Research on low voltage electroluminescent devices with storage, phase 2 Final technical report
Development of monocrystals and formation of electroluminescent p-n junctions
Hanlet, J. M.↗
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X-ray diffraction identification of minerals in lunar regolith returned by Luna 16 automatic station
The methods of powder and monocrystal X-ray diffraction served in identifying the mineral composition of gross samples of regolith from different levels of the drill core and about 80 individual regolith particles returned by the Luna 16 station. It was established that the Sea of Fertility regolith includes pyroxenes of the augite-pigeonite series, anorthites, ilmenite, olivines, spinels, alpha cristobalite, iron particles, glass, and several as yet unidentified particles. Crystallographic and roentgenometric data are given for all the lunar minerals found.
Makarov, Y. S.↗
Germanium-silicon solid solutions
An experiment on melting and directional crystallization of an antimony (Sb) doped germanium silicon (GeSi) solid solution was designed for the Apollo-Soyuz Test Project (ASTP) to study the possibility of using zero-g conditions for obtaining solid-solution monocrystals with uniformly distributed components. Crystallization in the zero-g environment did not occur under ideal stationary growth and segregation conditions. Crystallization under zero-g conditions revealed the heterogeneous nature of Si and Sb distribution in the cross sections of crystals. The presence of the radial thermal gradient in the multipurpose furnace could be one of the reasons for such Si and Sb distribution. The structure of space-grown crystals correlates with the nature of heterogeneities of Si and Sb distribution in crystals. The type of surface morphology and the contour observed in space-grown crystals were never observed in ground-based crystals and indicate the absence of wetting of the graphitized walls of the ampoule by the melt during melting and crystallization.
Zemskov, V. S.↗
Materials for advanced turbine engines. Volume 1: Advanced blade tip seal system
Project 3, the subject of this technical report, was structured toward the successful engine demonstration of an improved-efficiency, long-life, tip-seal system for turbine blades. The advanced tip-seal system was designed to maintain close operating clearances between turbine blade tips and turbine shrouds and, at the same time, be resistant to environmental effects including high-temperature oxidation, hot corrosion, and thermal cycling. The turbine blade tip comprised an environmentally resistant, activated-diffussion-bonded, monocrystal superalloy combined with a thin layer of aluminium oxide abrasive particles entrapped in an electroplated NiCr matrix. The project established the tip design and joint location, characterized the single-crystal tip alloy and abrasive tip treatment, and established the manufacturing and quality-control plans required to fully process the blades. A total of 171 blades were fully manufactured, and 100 were endurance and performance engine-tested.
Zelahy, J. W.↗
Multifrequency dial sensing of the atmospheric gaseous constituents using the first and second harmonics of a tunable CO2 laser radiation
The results of field measurements of concentration of some gaseous components of the atmosphere along the paths, in Sofia, Bulgaria, using a gas analyzer based on the use of a CO2 laser radiation frequency-doubled with ZnGeP2 monocrystals are presented. The gas analyzer is a traditional long path absorption meter. Radiation from the tunable CO2 laser of low pressure and from an additional He-Ne laser is directed to a colliminating hundredfold Gregori telescope with a 300 mm diameter of the principal mirror. The dimensions of the mirrors of a retroreflector 500 x 500 mm and a receiving telescope allow one to totally intercept the beam passed through the atmospheric layer under study and back.
Zuev, V. E.↗
Heat's on to develop high-temperature materials
An evaluation is made of the state-of-the-art and foreseeable development prospects in high temperature engineering materials applicable to advanced heat engines and other aerothermodynamically affected structures. Attention is given to monocrystal- and microcrystal-producing metal solidification processes, soft oxide and chemically stable fluoride high temperature solid lubricants, polyimide and other high temperature polymers for propulsion system applications, high strength/toughness ceramics for heat engine structural components, thermal barrier coatings, and metal-matrix composites employing refractory matrices as well as reinforcing fibers.
Gray, Hugh R.↗
Structure-property relationships in directionally solidified single crystal NiAl
The ordered intermetallic alloy NiAl is being considered as a potential high temperature structural material, but lack of ductility at ambient temperatures, especially in polycrystalline form, is presently a major obstacle in achieving this goal. Even general agreement of the intrinsic ductility that can be achieved in monocrystals is in dispute. In order to understand this problem, two directionally solidified ingots of NiAl which displayed known differences in ductility were characterized in sufficient detail to identify the corresponding microstructural differences. It was found that the type and size of casting defects, i.e., porosity, present in the material were the major factors in controlling ductility of NiAl single crystals and could explain the order of magnitude variance in fracture strains reported in the literature.
Noebe, R. D.↗
Cryogenic monocrystalline silicon Fabry-Perot cavity for the stabilization of laser frequency
A 1.6 kg silicon monocrystal was used to make a Fabry-Perot optical cavity operated at cryogenic temperatures. High-resolution thermal expansion measurements were made as the silicon cooled to 4.2 K, in order to characterize the cavity as a length reference standard. A helium-neon laser was then locked to a transmission resonance at liquid-helium temperatures, and the laser frequency tracked the cavity resonance with error fluctuations at the level of 10 Hz/sq rt Hz in the bandwidth dc to 1 Hz. Implications of the combined set of data, thermal expansion plus frequency-tracking fluctuations, for using such a system as a frequency standard are discussed.
Richard, J.-P.↗
Primary Dendrite Array Morphology: Observations from Ground-based and Space Station Processed Samples
Influence of natural convection on primary dendrite array morphology during directional solidification is being investigated under a collaborative European Space Agency-NASA joint research program, "Microstructure Formation in Castings of Technical Alloys under Diffusive and Magnetically Controlled Convective Conditions (MICAST)". Two Aluminum-7 wt pct Silicon alloy samples, MICAST6 and MICAST7, were directionally solidified in microgravity on the International Space Station. Terrestrially grown dendritic monocrystal cylindrical samples were remelted and directionally solidified at 18 K/cm (MICAST6) and 28 K/cm (MICAST7). Directional solidification involved a growth speed step increase (MICAST6-from 5 to 50 micron/s) and a speed decrease (MICAST7-from 20 to 10 micron/s). Distribution and morphology of primary dendrites is currently being characterized in these samples, and also in samples solidified on earth under nominally similar thermal gradients and growth speeds. Primary dendrite spacing and trunk diameter measurements from this investigation will be presented.
Tewari, Surendra↗
Primary Dendrite Array: Observations from Ground-Based and Space Station Processed Samples
Influence of natural convection on primary dendrite array morphology during directional solidification is being investigated under a collaborative European Space Agency-NASA joint research program, Microstructure Formation in Castings of Technical Alloys under Diffusive and Magnetically Controlled Convective Conditions (MICAST). Two Aluminum-7 wt pct Silicon alloy samples, MICAST6 and MICAST7, were directionally solidified in microgravity on the International Space Station. Terrestrially grown dendritic monocrystal cylindrical samples were remelted and directionally solidified at 18 K per centimeter (MICAST6) and 28 K per centimeter (MICAST7). Directional solidification involved a growth speed step increase (MICAST6-from 5 to 50 millimeters per second) and a speed decrease (MICAST7-from 20 to 10 millimeters per second). Distribution and morphology of primary dendrites is currently being characterized in these samples, and also in samples solidified on earth under nominally similar thermal gradients and growth speeds. Primary dendrite spacing and trunk diameter measurements from this investigation will be presented.
Tewari, Surendra N.↗
Structure and Optical Properties Of LiNbO{sub 3}:В Crystals Grown from Charges of Different Origins
It was shown that, without entering the structure of the crystal, boron can change the structure of the melt and have a significant effect on the fine features of the structure and the physical characteristics of lithium niobate crystals. Crystals grown from a charge doped with boron by the direct solid-phase method have a stronger photorefractive effect and a smaller forbidden band width than crystals grown from the re-extract doped homogeneously with boron at the niobium pentoxide extraction stage.
36 MATERIALS SCIENCE↗
Pinning-Induced Vortex-System Disordering at the Origin of the Second Magnetization Peak in Superconducting Single Crystals
The nature of the second magnetization peak (SMP) appearing on the dc magnetic hysteresis curves of superconducting single crystals with random pinning is still under debate. Many interesting SMP models and mechanisms were proposed and considered so far, and it is believed at present that this effect is system dependent. We analyzed the dc magnetization curves and the magnetic relaxation in the SMP domain for various single-crystal specimens (superconducting cuprates and iron-based superconductors), of different pinning strengths, with the external magnetic field H oriented along the crystallographic c axis or perpendicular to it. The sample independent aspects revealed by the relaxation results are the absence of single-vortex collective pinning around the SMP onset field and the sign changing of the vortex creep exponent between the onset field and the peak field. This general behavior supports strongly the pinning-induced disordering of the low-H quasi-ordered vortex solid as the actual scenario for the SMP.
75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
Tunable Optical Behaviour and Room Temperature Ferromagnetism of Cobalt-Doped BaSnO{sub 3} Nanostructures
In this work, the effect of Co doping on the structural, vibrational, morphological, optical and magnetic behaviour of BaSnO{sub 3} nanostructures is reported. Pure and Co (1,3, and 5%)-doped barium stannate (BSO) nanostructures were prepared by conventional hydrothermal technique followed by calcination at 900 °C for 5 h. The single crystalline cubic phase was identified by XRD analysis and structural distortions associated with Co doping were evidenced by variation in microstarin and crystallite size. FTIR and Raman studies further confirm the structural quality of the prepared samples. FESEM analysis revealed the mixed morphology of prepared samples, and the chemical compositions of all the samples were analysed using EDAX studies. The absorption studies revealed the incorporation of dopant ions and their effect on the bandgap subsequently in samples. The presence of defects and paramagnetic centres in the samples were confirmed by PL and EPR analyses. Magnetization studies demonstrated that pure BSO exhibits characteristic diamagnetism at room temperature and the addition of Co into Ba–Sn–O lattice drives the F-centre exchange interactions which results in the ferromagnetic behaviour. Hence, the occurrence of diamagnetic to ferromagnetic transition at room temperature with addition of Co as a dopant was identified.
75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
In-field Conductivity Fluctuations in Ba{sub 0.72}K{sub 0.28}Fe{sub 2}As{sub 2} Single Crystals
Fluctuations in the conductivity of Ba{sub 0.72}K{sub 0.28}Fe{sub 2}As{sub 2} single crystal are studied systematically by resistance measurements as a function of temperature and magnetic field. A clear Maki−Thompson and Aslamakov−Larkin (MT–AL) two- to three-dimensional (2D–3D) crossover is found on the excess conductivity (Δσ) curves as the temperature approaches the superconducting critical temperature, T{sub c}. 3D fluctuations in superconductivity are realized near T{sub c} that are well fitted to experimental data by the 3D Aslamazov–Larkin theory. The Maki–Thompson model shows a 2D conductivity fluctuation above the 2D-3D temperature transition, T{sub 0}, which depends on magnetic field. Results show that the 2D-3D dimensional crossover moves to lower temperature with increasing magnetic field. The values of the transition temperature and the crossover in the reduced temperature, ln(ε{sub 0}), as functions of magnetic field were used to determine the coherence length and the lifetime, τ{sub φ}, of the fluctuational pairs at the temperature of 35 K. Analysis of the Ba{sub 0.72}K{sub 0.28}Fe{sub 2}As{sub 2} single crystal gives a value of 3.76 × 10{sup − 12} s for the τ{sub φ} in the absence of magnetic field and it decreases to 2.4 × 10{sup − 12} s in magnetic field of 13 T.
75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
On the Origin of Enhanced Critical Current Density and Thermal-Activated Flux Flow in K{sub x}Fe{sub 2−y}Se{sub 2} Superconductors: the Effect of Quenching and Mn Doping
A magnetotransport, vortex pinning, and critical current density study of superconducting K{sub 0.8}Fe{sub 2−z}Mn{sub z}Se{sub 2} (z = 0, 0.02) single crystals is reported. The parameters of upper critical field, coherence length, and anisotropic ratio at 0 K are presented. Based on thermally activated flux flow model, the values of pinning potential, U{sub 0}{sup ∥{sub c}}(U{sub 0}{sup ∥{sub a}{sub b}}), at 0.25 T are derived to be as large as 1.3 × 10{sup 4}(1.8 × 10{sup 4}) K for z = 0.02, which shows rather robust and retains still larger than pure ones up to 9 T. Utilizing scanning electron microscope, it is revealed the increased magnitude of magnetic moment in magnetic hysteresis loops correlates well with the crystal morphology variation. The evidence on the inhomogeneous distribution of Mn dopants between the matrix and stripe phase is also shown. Furthermore, the temperature dependence of critical current density is analyzed by different pinning regimes and the model of granular superconductor. It is demonstrated that the Josephson coupling between superconducting grains exists in quenched K{sub 0.8}Fe{sub 2−y}Se{sub 2}. However, for Mn-doped sample, the Mn dopant can induce strong vortex pinning in the form of fine K–Mn–Se inclusions.
75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
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↗
Evolution of Intrinsic and Magnetic Field-Induced Magnetic Anisotropies in Strongly Phase-Separated Manganite Thin Films
Single crystalline thin film (∼ 100 nm) of La{sub 0.18}Pr{sub 0.40}Ca{sub 0.42}MnO{sub 3} is grown on (001) oriented LaAlO{sub 3} substrates and the evolution of anisotropy associated with the supercooling behaviour of the magnetic liquid is studied as a function of temperature and magnetic field. The angle-dependent magnetization measurements ascertain that the easy magnetic axis lies in the plane of the film while the hard axis is along the plane normal. The ratio of the easy and hard axes magnetizations (M{sub ||} and M{sub ⊥}) measured at 10 K, viz., M{sub ||}/M{sub ⊥} (10 K) = 2.6, confirms the strongly anisotropic nature of the film. The easy axis ferromagnetic (FM) transition temperature (T{sub C}) is smaller than that along the hard axis. The giant hysteresis in FCC–FCW M–T, which manifests the magnetic liquid behaviour of the strongly phase-separated manganites is appreciably narrowed along the hard axis. The strain glass state is also less dominant along the easy axis. The analysis of the M–H data brings out that the easy axis remanence (M{sub r||}) shows a nonlinear temperature dependence, while the one corresponding to the hard axis (M{sub r⊥}) shows a nearly linear behaviour. The coercivity (H{sub C}) follows a law of the type H{sub C}(T)=H{sub C}(0)(1−AT{sup b}). The value of exponent b ∼ 0.5 for single-domain particles, but in the present case, the best fit to the experimental data yields the exponent b ≈ 0.25 for both H{sub C||} and H{sub C⊥}. The smaller value of the exponent is attributed to the non-canonical nature of the ferromagnetic state and the associated strongly phase-separated nature of the LPCMO thin film.
75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
{sup 75}As NMR and XRD Study of Structural and Electronic Inhomogeneities in Ba(Fe{sub 1−x}Ni{sub x}){sub 2}As{sub 2}
We have used {sup 75}As NMR and x-ray diffraction analysis to study the structural and electronic inhomogeneities in Ba(Fe{sub 1−x}Ni{sub x}){sub 2}As{sub 2} crystals with x near the border of the antiferromagnetic domain. Unequal nickel population of the equivalent Fe planes and rather homogeneous distribution of Ni inside the planes have been found in the well-ordered single crystal with x = 0.036. Below 40 K a signal wipeout of {sup 75}As NMR spectra is observed for the crystals with x = 0.036 and 0.037. This fact together with spin-lattice relaxation peculiarities is treated a result of the system glassy behavior in this region of the phase diagram. The {sup 75}As NMR data also indicate on partial suppression of antiferromagnetic spin fluctuations around the Ni impurity in these crystals at low temperatures.
75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗