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At least 361 records · Page 20
All sourcesNASA NTRSDOE OSTI
NASA NTRS1977

Computer simulation of the motion of a straight dislocation line in concentrated solid solutions. II

An investigation was undertaken to determine if the size and modulus interaction of a solute atom with a screw dislocation and the modulus interaction with an edge dislocation contributed to strengthening, in addition to the size interaction with an edge dislocation. The results indicate that the size interaction between solute atom and an edge dislocation accounts for most of the solid solution strengthening in f.c.c. alloys. The contribution to the yield stress from the modulus interaction with an edge dislocation is less than 15%. The interaction between a solute atom and a screw dislocation is much less than that between a solute atom and an edge dislocation.

Kuo, C. T. K.↗
DOE OSTI2019

Materials Based on Solid Solutions of Bismuth Chalcogenides of n-Type Conductivity Prepared by Melt Crystallization in a Liquid

The microstructure, mechanical, and thermoelectric properties of samples of the n-type Bi{sub 2}Te{sub 3}–Bi{sub 2}Se{sub 3} solid-solution samples containing 6, 8, and 10 mol % Bi{sub 2}Se{sub 3}, doped with antimony iodide, cadmium chloride, and hexabromobenzene, are investigated. The samples are formed by hot pressing and the extrusion of granules prepared by melt crystallization in a liquid and ground in a mortar, cutting mill, and ball mill. Measurements are performed at room temperature and in the range of 100–600 K. The formation conditions and compositions of materials with an ultimate compressive strength of ~250 MPa and thermoelectric efficiency of (ZT){sub max} = (0.9–1.0) in the temperature range of 320–430 K are found.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2018

Radiation-induced extreme elastic and inelastic interactions in concentrated solid solutions

One of the biggest challenges in the radiation induced defect science is to understand the complex nature of ion-atom interactions under highly extreme conditions. Here, we report the irradiation induced non-equilibrium defect formation in NiCoCr single phase concentrated solid solution alloy due to (i) the extreme inelastic and (ii) the coupled inelastic and elastic ion-atom interactions. These two conditions are achieved at 5 and 30 μm penetration depths along the paths of swift heavy ions (1.542 GeV Bi). In general, the irradiation induced damage consists of interstitial-type dislocation loops and vacancy-type stacking fault tetrahedra (SFT). Near the surface (~5 μm) where electronic energy loss is dominating (~62.5 keV nm –1 ), the atomic motion primarily results in the formation of SFT. A noticeable increase of dislocation loop formation is observed at 30 μm near the maximum energy deposition from elastic interactions (~4.9 keV nm –1 ), as compared to the near surface region (~0.06 keV nm –1 ). As a result, insights on the complex electronic and atomic correlations of extreme energy deposition and dissipation on defect dynamics and structural stability may pave the way for new design principles of radiation–tolerant structural alloys.

36 MATERIALS SCIENCE↗
DOE OSTI2019

Comparison of anion and cation dynamics in a carbon-substituted closo-hydroborate salt: 1 H and 23 Na NMR studies of solid-solution Na 2 (CB 9 H 10 )(CB 11 H 12 )

The hexagonal mixed-anion solid solution Na 2 (CB 9 H 10 )(CB 11 H 12 ) shows the highest room-temperature ionic conductivity among all known Na-ion conductors. To study the dynamical properties of this compound, we have measured the 1 H and 23 Na nuclear magnetic resonance (NMR) spectra and spin-lattice relaxation rates in Na 2 (CB 9 H 10 )(CB 11 H 12 ) over the temperature range of 80-435 K. It is found that the diffusive motion of Na+ ions can be described in terms of two jump processes: the fast localized motion within the pairs of tetrahedral interstitial sites of the hexagonal close-packed lattice formed by large anions and the slower jump process via octahedral sites leading to long-range diffusion. Below 350 K, the slower Na + jump process is characterized by the activation energy of 353(11) meV. Although Na + mobility in Na 2 (CB 9 H 10 )(CB 11 H 12 ) found from our NMR experiments is higher than in other ionic conductors, it appears to be an order-of-magnitude lower than that expected on the basis of the conductivity measurements. This result suggests that the complex diffusion mechanism and/or correlations between Na + jumps should be taken into account. The measured 1H spin-lattice relaxation rates for Na 2 (CB 9 H 10 )(CB 11 H 12 ) are consistent with a coexistence of at least two anion reorientational jump processes occurring at different frequency scales. Near room temperature, both reorientational processes are found to be faster than the Na + jump process responsible for the long-range diffusion.

25 ENERGY STORAGE↗
DOE OSTI2016

The high-temperature heat capacity of the (Th,U)O 2 and (U,Pu)O 2 solid solutions

The enthalpy increment data for the (Th,U)O 2 and (U,Pu)O 2 solid solutions are reviewed and complemented with new experimental data (400–1773 K) and many-body potential model simulations. The results of the review show that from room temperature up to about 2000 K the enthalpy data are in agreement with the additivity rule (Neumann-Kopp) in the whole composition range. Above 2000 K the effect of Oxygen Frenkel Pair (OFP) formation leads to an excess enthalpy (heat capacity) that is modeled using the enthalpy and entropy of OFP formation from the end-members. Here, a good agreement with existing experimental work is observed, and a reasonable agreement with the results of the many-body potential model, which indicate the presence of the diffuse Bredig (superionic) transition that is not found in the experimental enthalpy increment data.

36 MATERIALS SCIENCE↗
DOE OSTI2022

Phase stability, mechanical properties, and ion irradiation effects in face-centered cubic CrFeMnNi compositionally complex solid-solution alloys at high temperatures

We report two CrFeMnNi face-centered cubic complex concentrated solid-solution alloys (CSA) have been evaluated for phase stability, mechanical properties, and radiation damage effects from heavy ions. Cr 18 Fe 27 Mn 27 Ni 28 and Cr 15 Fe 35 Mn 15 Ni 35 were predicted by thermodynamic calculations to phase separate and maintain a single phase at 700 °C, respectively. Aging experiments at this temperature confirmed varying degrees of precipitation of a body-centered cubic phase in both Cr 18 Fe 27 Mn 27 Ni 28 and Cr 15 Fe 35 Mn 15 Ni 35 . The alloys showed promising strength in tensile deformation at room temperature, with yield strengths of 155 MPa and 151 MPa for Cr 18 Fe 27 Mn 27 Ni 28 and Cr 15 Fe3 5 Mn 15 Ni 35 , respectively. At 500 °C, the yield strength of Cr 18 Fe 27 Mn 27 Ni 28 fell to 93 MPa, and to 100 MPa in Cr 15 Fe3 5 Mn 15 Ni 35 . Unlike Cr 18 Fe 27 Mn 27 Ni 28 , Cr 15 Fe 35 Mn 15 Ni 35 gained some ductility at 500 °C compared to room temperature. The two CSAs were irradiated to 75 dpa at 500 °C in the plateau region of the displacement curve using 3.7 MeV Ni 2+ ions, alongside model alloy 709 as a reference. Irradiation results produced similar densities and sizes of dislocations loops in the two CSAs compared to the reference. However, while large voids form in the plateau region of Cr 18 Fe 27 Mn 27 Ni 28 , small voids form just beyond the displacement peak of Cr 15 Fe 35 Mn 15 Ni 35 . Atom probe tomography and energy dispersive X-ray spectroscopy-equipped scanning transmission electron microscopes were used to characterize the alloys for changes in chemical distribution.

11 NUCLEAR FUEL CYCLE AND FUEL MATERIALS↗
DOE OSTI2016

Effects of Fe concentration on the ion-irradiation induced defect evolution and hardening in Ni-Fe solid solution alloys

Understanding alloying effects on the irradiation response of structural materials is pivotal in nuclear engineering. In order to systematically explore the effects of Fe concentration on the irradiation-induced defect evolution and hardening in face-centered cubic Ni-Fe binary solid solution alloys, single crystalline Ni-xFe (x = 0–60 at%) alloys have been grown and irradiated with 1.5 MeV Ni ions. The irradiations have been performed over a wide range of fluences from 3 × 10 13 to 3 × 10 16 cm -2 at room temperature. Ion channeling technique has shown reduced damage accumulation with increasing Fe concentration in the low fluence regime, which is consistent to the results from molecular dynamic simulations. We did not observe any irradiation-induced compositional segregation in atom probe tomography within the detection limit, even in the samples irradiated with high fluence Ni ions. Transmission electron microscopy analyses have further demonstrated that the defect size significantly decreases with increasing Fe concentration, indicating a delay in defect evolution. Furthermore, irradiation induced hardening has been measured by nanoindentation tests. Ni and the Ni-Fe alloys have largely different initial hardness, but they all follow a similar trend for the increase of hardness as a function of irradiation fluence.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Effects of Fe concentration on helium bubble formation in NiFe x single-phase concentrated solid solution alloys

The formation of helium bubbles and the consequential property degradation are critical challenges for materials used in advanced nuclear energy systems. The mechanism of helium bubble formation in a series of NiFe x (x = 0, 20, 35, or 50 at.%) single-phase concentrated solid solution alloys (SP-CSAs) are studied in this work. Transmission electron microscopy analysis shows that with increasing Fe concentration, the average bubble size decreases while the bubble number density increases, indicating the growth of large helium bubbles in NiFe x SP-CSAs is suppressed by increasing the alloy chemical complexity through increased Fe concentration. Mechanisms for the slower bubble growth rate in NiFe x binary SP-CSAs compared Ni are identified. These mechanisms include promotion of Frenkel pair recombination, denser and more homogeneously distributed nucleation sites, and increased helium atom densities inside the bubbles. Here, the results demonstrate that optimizing the chemical complexity in SP-CSAs can be an effective approach to design materials with superior resistance to helium bubble nucleation and growth.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Predicting the Phase Stability of Sc{sub 1–x}Ln{sub x}PO{sub 4} (Ln = Gd–Lu, Y) Zircon-Structured Solid Solutions

The energies of mixing (interaction parameters) in the Sc{sub 1–x}Ln{sub x}PO{sub 4} (Ln = Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, Y) systems have been calculated using Urusov’s crystal energy theory of isomorphous substitutions. The decomposition (stability) temperatures of the solid solutions have been plotted against the atomic number of the rare-earth elements at x = 0.01, 0.03, 0.05, 0.10, 0.20, and 0.50. The present results can be helpful in a search for host and activator compositions for new luminescence, laser, and other materials based on the zircon-structured rare-earth orthophosphates.

36 MATERIALS SCIENCE↗
DOE OSTI2019

On the Relationship Between Dislocation Creep Strength and Microstructure of a Solid-Solution-Strengthened Ni-Base Superalloy

It is shown that the dislocation creep strength of a solid-solution-strengthened Ni-base superalloy is critically dependent upon the cooling rate from the annealing temperature. This behavior is correlated with the effect of cooling rate on the morphology of M{sub 23}C{sub 6}-type carbide which precipitates at grain boundaries during cooling. Experiment shows that the creep strength is enhanced by rapid cooling which results in discrete carbide particles with irregular shape following a zigzag path along the grain boundaries. However, the creep strength is degraded as the morphology is changed into lamellar type by a discontinuous grain boundary reaction which occurs during slower cooling rates. Due to the transition from the discrete particle into the lamellar morphology, plastic deformation becomes more localized alongside the grain boundaries which accelerates the creep rate leading to premature intergranular failure. On the other hand, it is also shown that the stacking fault energy of the alloy increases with temperature which can allow dislocations to rearrange themselves into subgrain structure with relative ease during steady-state creep.

36 MATERIALS SCIENCE↗
DOE OSTI2019

Effect of the Copper Content on the Kinetics of the Microwave Photoconductivity of CIGS Solid Solutions

The kinetics of the photoresponse of microwave photoconductivity (9 GHz, TE{sub 101}-type cavity) on excitation by laser light pulses with a wavelength of 337 nm and a duration of 8 ns in copper-deficient Cu{sub 1 –x}(In{sub 0.7}Ga{sub 0.3})Se{sub 2} (CIGS) (0 < x ≤ 0.4) solid solutions with the chalcopyrite structure is investigated in a wide light intensity range. With an increase in the laser radiation density to ~5 × 10{sup 14} photon/cm{sup 2} per pulse, the photoresponse acquires, along with the previously revealed skin effect, the effect of the filling of traps created by V{sub Cu} vacancies and Cu{sup +2} · V{sub Cu} defect associates, the concentration of which increases with a decrease in x in the CIGS formula.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2013

Unification of the negative electrocaloric effect in Bi{sub 1/2}Na{sub 1/2}TiO{sub 3}-BaTiO{sub 3} solid solutions by Ba{sub 1/2}Sr{sub 1/2}TiO{sub 3} doping

The microscopic mechanisms of the negative electrocaloric effect (ECE) of the single-phase (1−x)(0.94Bi{sub 1/2}Na{sub 1/2}TiO{sub 3}-0.06BaTiO{sub 3})-xBa{sub 1/2}Sr{sub 1/2}TiO{sub 3} (BNT-BT-BST) perovskite solid solutions fabricated via the sol-gel technique are explored in this study. Dielectric and mechanical relaxation analyses are employed to investigate the ferroelectric and structural transitions of the samples. The electrocaloric properties of the samples were measured by thermodynamics Maxwell relations. The difference between the depolarization temperature (T{sub d}) and the maximum dielectric constant temperature (T{sub m}) was found to decrease with increasing BST content. Doping with BST stabilized the ferroelectric phase along with unifying the EC temperature changes (ΔT) to only negative values. The origin of the uniform negative ECE of BNT-BT-BST is discussed.

36 MATERIALS SCIENCE↗
DOE OSTI2014

Chemical pressure effects on structural, dielectric and magnetic properties of solid solutions Mn{sub 3−x}Co{sub x}TeO{sub 6}

Highlights: • Mn{sub 3}TeO{sub 6} and Co{sub 3}TeO{sub 6} are antiferromagnets with corundum related structures. • The structural and magnetic properties of Mn{sub 3−x}Co{sub x}TeO{sub 6} ceramics were investigated. • All compounds adopt the trigonal structure of Mn{sub 3}TeO{sub 6} up to at least x = 2.4. • The antiferromagnetic transition temperature monotonously increases with x. • NPD data evidences the magnetic structure of the Mn{sub 3−x}Co{sub x}TeO{sub 6} ceramics. - Abstract: The effects of Co{sup 2+} doping on the structural, magnetic and dielectric properties of the multiferroic frustrated antiferromagnet Mn{sub 3}TeO{sub 6} have been investigated. Ceramic samples of the solid solution series Mn{sub 3−x}Co{sub x}TeO{sub 6} were prepared by a solid-state reaction route. X-ray and neutron powder diffraction and electron microscopy techniques were combined with calorimetric, dielectric and magnetic measurements to investigate the dependence of the crystal structure and physical properties on temperature and composition. It is shown that the compounds with x ≤ 2.4 adopt the trigonal corundum-related structure of pure Mn{sub 3}TeO{sub 6} (space group R3{sup ¯}) in the temperature range 5–295 K and that the lattice parameters a and c and the unit-cell volume V decrease linearly with increasing Co{sup 2+} concentration. The low-temperature magnetic susceptibility and heat capacity data evidence the antiferromagnetic ordering of all samples. The Neel temperature linearly increases with Co{sup 2+} concentration x. Curie–Weiss fits of the high temperature susceptibility indicate that the magnetic frustration decreases with x. The derived magnetic structure of Mn{sub 3}TeO{sub 6} can be described as an incommensurately modulated magnetic spin state with k = [0, 0, k{sub z}] and an elliptical spin-spiral order of spins within the chains of MnO{sub 6} octahedra. With increasing Co{sup 2+} concentration the propagation vector k{sub z} changes from 0.453 (x = 0) to 0.516 (x = 2.4). The magnetic anisotropy changes as well, leading to a reorientation of the spiral-basal plane. A possible coexistence of long-range order of electrical dipoles and magnetic moments in Mn{sub 3−x}Co{sub x}TeO{sub 6} is discussed.

36 MATERIALS SCIENCE↗
DOE OSTI2016

X-ray diffraction studies of the Tl(GaS{sub 2}){sub 1–x}(InSe{sub 2}){sub x} solid solutions

The unit-cell parameters of crystals obtained in the Tl(GaS{sub 2}){sub 1–x}(InSe{sub 2}){sub x} system are measured by X-ray diffraction. The relationship between these parameters and composition is determined. It is shown that, with growing x, the a, b, and c parameters increase and the β angle decreases. Two types of solid solutions are found in the Tl(GaS{sub 2}){sub 1–x}(InSe{sub 2}){sub x} system: one is based on compound TlGaS{sub 2} with monoclinic structure and the other is based on TlInSe{sub 2} with tetragonal structure.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2017

Photoluminescence of perovskite CsPbX{sub 3} (X = Cl, Br, I) nanocrystals and solid solutions on their basis

Synthesis and also the structural and photoluminescence properties of nanocrystals with natural faceting of the “cesium–lead–halogen” system with crystalline structure of the perovskite type are examined. The possibility of continuously changing the position of the maximum in the photoluminescence spectrum in the wavelength range of 400–700 nm is demonstrated. Features of the formation of the continuous series of solid solutions CsPb(Cl{sub 1–x}Br{sub x}){sub 3} and CsPb(Br{sub 1–x}I{sub x}){sub 3} due to the aftergrowth treatment of CsPbBr{sub 3} nanocrystals as a result of anion exchange at room temperature are studied. The corresponding range of frequency change for the maximum of the photoluminescence spectrum amounts to 410–690 nm.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Tellurium Solubility in TlGaTe{sub 2} and TlInTe{sub 2} and the Electrophysical Properties of Solid Solutions

The complex methods of the physicochemical analysis are used to study TlGaTe{sub 2}–Te and TlInTe{sub 2}–Te alloys in which the tellurium solubility region up to 5.0 at % is observed. The temperature dependences of the lattice parameters and the electrical conductivity of TlGaTe{sub 2+x} and TlInTe{sub 2+x} have been studied in different crystallographic directions. The TlGaTe{sub 2+x} and TlInTe{sub 2+x} solid solutions undergo a phase transition at a temperature of 498 K. The transition nature is interpreted.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2023

Melting and crystallization peculiarities in Cd0.50Mn0.50Te solid solutions

We investigated melting and crystallization processes of Cd0.50Mn0.50Te. Using differential thermal analysis (DTA) we studied the solid-liquid equilibrium temperature range, the temperature dependence of the volume fraction of the solid phase in the melt, and crystallization peculiarities. We observed that changing a dwell temperature from 1346 to 1354 K results in an increase of the crystallization temperature of the Cd0.50Mn0.50Te melt. Since the melt is in a semi-liquid state, its crystallization occurs over a solid-phase domain. It was found that a slightly overheated Cd0.50Mn0.50Te melt (up to 10 K) crystallizes more slowly than more overheated melts, and that the Cd0.50Mn0.50Te solid solutions are in a semi-liquid state in the temperature range of 1338 – 1354 K.

Kopach, Oleh↗
DOE OSTI2013

Microstructure characterization and electrical transport of nanocrystalline ZrO{sub 2}–CeO{sub 2} solid solution

Graphical abstract: - Highlights: • Monoclinic ZrO{sub 2} phase has been changed to cubic ZrO{sub 2} phase within a short milling. • Conductivity increases due to change of phase from monoclinic to cubic. • A maximum has been observed in the s–T curve. • A transformation from −ve to +ve ac magnetoconductance has been observed. - Abstract: Nanocrystalline ZrO{sub 2}–CeO{sub 2} (ZC) solid solution is synthesized by high energy ball-milling the powder mixture of monoclinic (m) ZrO{sub 2}–10 mol% CeO{sub 2} in air medium. X-ray powder diffraction (XRD) patterns show that the method IS effective to synthesize cubic (c) ZrO{sub 2} phase within a short milling time. Formation mechanism, structural and microstructural changes of different phases and relative phase abundances have been estimated by Rietveld analysis of XRD patterns. The dc conductivity has been enhanced due to monoclinic to cubic phase transformation. A transformation from small polaron hopping to correlated barrier hoping has been observed from the of temperature dependence frequency exponent study. A crossover from negative to positive ac magnetoconductance has been observed at temperature T = 280 K and 230 K for unmilled (ZC0H) and 8 h (ZC8H) milled samples, respectively.

36 MATERIALS SCIENCE↗