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At least 163 records · Page 9
All sourcesNASA NTRSDOE OSTI
DOE OSTI2020

Synthesis and flash sintering of (Hf 1-x Zr x )B 2 solid solution powders

(Hf 1-x Zr x )B 2 solid solution powders were synthesized by two methods. First, solution-based processing of HfCl 4 , ZrCl 4 , sucrose, and H 3 BO 3 was conducted followed by heat treatment in Argon to carry out the carbothermal reduction (CTR) reaction to form the diboride powders. Alternatively, in the so-called borohydride reduction (BHR) method, HfCl 4 , ZrCl 4 and NaBH 4 were mixed in an Argon glove box followed by heat treatment in Argon at 700-1500°C. The synthesized powders were characterized by XRD, SEM, TEM, EDS, and TGA, and the influence of different parameters such as starting composition, heat treatment temperature and time on products characteristics were revealed. Both CTR and BHR solid solution powders were then consolidated within ~5 min in a homemade flash sintering (FS) setup. Here, the composition, microstructure, hardness, and thermal-oxidation properties of flash sintered ceramics were characterized, and the implication of this study and directions for future research were discussed.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Exciton diffusion in solid solutions of luminescent lanthanide β-diketonates

In this article, a series of luminescent lanthanide β-diketonate solid solutions, with the formula of TBAEu x M 1– x (TTA) 4 (TBA = tetrabutylammonium; M = La or Gd; TTA = 2-thenoyltrifluoroacetonate), are synthesized by co-precipitation. In the solid solutions, the emission efficiency of Eu 3+ is significantly increased with the presence of non-luminescent chelates TBALa(TTA) 4 and TBAGd(TTA) 4 . Low temperature luminescence spectroscopy studies indicate that the TTA – ligands in these non-luminescent chelates do emit phosphorescence with long lifetime. However, the ligand phosphorescence is strongly quenched in solid solutions with the luminescent chelate TBAEu(TTA) 4 , providing strong evidence for intermolecular energy transfer through the triplet excited states of the ligands. Here, a quantitative analysis of Eu 3+ emission enhancement and TTA – phosphorescence quenching reveals that each Eu 3+ center may receive excitation energy from about 30 TTA – ligands, suggesting that the excitation energy has become exciton-like in the solid solutions. Based on the crystallography analysis of TBALn(TTA) 4 , it is discovered that TTA – ligands in neighboring Ln(TTA) 4 – units may form π–π stacks with intermolecular distance ≤3.5 Å, thus enabling efficient triplet exciton diffusion via exchange interaction.

36 MATERIALS SCIENCE↗
DOE OSTI2012

Intermetallic solid solution Fe{sub 1-x}Co{sub x}Ga{sub 3}: Synthesis, structure, NQR study and electronic band structure calculations

Unlimited solid solution Fe{sub 1-x}Co{sub x}Ga{sub 3} was prepared from Ga flux. Its crystal structure was refined for Fe{sub 0.5}Co{sub 0.5}Ga{sub 3} (P4{sub 2}/mnm, a=6.2436(9), c=6.4654(13), Z=4) and showed no ordering of the metal atoms. A combination of the electronic band structure calculations within the density functional theory (DFT) approach and {sup 69,71}Ga nuclear quadrupole resonance (NQR) spectroscopy clearly shows that the Fe-Fe and Co-Co dumbbells are preferred to the Fe-Co dumbbells in the crystals structure. The band structure features a band gap of about 0.4 eV, with the Fermi level crossing peaks of a substantial density of electronic states above the gap for x>0. The solid solution is metallic for x>0.025. The study of the nuclear spin-lattice relaxation shows that the rate of the relaxation, 1/T{sub 1}, is very sensitive to the Co concentration and correlates well with the square of the density of states at the Fermi level, N{sup 2}(E{sub F}). - Graphical abstract: Rate of the nuclear spin-lattice relaxation, 1/T{sub 1}, observed in the {sup 69}Ga NQR experiments for the intermetallic solid solution Fe{sub 1-x}Co{sub x}Ga{sub 3} is the highest for x=0.25 with the highest calculated density of electronic states at the Fermi level, N(E{sub F}); in general, 1/T{sub 1} correlates with N{sup 2}(E{sub F}). Highlights: Black-Right-Pointing-Pointer Fe{sub 1-x}Co{sub x}Ga{sub 3} solid solution is prepared in single crystalline form from Ga flux. Black-Right-Pointing-Pointer In the crystal structure Fe-Fe and Co-Co dumbbells are preferred to Fe-Co dumbbells. Black-Right-Pointing-Pointer Metal-to-semiconductor transition occurs at 0<x<0.025. Black-Right-Pointing-Pointer {sup 69,71}Ga NQR spectra efficiently probe local environment of two independent Ga atoms. Black-Right-Pointing-Pointer Rate of nuclear spin-lattice relaxation follows squared DOS at the Fermi level.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2022

Energetics of hydroxylbastnäsite solid solutions, La 1-$\chi$ Nd $\chi$ CO 3 OH

Bastnäsites (LnCO 3 (F,OH)) are a group of common rare earth elements (REE)-bearing minerals and are one of the primary global sources of REE. Due to the chemical similarities among REE, bastnӓsites tend to occur as solid solutions instead of end members in REE containing ores. To better understand the processes and the mechanisms of formation of such deposits, it is essential to determine the thermodynamic properties of bastnӓsites, including hydroxylbastnӓsite (LnCO 3 OH) solid solutions. In this work, we performed detailed structural and calorimetric investigations on synthetic hexagonal La–Nd hydroxylbastnӓsite (La 1-$\chi$ NdCO 3 OH, $\chi$ = 0, 0.25, 0.5, 0.75, 1) solid solutions. X-ray diffraction confirms the crystal structure of the solid solution series in the $\ P$6 space group, and pair distribution function (PDF) analysis reveals local bonding environments characterized by three different types of 9-coordinated metal-oxygen polyhedra. Unit cell parameters of La1–xNdxCO3OH exhibit a nearly linear relation with the Nd content x, suggesting a random distribution of La and Nd in the structure. Their standard enthalpies of formation (Δ$\ H$° f ) were determined by high temperature oxide melt drop solution calorimetry, from which the enthalpies of mixing (Δ$\ H$ mix ) were derived. The Δ$\ H$ mix can be fitted by a regular solution model with an interaction parameter of 12.58 ± 0.16 kJ/mol, suggesting enthalpic metastability of La1–xNdxCO3OH relative to the two endmembers. Combining entropy and enthalpy, we further estimated the Gibbs free energies of mixing (Δ$\ G$ mix ) at relevant temperatures, revealing favorable temperatures under which the intermediate La 1-$\chi$ NdCO 3 OH phases can be stabilized. Such entropy-driven stabilization, as is consistent with our geochemical modeling results, may explain the enhancement of thermal stability of the solid solutions in nature. Additionally, the temperature range constrained from this study may be used to estimate the thermal history of REE bastnӓsite deposit.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2018

Distribution of P{sub 2}O{sub 5} and Na{sub 2}O Between Solid Solution and Liquid Phase in the CaO-SiO{sub 2}-Fe{sub 2}O{sub 3}-P{sub 2}O{sub 5}-Na{sub 2}O Slag System with High P{sub 2}O{sub 5} Content

The phosphorus content in hot metal will increase in future, because iron ores are steadily deteriorating in quality. Na{sub 2}O addition to slag is considered an effective method for increasing the efficiency of dephosphorization. In addition, Na{sub 2}O modification also facilitates phosphorus recovery from dephosphorization slag with high P{sub 2}O{sub 5} content by selective leaching. Therefore, it is necessary to investigate the distribution ratios of P{sub 2}O{sub 5} and Na{sub 2}O between solid solution and liquid phase in the CaO-SiO{sub 2}-Fe{sub 2}O{sub 3}-P{sub 2}O{sub 5}-Na{sub 2}O slag system. A linear relationship was found between the distribution ratio of P{sub 2}O{sub 5} and the Na{sub 2}O content in slag, and was independent of P{sub 2}O{sub 5} content. When the Na{sub 2}O content was high, the Na{sub 2}O content in the solid solution approached saturation and a new 2CaO·SiO{sub 2}-2CaO·Na{sub 2}O·P{sub 2}O{sub 5} solid solution formed. The addition of Na{sub 2}O decreased the P{sub 2}O{sub 5} content in solid solution, while it increased the mass fraction of solid solution in slag. The distribution ratio of P{sub 2}O{sub 5} increased with increase in the Fe{sub 2}O{sub 3} content and basicity of slag. An increase in P{sub 2}O{sub 5} content in slag results in an increase in the activity coefficient of P{sub 2}O{sub 5} both in the liquid phase and in the solid solution.

36 MATERIALS SCIENCE↗
DOE OSTI2014

Ab initio calculation of excess properties of La{sub 1−x}(Ln,An){sub x}PO{sub 4} solid solutions

We used ab initio computational approach to predict the excess enthalpy of mixing and the corresponding regular/subregular model parameters for La{sub 1−x}Ln{sub x}PO{sub 4} (Ln=Ce,…, Tb) and La{sub 1−x}An{sub x}PO{sub 4} (An=Pu, Am and Cm) monazite-type solid solutions. We found that the regular model interaction parameter W computed for La{sub 1−x}Ln{sub x}PO{sub 4} solid solutions matches the few existing experimental data. Within the lanthanide series W increases quadratically with the volume mismatch between LaPO{sub 4} and LnPO{sub 4} endmembers (ΔV=V{sub LaPO{sub 4}}−V{sub LnPO{sub 4}}), so that W(kJ/mol)=0.618(ΔV(cm{sup 3}/mol)){sup 2}. We demonstrate that this relationship also fits the interaction parameters computed for La{sub 1−x}An{sub x}PO{sub 4} solid solutions. This shows that lanthanides can be used as surrogates for investigation of the thermodynamic mixing properties of actinide-bearing solid solutions. - Highlights: • The excess enthalpies of mixing for monazite-type solid solutions are computed. • The excess enthalpies increase with the endmembers volume mismatch. • The relationship derived for lanthanides is transferable to La{sub 1−x}An{sub x}PO{sub 4} systems.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2016

Mechanisms of radiation-induced segregation in CrFeCoNi-based single-phase concentrated solid solution alloys

Single-phase concentrated solid solution alloys have attracted wide interest due to their superior mechanical properties and enhanced radiation tolerance, which make them promising candidates for the structural applications in next-generation nuclear reactors. However, little has been understood about the intrinsic stability of their as-synthesized, high-entropy configurations against radiation damage. In this paper, we report the element segregation in CrFeCoNi, CrFeCoNiMn, and CrFeCoNiPd equiatomic alloys when subjected to 1250 kV electron irradiations at 400 °C up to a damage level of 1 displacement per atom. Cr/Fe/Mn/Pd can deplete and Co/Ni can accumulate at radiation-induced dislocation loops, while the actively segregating elements are alloy-specific. Moreover, electron-irradiated matrix of CrFeCoNiMn and CrFeCoNiPd shows L1 0 (NiMn)-type ordering decomposition and <001>-oriented spinodal decomposition between Co/Ni and Pd, respectively. Finally, these findings are rationalized based on the atomic size difference and enthalpy of mixing between the alloying elements, and identify a new important requirement to the design of radiation-tolerant alloys through modification of the composition.

36 MATERIALS SCIENCE↗
DOE OSTI2015

Liquid-phase epitaxy of the (Si{sub 2}){sub 1−x−y}(Ge{sub 2}){sub x}(GaAs){sub y} substitutional solid solution (0 ≤ x ≤ 0.91, 0 ≤ y ≤ 0.94) and their electrophysical properties

(Si{sub 2}){sub 1−x−y}(Ge{sub 2}){sub x}(GaAs){sub y} substitutional solid solutions (0 ≤ x ≤ 0.91, 0 ≤ y ≤ 0.94) are grown by liquid-phase epitaxy from a Pb-based solution-melt on Si substrates with the (111) crystallographic orientation. The chemical composition of the epitaxial films is studied by X-rays probe microanalysis, and the distribution profile of solid solution components is determined. Spectral dependences of the photosensitivity and photoluminescence of the n-Si-p(Si{sub 2}){sub 1−x−y}(Ge{sub 2}){sub x}(GaAs){sub y} heterostructures are studied at room and liquid-nitrogen temperatures. Two maxima are found in the photoluminescence spectra of the (Si{sub 2}){sub 1−x−y}(Ge{sub 2}){sub x}(GaAs){sub y} films (0 ≤ x ≤ 0.91, 0 ≤ y ≤ 0.94) against the background of a broad emission spectrum. The fundamental maximum with an energy of 1.45 eV is caused by the band-to-band recombination of solid solution carriers, and an additional maximum with an energy of 1.33 eV is caused by the recombination of carriers with the participation of impurity levels of the Si-Si bond (Si{sub 2} is covalently coupled with the tetrahedral lattice of the solid solution host)

36 MATERIALS SCIENCE↗
DOE OSTI2012

Existence of a solid solution from brucite to {beta}-Co(OH){sub 2}

Highlights: Black-Right-Pointing-Pointer A solid solution exist between Mg(OH){sub 2} and {beta}-Co(OH){sub 2}. Black-Right-Pointing-Pointer Synthesis has been performed through an easy and fast coprecipitation route. Black-Right-Pointing-Pointer No long range-ordering of the cations occurs. -- Abstract: This study shows that between brucite (Mg(OH){sub 2}) and {beta}-Co(OH){sub 2}, all the compositions are possible. The solid solution Mg{sub 1-x}Co{sub x}(OH){sub 2} has been synthesized by an easy and fast coprecipitation route and characterized by XRD and TEM. Single phase powders have been obtained. The particles exhibit platelets morphology with a size close to one hundred nanometers. XRD analysis shows an evolution of the cell parameters when x increases and demonstrates that no ordering of the cations occurs. However, extra reflections on TEM electron diffraction patterns seem to indicate that local ordering can exist. The compounds issued from this solid solution could be good candidates as precursors in order to obtain Mg-Co mixed oxide with all possible cationic ratios.

36 MATERIALS SCIENCE↗
DOE OSTI2014

Synthesis and characterisation of In-doped MnWO{sub 4}-type solid-solutions: Mn{sub 1−3x}In{sub 2x}□{sub x}WO{sub 4} (x=0–0.11)

Substitution of In{sup 3+} for Mn{sup 2+} in MnWO{sub 4}, which is one of the most studied multiferroics, was conducted systematically by solid-state reactions at 1050 °C to obtain a series of Mn{sub (1−3x)}In{sub 2x}□{sub x}WO{sub 4} solid solutions (x=0–0.11; the box indicates vacancy). The successful In-doping could be proven by electron microprobe, and statically disordered structures of this solid solution series were elucidated by Rietveld analyses with X-Ray powder diffraction (XPD) data. Its average structure maintains the space group P2/c at least up to the replacement of 33 at% Mn. The tendency of their unit cells proportionally enlarging with In-doping is an unexpected observation because In{sup 3+} is smaller than Mn{sup 2+}. This could not be explained alone by average atomic bonding distances and angles evaluated from XPD data analyses. Complimentarily, micro-Raman spectra of Mn{sub (1−3x)}In{sub 2x}□{sub x}WO{sub 4} materials feature a hardening of Raman modes due to stronger atomic bonds in W{sub 2}O{sub 4} and WO{sub 2} units with increasing In-doping. This is considered as an inevitable consequence of broken bonding in directly neighbouring Mn–O bonds as the presence of In{sup 3+} in MnWO{sub 4} accompanies the creation of defects at Mn sites. The current study using XRD and micro-Raman suggests the enlarging local space around the bridging oxygen as the reason for the unexpected cell expansion when smaller In{sup 3+} along with defects replace Mn{sup 2+} in MnWO{sub 4}. - Graphical abstract: Despite of substitution of smaller In{sup 3+} for larger Mn{sup 2+}, the In-rich solid solution Mn{sub 0.71(2)}In{sub 0.19(1)}□{sub 0.10}WO{sub 4} undergoes a volume expansion of 0.4% with respect to MnWO{sub 4}. This could be explained by a local space expansion of 0.13% around bridging oxygen at O2 sites, as illustrated by dashed lines for clarity. - Highlights: • Investigation of Mn{sub (1−3x)}In{sub 2x}□{sub x}WO{sub 4} solid solutions (x=0–0.11). • An unexpected lattice expansion by In-doping. • Strong change in local environment around bridging oxygens. • Enhancement of atomic bonds in W{sub 2}O{sub 4} and WO{sub 2} units with increasing In-doping.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2016

Zn{sub 1−x}Co{sub x}WO{sub 4} (0 ≤ x ≤ 1) full range solid solution: Structure, optical properties, and magnetism

Graphical abstract: The continuous modulation on crystal structure and band gap is achieved in the Zn{sub 1−x}Co{sub x}WO{sub 4} (0 ≤ x ≤ 1) full range solid solution. - Highlights: • Zn{sub 1−x}Co{sub x}WO{sub 4} (0 ≤ x ≤ 1) solid solution was synthesized by a hydrothermal method. • They all present a single-phase in the wolframite structure with space group P2/c. • The continuous tenability in band gap was achieved in Zn{sub 1−x}Co{sub x}WO{sub 4} (0 ≤ x ≤ 1). • CoWO{sub 4} and Zn{sub 0.5}Co{sub 0.5}WO{sub 4} are antiferromagnetic and paramagnetic, respectively. - Abstract: A novel full-range solid-solution Zn{sub 1−x}Co{sub x}WO{sub 4} (0 ≤ x ≤ 1) was successfully developed via a facile one-pot hydrothermal route. The phase structure and microstructure were characterized by X-ray diffraction (XRD), Fourier-transform infrared (FTIR) spectra and scanning electron microscopy (SEM). The Zn{sub 1−x}Co{sub x}WO{sub 4} solid solution possesses similar wolframite crystal structure with the same space group P2/c. Diffuse reflection spectroscopy (DRS) measurements on Zn{sub 1−x}Co{sub x}WO{sub 4} (0 ≤ x ≤ 1) demonstrated that the optical band gap can be continuously tuned from 3.56 eV to 2.61 eV for direct transition and 1.87 eV for indirect transition, respectively, with increasing x from 0 to 1. Magnetic susceptibility measurements reveal that CoWO{sub 4} has an antiferromagnetic transition at T{sub N} = 42 K, whereas Zn{sub 0.5}Co{sub 0.5}WO{sub 4} exhibits paramagnetic behavior. Moreover, CoWO{sub 4} and Zn{sub 0.5}Co{sub 0.5}WO{sub 4} obey the Curie–Weiss law from 200 k down to 50 K, and their effective magnetic moments were determined.

36 MATERIALS SCIENCE↗
DOE OSTI2013

High-pressure phase transitions of Fe 3-x Ti x O 4 solid solution up to 60 GPa correlated with electronic spin transition

The structural phase transition of the titanomagnetite (Fe 3–x Ti x O 4 ) solid solution under pressures up to 60 GPa has been clarified by single-crystal and powder diffraction studies using synchrotron radiation and a diamond-anvil cell. Present Rietveld structure refinements of the solid solution prove that the prefered cation distribution is based on the crystal field preference rather than the magnetic spin ordering in the solid solution. The Ti-rich phases in 0.734 ≤ x ≤1.0 undergo a phase transformation from the cubic spinel of Fd3m to the tetragonal spinel structure of I4 1 /amd with c/a < 1.0. The transition is driven by a Jahn-Teller effect of IV Fe 2+ (3d 6 ) on the tetrahedral site. The c/a < 1 ratio is induced by lifting of the degeneracy of the e orbitals by raising the d x2-y2 orbital below the energy of the d z2 orbital. The distortion characterized by c/a < 1 is more pronounced with increasing Ti content in the Fe 3–x Ti x O 4 solid solutions and with increasing pressure. An X-ray emission experiment of Fe 2 TiO 4 at high pressures confirms the spin transition of FeKβ from high spin to intermediate spin (IS) state. The high spin (HS)-to-low spin (LS) transition starts at 14 GPa and the IS state gradually increases with compression. The VI Fe 2+ in the octahedral site is more prone for the HS-to-LS transition, compared with Fe 2+ in the fourfold- or eightfold-coordinated site. The transition to the orthorhombic post-spinel structure with space group Cmcm has been confirmed in the whole compositional range of Fe 3–x Ti x O 4 . The transition pressure decreases from 25 GPa (x = 0.0) to 15 GPa (x = 1.0) with increasing Ti content. There are two cation sites in the orthorhombic phase: M1 and M2 sites of eightfold and sixfold coordination, respectively. Fe 2+ and Ti 4+ are disordered on the M2 site. This structural change is accelerated at higher pressures due to the spin transition of Fe 2+ in the octahedral site. This is because the ionic radius of VI Fe 2+ becomes 20% shortened by the spin transition. At 53 GPa, the structure transforms to another high-pressure polymorph with Pmma symmetry with the ordered structure of Ti and Fe atoms in the octahedral site. This structure change results from the order-disorder transition.

Yamanaka, Takamitsu↗
DOE OSTI2017

Unique Challenges for Modeling Defect Dynamics in Concentrated Solid-Solution Alloys

Recently developed concentrated solid solution alloys (CSAs) are shown to have improved irradiation performance that strongly depends on the number of alloying elements, alloying species and their concentrations. In contrast to conventional dilute alloys, CSAs are comprised of multiple principal elements randomly situated in a simple crystalline lattice. As a result, the intrinsic disorder has a profound influence on the energy dissipation pathways and defect evolution when these CSAs are subjected to ion irradiation. Extraordinary irradiation resistance, including suppression of void formation by two orders magnitude at an elevated temperature, has been achieved with increasing compositional complexity in CSAs. Yet, the intrinsic disorder poses great challenges to theoretical modelling at the electronic and atomic level. Based on recent computer simulation results from a novel set of Ni-based face-centered cubic CSAs, we demonstrate in this review that how the disorder can be tackled in theoretical modeling and what is the impact of disorder on the defect dynamics. Finally, the unique challenges of describing the energy dissipation and defect evolution in CSAs are discussed.

36 MATERIALS SCIENCE↗
DOE OSTI2016

The exchange interactions and the state of manganese atoms in the solid solutions in Bi{sub 3}NbO{sub 7} of cubic and tetragonal modifications

The comparative analysis of magnetic behavior of manganese-containing solid solutions Bi{sub 3}Nb{sub 1−x}Mn{sub x}O{sub 7−δ} (x=0.01−0.10) of cubic and tetragonal modifications was performed. Based on the results of magnetic susceptibility studies paramagnetic manganese atoms in solid solutions of cubic and tetragonal modifications were found to be in the form of Mn(III), Mn(IV) monomers and exchange-coupled dimers of Mn(III)–O–Mn(III), Mn(IV)–O–Mn(IV), Mn(III)–O–Mn(IV). The exchange parameters and the distribution of monomers and dimers in solid solutions as a function of the content of paramagnetic atoms were calculated. - Graphical abstract: Structural transition of cubic to tetragonal Bi{sub 3}NbO{sub 7−δ}.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2012

Synthesis and characterization of Sr{sub 2}Ir{sub 1-x}M{sub x}O{sub 4} (M=Ti, Fe, Co) solid solutions

The effects of Ti, Fe and Co substitutions for Ir on the structure and on the physical properties of Sr{sub 2}IrO{sub 4} are investigated. A complete solid solution Sr{sub 2}Ir{sub 1-x}Ti{sub x}O{sub 4} is obtained while both Fe and Co doping are relatively limited. In each case however, the c-axis cell parameter and the initial IrO{sub 6} octahedra tilting decreases with substitution. Doping with Ti, Fe and Co results in a decrease of the magnetic susceptibility and in an increase in the paramagnetic effective moment for Co and Fe doped samples and a suppression of the weak ferromagnetic ordering observed for Sr{sub 2}IrO{sub 4}. - Graphical abstract: Solid solutions of Sr{sub 2}Ir{sub 1-x}M{sub x}O{sub 4} (M=Ti, Fe, Co) have been synthesized and characterized by powder X-ray diffraction, magnetism and electrical measurements. Changes in the a parameter and decreases in both the c-axis cell parameters and the initial IrO{sub 6} octahedra tilting are found to be correlated. Highlights: Black-Right-Pointing-Pointer Solid Solutions of Sr{sub 2}Ir{sub 1-x}M{sub x}O{sub 4} (M=Ti, Fe, Co) are synthesized. Black-Right-Pointing-Pointer The Sr{sub 2}Ir{sub 1-x}Ti{sub x}O{sub 4} solid solution is complete while those of Fe and Co are relatively limited. Black-Right-Pointing-Pointer The change in a cell parameter with substitution is much less than that of the c parameter. Black-Right-Pointing-Pointer Decreased tilting and the smaller size of the M cation contrastingly affect the a parameter. Black-Right-Pointing-Pointer Doping results in a suppression of the weak ferromagnetic ordering in Sr{sub 2}IrO{sub 4}.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2015

Quantitative experimental determination of the solid solution hardening potential of rhenium, tungsten and molybdenum in single-crystal nickel-based superalloys

Here, the solid-solution hardening potential of the refractory elements rhenium, tungsten and molybdenum in the matrix of single-crystal nickel-based superalloys was experimentally quantified. Single-phase alloys with the composition of the nickel solid-solution matrix of superalloys were cast as single crystals, and tested in creep at 980 °C and 30–75 MPa. The use of single-phase single-crystalline material ensures very clean data because no grain boundary or particle strengthening effects interfere with the solid-solution hardening. This makes it possible to quantify the amount of rhenium, tungsten and molybdenum necessary to reduce the creep rate by a factor of 10. Rhenium is more than two times more effective for matrix strengthening than either tungsten or molybdenum. The existence of rhenium clusters as a possible reason for the strong strengthening effect is excluded as a result of atom probe tomography measurements. If the partitioning coefficient of rhenium, tungsten and molybdenum between the γ matrix and the γ' precipitates is taken into account, the effectiveness of the alloying elements in two-phase superalloys can be calculated and the rhenium effect can be explained.

36 MATERIALS SCIENCE↗
DOE OSTI2014

Local polar structure and multiferroic properties of (1−x)Bi{sub 0.9}Dy{sub 0.1}FeO{sub 3}−xPbTiO{sub 3} solid solution

The multiferroic (1–x)[0.9BiFeO{sub 3}–0.1DyFeO{sub 3}]–xPbTiO{sub 3} (BDF–xPT) solid solution with compositions around the morphotropic phase boundary (x = 0.25, 0.28, 0.31, 0.34, and 0.37) has been synthesized in the form of ceramics. The phase symmetry, microstructure, ferroelectricity, piezoresponse, and ferromagnetic properties have been characterized by various techniques. It is found that, with increasing content of lead titanate from x = 0.25 to x = 0.37, the grain size increases and the ferroelectric property is improved. The ferroelectric performance is further enhanced by the introduction of an excess amount (2%) of TiO{sub 2} or by sintering in oxygen atmosphere, which reduces the leakage. The local polar structure is imaged by piezoresponse force microscopy. Both the out-of-plane and in-plane images reveal distinct ferroelectric domain structures, with the amplitude and the average domain size decreasing with the increase of lead titanate amount. Compared with the (1–x)BiFeO{sub 3}–xPbTiO{sub 3} binary solid solution of about the same concentration of PT, the magnetic properties are enhanced in BDF–xPT due to the presence of dysprosium, as demonstrated by the ferromagnetic hysteresis loops displayed at room temperature and at 10 K, but the remnant magnetization decreases with increasing PT content. The simultaneous presence of ferroelectricity and ferromagnetism entitles the BDF–xPT solid solution a room-temperature multiferroic material.

36 MATERIALS SCIENCE↗
DOE OSTI2011

Synthesis and Characterization of Ba(Zr{sub x}Ti{sub 1-x})O{sub 3} Solid Solutions Using Impedance Spectroscopic Techniques

Technologically important solid solutions of Ba(Zr{sub x}Ti{sub 1-x})O{sub 3} are synthesized using conventional solid state route. Relatively dense and single phase ceramics are confirmed using X-ray diffraction. Homogeneous and micron size grain growth is characterized using SEM. Impedance spectroscopy is used to study the electrical properties of ceramics. Broad and diffuse impedance loss peak is observed above 250 deg. C, which shifts towards higher frequency with increase in temperature. The distribution of relaxation frequency may be associated with the B-site cationic disorder due to the random distribution of (Zr{sup 4+}/Ti{sup +4}) having different ionic radii. Impedance relaxation obeys the Arrhenius relation with activation energy, E{tau} is 0.31 eV and 0.48 eV for BZT compositions with x = 0.10 and 0.15 respectively. Equivalent circuit representation using two RC element coupled in parallel is used to analyse the impedance response.

36 MATERIALS SCIENCE↗