addition, stereographic triangles obtained for Mar-M247 and Mar-M200 single crystals reveal that crystals with orientations near the -111 had the highest lives, those near the 001 had high lives, and those near the 011 had low lives.

Mackay, R. A.↗
NASA NTRS1986

Method of making macrocrystalline or single crystal semiconductor material

A macrocrystalline or single crystal semiconductive material is formed from a primary substrate including a single crystal or several very large crystals of a relatively low melting material. This primary substrate is deposited on a base such as steel or ceramic, and it may be formed from such metals as zinc, cadmium, germanium, aluminum, tin, lead, copper, brass, magnesium silicide, or magnesium stannide. These materials generally have a melting point below about 1000 C and form on the base crystals the size of fingernails or greater. The primary substrate has an epitaxial relationship with a subsequently applied layer of material, and because of this epitaxial relationship, the material deposited on the primary substrate will have essentially the same crystal size as the crystals in the primary substrate. If required, successive layers are formed, each of a material which has an epitaxial relationship with the previously deposited layer, until a layer is formed which has an epitaxial relationship with the semiconductive material. This layer is referred to as the epitaxial substrate, and its crystals serve as sites for the growth of large crystals of semiconductive material. The primary substrate is passivated to remove or otherwise convert it into a stable or nonreactive state prior to deposition of the seconductive material.

Shlichta, P. J.↗
DOE OSTI2016

Dry-growth of silver single-crystal nanowires from porous Ag structure

A fabrication method of single crystal Ag nanowires in large scale is introduced without any chemical synthesis in wet processes, which usually generates fivefold twinned nanowires of fcc metals. Dense single-crystal nanowires grow on a mechanically polished surface of micro-porous Ag structure, which is created from Ag micro-particles. The diameter and the length of the nanowires can be controlled simply by changing the temperature and the time of the heating during the nanowire growth in air. Unique growth mechanism is described in detail, based on stress-induced migration accelerated by the micro-porous structure where the origin of Ag nanowires growth is incubated. Transmission electron microscopy analysis on the single crystal nanowires is also presented. This simple method offered an alternative preparation for metallic nanowires, especially with the single crystal structure in numerous applications.

36 MATERIALS SCIENCE↗
DOE OSTI2023

Controlled Growth of Single‐Crystal Graphene Wafers on Twin‐Boundary‐Free Cu(111) Substrates

Single-crystal graphene (SCG) wafers are needed to enable mass-electronics and optoelectronics owing to their excellent properties and compatibility with silicon-based technology. Controlled synthesis of high-quality SCG wafers can be done exploiting single-crystal Cu(111) substrates as epitaxial growth substrates recently. However, current Cu(111) films prepared by magnetron sputtering on single-crystal sapphire wafers still suffer from in-plane twin boundaries, which degrade the SCG chemical vapor deposition. Here, in this study, it is shown how to eliminate twin boundaries on Cu and achieve 4 in. Cu(111) wafers with ≈95% crystallinity. The introduction of a temperature gradient on Cu films with designed texture during annealing drives abnormal grain growth across the whole Cu wafer. In-plane twin boundaries are eliminated via migration of out-of-plane grain boundaries. SCG wafers grown on the resulting single-crystal Cu(111) substrates exhibit improved crystallinity with >97% aligned graphene domains. As-synthesized SCG wafers exhibit an average carrier mobility up to 7284 cm 2 V −1 s −1 at room temperature from 103 devices and a uniform sheet resistance with only 5% deviation in 4 in. region.

36 MATERIALS SCIENCE↗
DOE OSTI2016

Hydrothermal Chemistry and Growth of Fergusonite-type RENbO 4 (RE = La–Lu, Y) Single Crystals and New Niobate Hydroxides

A convenient hydrothermal route to high quality single crystals of rare earth orthoniobates RENbO 4 (RE = Y, La–Lu) is discussed. The title compounds can be grown as single crystals in sizes exceeding 2 mm for most of the rare earths using 30 M KOH at temperatures of 700 °C and pressures of 2 kbar. Single crystal X-ray diffraction shows that they all form in the fergusonite structure type, and the structures were solved in space group C 2/ c . Examples based on the largest and smallest rare earth ions in the present study include LaNbO 4 : a = 7.3576(15) Å, b = 11.538(2) Å, c = 5.2128(10) Å, β = 130.900(3)°, Z = 4, R 1 = 0.0162, wR 2 = 0.0405, and LuNbO 4 : a = 6.9805(6) Å, b = 10.8271(8) Å, c = 5.0406(4) Å, β = 131.676(3)°, Z = 4, R 1 = 0.0178, wR 2 = 0.0489. While domain structures are clearly present in the bulk crystals, the domains are much larger than normally reported from high temperature growth methods, and individual single domain crystals on the order of 0.1–1 mm in size can be selected. Rocking curves of these crystals have narrow fwhm and are Gaussian shaped. Several new phases were also isolated as part of the development of the crystal growth chemistry and were characterized by single crystal X-ray diffraction including such examples as K 3 YNb 2 O 7 (OH) 2 : P 6 3 / mmc , a = 5.9770(12) Å, c = 14.901(2) Å, Z = 2, R 1 = 0.0303, wR 2 = 0.0765 and CsNb 2 O 5 (OH): Fd $\bar{3}$ m , a = 10.5869(14) Å, Z = 8, R 1 = 0.0336, wR 2 = 0.0741

36 MATERIALS SCIENCE↗
DOE OSTI2011

Dependence of texture evolution on initial orientation in drawn single crystal copper

The evolution of fiber texture in the drawn single crystal copper wires with initial orientations of < 100>, < 110> and < 111> parallel to axis direction has been studied via electron backscattering diffraction. During cold drawing process, grain subdivision takes place in the < 100>, < 110> and < 111> single crystals. At high strains, a mixture of < 111> and < 100> fiber textures forms, but due to uneven shear strain, the distribution of the < 111> and < 100> fiber textures is inhomogeneous along the radial direction of wires. The < 111> fiber texture component is located in the centre of wires and < 100> is near the surface. Although grain subdivision appears in the < 100>, < 110> and < 111> single crystals, the stability of the three initial orientations is different. The initial orientations of < 100> and < 111> are more stable than < 110>. < 100> is stable at low strains while < 111> becomes stable at high strains. - Research Highlights: {yields} In drawn < 111> and < 100> single crystals, grain subdivision still takes place. {yields} The initial orientations of < 111> and < 100> more stable than < 110>. {yields} < 100> fiber texture located near the surface and < 111> in the centre. {yields} < 100> is stable at low strains but < 111> becomes stable at high strains.

36 MATERIALS SCIENCE↗
DOE OSTI2016

Demonstration of single crystal growth via solid-solid transformation of a glass

Many advanced technologies have relied on the availability of single crystals of appropriate material such as silicon for microelectronics or superalloys for turbine blades. Similarly, many promising materials could unleash their full potential if they were available in a single crystal form. However, the current methods are unsuitable for growing single crystals of these oftentimes incongruently melting, unstable or metastable materials. Here we demonstrate a strategy to overcome this hurdle by avoiding the gaseous or liquid phase, and directly converting glass into a single crystal. Specifically, Sb 2 S 3 single crystals are grown in Sb-S-I glasses as an example of this approach. In this first unambiguous demonstration of an all-solid-state glass → crystal transformation, extraneous nucleation is avoided relative to crystal growth via spatially localized laser heating and inclusion of a suitable glass former in the composition. Lastly, the ability to fabricate patterned single-crystal architecture on a glass surface is demonstrated, providing a new class of micro-structured substrate for low cost epitaxial growth, active planar devices, etc.

36 MATERIALS SCIENCE↗
DOE OSTI2016

Diffraction and single-crystal elastic constants of Inconel 625 at room and elevated temperatures determined by neutron diffraction

In this work, diffraction and single-crystal elastic constants of Inconel 625 have been determined by means of in situ loading at room and elevated temperatures using time-of-flight neutron diffraction. Theoretical models proposed by Voigt, Reuss, and Kroner were used to determine single-crystal elastic constants from measured diffraction elastic constants, with the Kroner model having the best ability to capture experimental data. The magnitude of single-crystal elastic moduli, computed from single-crystal elastic constants, decreases and the single crystal anisotropy increases as temperature increases, indicating the importance of texture in affecting macroscopic stress at elevated temperatures. Finally, the experimental data reported here are of great importance in understanding additive manufacturing of metallic components as: diffraction elastic constants are required for computing residual stresses from residual lattice strains measured using neutron diffraction, which can be used to validate thermomechanical models of additive manufacturing, while single-crystal elastic constants can be used in crystal plasticity modeling, for example, to understand mechanical deformation behavior of additively manufactured components.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Solution growth of single-crystal perovskite structures

A method for growing single-crystal perovskite structures comprises immersing a film of a metal precursor compound on a surface of a substrate, the metal precursor compound comprising a metal ion B, in a solution comprising a cation precursor compound, the cation precursor compound comprising a cation ion A and an anion X, at a concentration of the cation precursor compound, a growth time, and a growth temperature sufficient to dissolve the film to release the metal ion B to form a complex with the anion X and sufficient to induce recrystallization of the complex with the cation ion A to form a plurality of single-crystal perovskite structures composed of A, B and X. The single-crystal perovskite structures, devices incorporating the same, and methods of using the devices are also provided.

36 MATERIALS SCIENCE↗