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All sourcesNASA NTRSDOE OSTI
DOE OSTI2018

Multiscale analysis of nanoindentation-induced defect structures in gum metal

Using ex-situ transmission electron microscopy and the recently developed nanoprobe diffraction (NPD) technique, we characterize a nanoindented solution treated gum metal. Lattice rotations are resolved at a 1.2 nm length-scale and shown to be continuous within the nanoindentation pit; further, it is revealed that these can be accommodated by a reasonable number of geometrically necessary dislocations at a density of ~10 15 /m 2 . We furthermore provide direct evidence that dislocations within the nanoindent, rather than secondary phase nanoparticles, can serve as potent barriers to dislocation motion. We also demonstrate that plasticity in these alloys under nanoindentation can be accommodated solely by dislocation nucleation and propagation, with no competing deformation mechanisms present. Conventional transmission electron microscopy and “ g•b ” analysis reveal the presence of dislocations on &lang;$ \bar{1}11 $&rang;{110} slip systems and highly localized plastic deformation in the form of shear bands on <111>{$ \bar{1} \bar{1}2 $} slip systems, similar to previously observed “giant faults”.

36 MATERIALS SCIENCE↗
DOE OSTI2019

X-ray diffraction, Mössbauer spectroscopy, neutron diffraction, optical absorption and ab-initio calculation of magnetic process in orthorhombic YFe x Cr (1-x) O 3 (0 ≤ x ≤ 1) compounds

YFe x Cr (1-x) O 3 (0 ≤ x ≤ 1) compounds prepared by autocombustion were studied with X-ray and neutron powder diffraction, Mössbauer spectroscopy and ab-initio electronic structure calculations to try to understand the interplay of magnetic order and structural parameters as a function of doping in this multiferroic material. All samples exhibit the orthorhombic nuclear structure (space group symmetry Pnma) and the cell parameters vary continuously as a function of doping. In the neutron powder diffraction patterns it was observed that in addition to the Pnma nuclear structure peaks reflections are seen in all samples which arise from magnetic order. These peaks can be indexed using the nuclear unit cell indicating an ordering vector of k = (0,0,0). Using representational analysis and Rietveld refinements the magnetic structure was determined to be Pn’ma’ and the mean magnetic moment per transition metal atom was observed to decrease continuously from Fe to Cr. For compounds with x > 0.25 a weak ferromagnetic contribution is also present which is due to a small canting of the moments out of the basal plane. The Mössbauer spectra corroborate the NPD results with all samples showing single magnetic sextets at 4.2 K. The energy gap and the main direct interband transition of the endmember samples were obtained by optical absorption measurements. These optical data were analyzed with the help of DFT band structure calculation using the GGA-PBE + U approximation.

Salazar-Rodriquez, Roberto↗
DOE OSTI2020

Unraveling the nature of Fe-doping mediated inter- and intra-chain interactions in Ca 3 Co 2 O 6

The structural and magnetic properties of quasi-one-dimensional (1D) spin-chain compounds Ca 3 Co 2-x Fe x O 6 (x = 0, 0.1, 0.2 and 0.3) synthesized by a sol-gel method have been systematically studied by means of X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), neutron powder diffraction (NPD), dc and ac magnetization measurements. The samples adopt a rhombohedral crystal structure with the space group R-3c in a temperature range of 5–100 K. Fe ions are found to locate at the trigonal prism Co2 crystallographic sites. Fe doping converts some of low-spin Co 3+ ions at Co1 octahedral sites into Co 2+ ions. For the high-temperature paramagnetic phase, the Curie paramagnetic temperature θp changes its sign from positive to negative at x = 0.2, implying that the dominant magnetic interaction is driven from ferromagnetic (FM) to antiferromagnetic (AFM) upon Fe substitution. A partial low-spin to high-spin state crossover of the Co1 ions is observed at high Fe-doping level x = 0.3. All the samples exhibit a long-range spin-density wave (SDW) AFM ordering below TN, followed by a spin-glass-like transition at Tf. These low-temperature magnetic phases were significantly suppressed upon Fe doping. The Fe substitution in Ca 3 Co 2-x Fe x O 6 weakened both intrachain and interchain magnetic interactions, caused by enhanced magnetic disorder due to the different magnetic characters of Ising Co and Heisenberg Fe spins.

36 MATERIALS SCIENCE↗
DOE OSTI2022

Understanding the effect of salt concentrations on fast charging performance of Li-ion cells

Here, different lithium salt (lithium bis(fluorosulfonyl) imide (LiFSI)/LiPF 6 9/1 mol ratio) concentrations in carbonate electrolyte were studied on the fast charging performance of LiNi 0.6 Mn 0.2 Co 0.2 O 2 (NMC622)/graphite pouch cells. The cells with electrolyte concentration from 0.75 M to 1.50 M showed similar fast charging capabilities. Further increase of the concentration to 1.75 M and 2.00 M decreased the attainable capacity in fast charging. In the long-term cycling test, the capacity retention after 200 fast charging cycles increased with the increase of salt concentration in electrolyte. Cells with 1.5 M electrolyte showed the best overall performance in fast charging capacity and long-term cycling. Li platings were observed in the cells with 0.75 M, 1.00 M and 1.25 M electrolyte. It was improved with greatly reduced Li plating area in 1.50 M, and no Li plating at all in 1.75 M and 2.00 M electrolyte. Post-mortem analysis such as neutron powder diffraction (NPD) and X-ray photoelectron spectroscopy (XPS) were used to characterize the electrode after cycling. It suggests that electrolyte concentration needs to be optimized for a given cell configuration with specific electrode and loading.

25 ENERGY STORAGE↗
DOE OSTI2012

A study of the crystal structures and the phase transitions of the ordered double perovskites Sr{sub 2}ScSbO{sub 6} and Ca{sub 2}ScSbO{sub 6}

The crystal structures and phase transitions of the two ordered double perovskites Sr{sub 2}ScSbO{sub 6} and Ca{sub 2}ScSbO{sub 6} were studied using conventional X-ray and neutron powder-diffraction methods. The crystal structures of both compounds have the P2{sub 1}/n space group symmetry at room temperature, resulting from Sc/Sb ordering. The evolution with temperature of the structure of the Sr containing compound shows the presence of three phase transitions with the following sequence: P2{sub 1}/n{yields}I2/m{yields}I4/m{yields}Fm3{sup Macron }m, at about 400, 560 and 650 K, respectively. The smaller size of Ca cation, with respect to that of Sr cation, leads to a large distortion of Ca{sub 2}ScSbO{sub 6} at room temperature. This fact in turn causes that the Ca containing compound shows only the first phase transition from P2{sub 1}/n to I2/m at high temperature at about 1440 K. The analysis of the phase transitions and the refinements have done using the symmetry-adapted modes and the tools of the Bilbao Crystallographic Server. - Graphical abstract: Representation of the new structure resulting from the coupling of the unidimensional GM{sup 4+} and X{sup 3+} modes with the a{sup +}b{sup -}b{sup -} tilting scheme associated to P2{sub 1}/n and the temperature evolution of the amplitudes of the GM{sup 1+}, GM{sup 3+}, GM{sup 4+} and GM{sup 5+} modes of I2/m and I4/m space groups obtained from the NPD data of Sr{sub 2}ScSbO{sub 6}. Highlights: Black-Right-Pointing-Pointer Study of two compounds of the antimony double perovskite family. Black-Right-Pointing-Pointer Determination of the structures at room temperature. Black-Right-Pointing-Pointer Determination of high-temperature phase transitions by X-ray and neutron powder diffraction. Black-Right-Pointing-Pointer Using the symmetry-adapted modes to study the phase transitions.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2013

Synthesis, structural and magnetic characterisation of the fully fluorinated compound 6H-BaFeO{sub 2}F

The compound 6H-BaFeO{sub 2}F (P6{sub 3}/mmc) was synthesised by the low temperature fluorination of 6H-BaFeO{sub 3-d} using polyvinylidenedifluoride (PVDF) as a fluorination agent. Structural characterisation by XRD and NPD suggests that the local positions of the oxygen and fluorine atoms vary with no evidence for ordering on the anion sites. This compound shows antiferromagnetic ordering at room temperature with antiparallel alignment of the magnetic moments along the c-axis. The use of PVDF also allows the possibility of tuning the fluorine content in materials of composition 6H-BaFeO{sub 3-d}F{sub y} to any value of 0<y{<=}1. In addition, the oxygen content, and therefore the iron oxidation state, can be tuned by applying different partial pressures of oxygen during the reaction. - Graphical abstract: The crystal structure of the hexagonal perovskite phase 6H-BaFeO{sub 2}F. Highlights: Black-Right-Pointing-Pointer The crystal structure of the hexagonal perovskite phase 6H-BaFeO{sub 2}F. Black-Right-Pointing-Pointer H-BaFeO{sub 2}F and 6H-BaFeO{sub 3-d}F{sub y} were prepared via low temperature fluorination using PVDF. Black-Right-Pointing-Pointer A structural investigation of the compounds BaFeO{sub 2}F is presented in detail. Black-Right-Pointing-Pointer This analysis suggests differences for the local coordination of O{sup 2-} and F{sup -} anions. Black-Right-Pointing-Pointer H-BaFeO{sub 2}F shows antiferromagnetic ordering at 300 K. Black-Right-Pointing-Pointer The magnetic moments align parallel to the a-axis.

36 MATERIALS SCIENCE↗
DOE OSTI2013

Investigation of an unusual low-temperature phase transformation in RbBH{sub 4} by neutron diffraction

To investigate the previously reported low-temperature phase transition in rubidium borohydride (RbBH{sub 4}) near 48.5 K, we carried out neutron powder diffraction and vibrational spectroscopy measurements both above and below this temperature on an isotopically-enriched sample of Rb{sup 11}BD{sub 4}. Our diffraction data reflected an average cubic Fm3{sup ¯}m structure with BD{sub 4}{sup −} anion orientational disorder at all temperatures, with no hint of extra Bragg peaks due to long-range orientational order below the transition temperature as reported by others. These structural results and careful analysis of torsional vibrations in RbBD{sub 4} corroborate the results of prior neutron vibrational spectroscopy measurements suggesting that the low-temperature RbBH{sub 4} structure indeed possesses some orientational ordering of the BH{sub 4}{sup −} anions, but of a shorter-ranged nature insensitive to powder diffraction methods. - The neutron powder diffraction pattern of RbBD{sub 4} below the phase transition temperature (shown here in black) is indistinguishable from that collected above the phase transition temperature. The inset depicts the cubic structure that fits the data at both temperatures. - Highlights: • We investigated the nature of the RbBD{sub 4} phase transition using NVS and NPD. • A change in shape of the RbBD{sub 4} torsion mode was observed across the transition. • The RbBD{sub 4} diffraction pattern across this phase transition was unchanged. • The phase transition in RbBD{sub 4} appears to produce only short-range ordering of BD{sub 4}{sup −}.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2013

Lifting the geometric frustration through a monoclinic distortion in “114” YBaFe{sub 4}O{sub 7.0}: Magnetism and transport

The possibility to lift the geometric frustration in the “114” stoichiomeric tetragonal oxide YBaFe{sub 4}O{sub 7.0} by decreasing the temperature has been investigated using neutron and synchrotron powder diffraction techniques. Besides the structural transition from tetragonal to monoclinic symmetry that appears at T{sub S}=180 K, a magnetic transition is observed below T{sub N}=95 K. The latter corresponds to a lifting of the 3D geometric frustration toward an antiferromagnetic long range ordering, never observed to date in a cubic based “114’” oxide. The magnetic structure, characterized by the propagation vector k{sub 1}=(0,0,½), shows that one iron Fe2 exhibits a larger magnetic moment than the three others, suggesting a possible charge ordering according to the formula YBaFe{sup 3+}Fe{sub 3}{sup 2+}O{sub 7.0}. The magnetic M(T) and χ′(T) curves, in agreement with neutron data, confirm the structural and magnetic transitions and evidence the coexistence of residual magnetic frustration. Moreover, the transport measurements show a resistive transition from a thermally activated conduction mechanism to a variable range hopping mechanism at T{sub S}=180 K, with a significant increase of the dependence of the resistivity vs. temperature. Mössbauer spectroscopy clearly evidences a change in the electronic configuration of the iron framework at the structural transition as well as coexistence of several oxidation states. The role of barium underbonding in these transitions is discussed. - Graphical abstract: Atomic displacements at the tetragonal-monoclinic transition in YBaFe{sub 4}O{sub 7}. Display Omitted - Highlights: • The structural and magnetic phase transitions of YBaFe{sub 4}O{sub 7} were studied below room temperature. • The tetragonal to monoclinic transition, characterized by NPD and SXRD, was studied using mode crystallography approach. • Monoclinic distortion allows the lifting of the geometrical frustration on the iron sublattice, leading to AF order at T=95 K.

36 MATERIALS SCIENCE↗
DOE OSTI2013

Designing new n=2 Sillen–Aurivillius phases by lattice-matched substitutions in the halide and [Bi{sub 2}O{sub 2}]{sup 2+} layers

A new n=2 Sillen–Aurivillius compound Bi{sub 3}Sr{sub 2}Nb{sub 2}O{sub 11}Br has been synthesised based on Bi{sub 3}Pb{sub 2}Nb{sub 2}O{sub 11}Cl by simultaneously replacing Pb{sup 2+} with Sr{sup 2+} and Cl{sup −} with Br{sup −}. Rietveld refinements against X-ray and neutron powder diffraction data revealed a significant relative compression in the stacking axis (c-axis) of the new compound. Sr{sup 2+} doping reduces the impact of the stereochemically active 6s{sup 2} lone pair found on Pb{sup 2+} and Bi{sup 3+}, resulting in a contraction of the c-axis by 1.22% and an expansion of the ab plane by 0.25%. This improves the inter-layer compatibility with the larger halide Br{sup −}. Analysis of X-ray absorption near-edge spectroscopy data show that the ferroelectric distortion of the B-site cation is less apparent in Bi{sub 3}Sr{sub 2}Nb{sub 2}O{sub 11}Br compared to Bi{sub 3}Pb{sub 2}Nb{sub 2}O{sub 11}Cl, and variable-temperature neutron diffraction data show no evidence for a ferroelectric distortion. - Graphical abstract: The structural expansion and contractions in the stacking axis of co-doped Sillen–Aurivillius phases. Display Omitted - Highlights: • A new Sillen–Aurivillius phase Bi{sub 3}Sr{sub 2}Nb{sub 2}O{sub 11}Br is synthesised based on Bi{sub 3}Pb{sub 2}Nb{sub 2}O{sub 11}Cl. • The stacking axis contracts although local expansion accommodates the larger halide Br. • Majority of the contraction is observed in the [Bi{sub 2}O{sub 2}]{sup 2+} layers where we replaced Pb{sup 2+} for Sr{sup 2+}. • Removing the Pb{sup 2+} lowers the lone pair effect and improves inter-layer compatibility. • XANES and NPD suggest that the ferroelectric properties are minimised or suppressed.

36 MATERIALS SCIENCE↗
DOE OSTI2015

Structural and magnetic properties of RTiNO{sub 2} (R=Ce, Pr, Nd) perovskite nitride oxides

Neutron powder diffraction indicates that CeTiNO{sub 2} and PrTiNO{sub 2} crystallize with orthorhombic Pnma symmetry (Ce: a=5.5580(5), b=7.8369(7), and c=5.5830(4) Å; Pr: a=5.5468(5), b=7.8142(5), and c=5.5514(5) Å) as a result of a{sup –}b{sup +}a{sup –} tilting of the titanium-centered octahedra. Careful examination of the NPD data, confirms the absence of long range anion order in both compounds, while apparent superstructure reflections seen in electron diffraction patterns provide evidence for short range anion order. Inverse magnetic susceptibility plots reveal that the RTiNO{sub 2} (R=Ce, Pr, Nd) compounds are paramagnetic with Weiss constants that vary from −28 to −42 K. Effective magnetic moments for RTiNO{sub 2} (R=Ce, Pr, Nd) are 2.43 μ{sub B}, 3.63 μ{sub B}, and 3.47 μ{sub B}, respectively, in line with values expected for free rare-earth ions. Deviations from Curie–Weiss behavior that occur below 150 K for CeTiNO{sub 2} and below 30 K for NdTiNO{sub 2} are driven by magnetic anisotropy, spin–orbit coupling, and crystal field effects. - Graphical abstract: The structure and magnetism of the oxide nitride perovskites RTiNO{sub 2} (R=Ce, Pr, Nd) have been explored. The average symmetry is shown to be Pnma with a random distribution of oxide and nitride ions and a{sup −}b{sup +}a{sup −} tilting of the titanium-centered octahedra, but electron diffraction shows evidence for short range anion order. All three compounds are paramagnetic but deviations from the Curie Weiss law are seen below 150 K for R=Ce and below 30 K for R=Nd. - Highlights: • The oxide nitride perovskites RTiNO{sub 2} (R=Ce, Pr) have been prepared and their structures determined. • Diffraction measurements indicate short range cis-order of O and N, but no long range order. • Compounds are paramagnetic with Weiss constants that vary from −28 to −42 K. • CeTiO{sub 2}N and NdTiO{sub 2}N deviate from Curie–Weiss behavior below 150 and 30 K, respectively.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2016

Structural and spectroscopic studies of Ba{sub 2}Y{sub 1−δ}UO{sub 6+x}

A combination of S-XRD and NPD demonstrate the structure of Ba{sub 2}Y{sub 0.879}UO{sub 6+x} to be monoclinic in space group I2/m. That the U is hexavalent is evident from the U L{sub 2}-edge XANES measurements. This appears to be a rare example of a double perovskite containing vacancies at the octahedral B-sites and interstitial oxygen defects, which combine to stabilise hexavalent U and appears to be a consequence of the preparation of the sample in air. The Y vacancies, coupled with anion disorder, results in a distortion of the BO{sub 6} octahedra. - Graphical abstract: The structure of Ba{sub 2}Y{sub 0.879}UO{sub 6+x} is shown to be a rare example of a double perovskite containing vacancies at the octahedral B-sites and interstitial oxygen defects. - Highlights: • Structure of Ba{sub 2}Y{sub 0.879}UO{sub 6+x} refined. • U L-edge XANES demonstrates the U is hexavalent. • Rare example of a perovskite containing vacancies at the octahedral B-site. • Y vacancies result in a distortion of the BO{sub 6} octahedra.

36 MATERIALS SCIENCE↗
DOE OSTI2012

Synthesis and characterisation of the novel double perovskites La{sub 2}CrB{sub 2/3}Nb{sub 1/3}O{sub 6}, B = Mg, Ni, Cu

Highlights: ► La{sub 2}CrB{sub 2/3}Nb{sub 1/3}O{sub 6}, B = Mg, Ni, Cu perovskites adopt the GdFeO{sub 3} type structure. ► HREM and ED study indicating week ordering of B-cations for B = Mg. ► Antiferromagnetics with T{sub N} 90 (Mg), 125 (Ni) and 140 K (Ni). -- Abstract: The novel perovskites La{sub 2}CrB{sub 2/3}Nb{sub 1/3}O{sub 6}, B = Mg, Ni, and Cu have been synthesised at 1350 °C in air via the citrate route. Rietveld refinements using neutron powder diffraction (NPD) data showed that the compounds adopt the GdFeO{sub 3} type structure with space group Pbnm, and unit cell parameters a≈b≈√(2)×a{sub p} and c ≈ 2 × a{sub p}, where a{sub p} ≈ 3.8 Å. Selected area electron diffraction (SAED) of B = Ni and Cu samples confirmed space group Pbnm. However, distinct reflections forbidden in Pbnm symmetry, but allowed in the monoclinic sub-group P2{sub 1}/n and unit cell parameters a≈b≈√(2)×a{sub p} and c ≈ 2 × a{sub p}, β ≈ 90° were present in SAED patterns of B = Mg sample. This indicates an ordering of the B-cations within the crystal structure of La{sub 2}CrMg{sub 2/3}Nb{sub 1/3}O{sub 6}. High-resolution electron microscopy (HREM) study indicating uniform, without formation of clusters, ordering of B-cations in the crystallites of La{sub 2}CrMg{sub 2/3}Nb{sub 1/3}O{sub 6}. Magnetic susceptibility measurements show that the compounds are antiferromagnetic (with some glass or spin clustering effects due to additional ferromagnetic interactions between the B-cations) with T{sub N} for La{sub 2}CrB{sub 2/3}Nb{sub 1/3}O{sub 6}, B = Mg, Ni, Cu being 90, 125 and 140 K, respectively.

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 OSTI2015

Cationic ordering and role of the B-site lanthanide(III) and molybdenum(V) cations on the structure and magnetism of double perovskites Sr{sub 2}LnMoO{sub 6}

Highlights: • Five new double perovskites of formula Sr{sub 2}LnMoO{sub 6} were synthesized. • All the samples crystallize in the monoclinic P2{sub 1}/n space group. • Strong reducing conditions were used in order to stabilized Mo(V) cations. • A complete ordering between the rare earth and molybdenum ions was observed. • Magnetism agrees with the crystal distortions observed from Rietveld analysis. - Abstract: We describe the preparation, crystal structure determination and magnetic properties of a new series of ordered double perovskite oxides Sr{sub 2}LnMoO{sub 6} (Ln = Eu, Gd, Dy, Ho, Er, Yb) with Mo{sup 5+} and Ln{sup 3+} electronic configurations. These compounds have been obtained by solid state reaction under reducing conditions in order to stabilize Mo{sup 5+} cations. Structural characterization by XRPD and NPD was performed when Ln = Ho, Er, Yb and just XRPD for absorbing Ln = Eu, Gd, Dy. At room temperature, an excellent Rietveld fit was obtained for all the samples in a monoclinic symmetry, space group P2{sub 1}/n, with long-range ordering of Ln and Mo atoms. Magnetic susceptibility measurements show that some of these materials present magnetic ordering below 25 K and the determined effective magnetic moments are consistent with those expected for the pair Ln{sup 3+}–Mo{sup 5+}. All the phases have negative values​​ of the Weiss temperature indicating dominance of antiferromagnetic interactions.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Synthesis and structural characterization of the vividly colored first row transition metal-containing oxyfluoride antiperovskites Sr3-xMnxMO4F and Sr3-xMnxMO4-αF1-δ (M = Al, Ga)

Highlights: • Substitution of Mn{sup 2+} demonstrates Sr{sub 3-x}A{sub x}MO{sub 4}F can tolerate divalent first row transition metals. • The colors of these materials vary from green to purple depending on anion stoichiometry. • Intense colors are likely due to small amounts of Mn{sup 3+} on the tetrahedral Al site. • Structural data is consistent with preferential occupation of eight-coordinate Sr(2) site by Mn{sup 2+}. • Large off-center displacements are observed on the underbonded ten-coordinate Sr(1) site. - Abstract: Incorporation of dopant amounts of the divalent transition metal cation Mn{sup 2+} into the oxyfluoride material Sr{sub 3-x}Mn{sub x}MO{sub 4}F (M = Al, Ga; 0 ≤ x ≤ 0.1) yields green powders which vary in hue depending on the identity of M. Treatment of these phases with post-synthesis annealing under reducing conditions produces anion deficient phases according to Sr{sub 3-x}Mn{sub x}MO{sub 4-α}F{sub 1-δ} displaying vivid purple coloration. Intense colors are likely due to small amounts of Mn{sup 3+} on the tetrahedral M site. Full structural characterization based upon powder X-ray diffraction (PXRD), neutron powder diffraction (NPD), and thermogravimetric analysis (TGA) data are presented herein, demonstrating that the Sr{sub 3-x}A{sub x}MO{sub 4}F (A = Ca, Sr, Ba; M = Al, Ga) anti-perovskite structure can readily accommodate first row transition metals.

36 MATERIALS SCIENCE↗
DOE OSTI2021

The surface triple-coupling on single crystalline cathode for lithium ion batteries

Single crystalline (SC) cathode materials, which are less susceptible to micro/nano-cracks formation and offer better structure stability compared to the polycrystalline counterpart, have attained great attention. However, the parasitic side reactions at the cathode-electrolyte interface induces the loss of active species, which consequently leads to continual degradation of the electrochemical performances. Herein, a triple coupling of concentration-gradient Na+, F- co-doping and surface NaF coating are exploited for the first time on SC LiNi 0.5C o 0.2 Mn 0.3 O 2 cathode by the hydrolysis of NaPF 6 . This process regulates the external structure of materials by constructing a “sandwich” configuration from surface to bulk: rock salt - mixing zone - layered phase. The detailed interface transformation mechanism is revealed by Neutron powder diffraction (NPD), spherical aberration corrected high-resolution scanning transmission electron microscopy (HR-STEM), electron energy loss spectroscopy (EELS), and Ar+ sputtering assisted X-ray photoelectron spectroscopy (XPS). The synergistic effects endow the SC cathode with outstanding capacity retentions: 91.3% at 25 °C and 85% at 45 °C, after 500 cycles at 5 C between 3.0 and 4.5 V. In addition, a high full-cell reversible capacity of 168.9 mAh g -1 with a capacity retention of 92.4% is achieved after 300 cycles at 1 C. Multiple characterizations further indicate that these superior results are mainly ascribed to the overall structure integrity of SC material, the thin cathode electrolyte interface, high content of lithium fluoride, and the low solubility of transition metal ions. This work opens a new avenue to construct a benign interface towards high-performance lithium ion batteries.

lithium ion batteries↗
DOE OSTI2013

Near independence of OLED operating voltage on transport layer thickness

We report organic light emitting devices (OLEDs) with weak drive voltage dependence on the thickness of the hole transport layer (HTL) for thicknesses up to 1150 Å using the N,N'-Bis(naphthalen-1-yl)-N,N'-bis(phenyl)-benzidine (α-NPD) and N,N'-bis(3-methyl phenyl)-N,N'-diphenyl-[1,1'-biphenyl]-4,4'diamine (TPD), both of which have hole mobilities in the range of 2 × 10-3 cm2V-1s-1. Lower mobility HTL materials show larger operating voltage dependence on thickness. The near independence of the operating voltage for high mobility transport material thickness was only observed when the energy barrier for charge injection into the transport material was minimized. To ensure low injection barriers, a thin film of 2-(3-(adamantan-1-yl)propyl)-3,5,6-trifluorotetracyanoquinodimethane (F3TCNQ-Adl) was cast from solution onto the ITO surface. These results indicate that thick transport layers can be integrated into OLED stacks without the need for bulk conductivity doping.

30 DIRECT ENERGY CONVERSION↗
DOE OSTI2018

Crystal Structures, Local Atomic Environments, and Ion Diffusion Mechanisms of Scandium-Substituted Sodium Superionic Conductor (NASICON) Solid Electrolytes

The importance of exploring new solid electrolytes for all-solid-state batteries has led to significant interest in NASICON-type materials. In this work, the Sc 3+ -substituted NASICON compositions Na 3 Sc x Zr 2– x (SiO 4 ) 2- x (PO 4 ) 1+ x (termed N3) and Na 2 Sc y Zr 2- y (SiO 4 ) 1- y (PO 4 ) 2+ y (termed N2) ( x , y = 0–1) are studied as model Na + -ion conducting electrolytes for solid-state batteries. The influence of Sc 3+ substitution on the crystal structures and local atomic environments has been characterized by powder X-ray diffraction (XRD) and neutron powder diffraction (NPD), as well as solid-state 23 Na, 31 P, and 29 Si nuclear magnetic resonance (NMR) spectroscopy. A phase transition between 295 and 473 K from monoclinic C 2/ c to rhombohedral $R\bar{3}c$ is observed for the N3 compositions, while N2 compositions crystallize in a rhombohedral $R\bar{3}c$ unit cell in this temperature range. Alternating current (AC) impedance spectroscopy, molecular dynamics (MD), and high temperature 23 Na NMR studies are in good agreement, showing that, with a higher Sc 3+ concentration, the ionic conductivity (of about 10 -4 S/cm at 473 K) decreases and the activation energy for ion diffusion increases. 23 Na NMR experiments indicate that the nature of the Na + -ion motion is two-dimensional on the local atomic scale of NMR although the long-range diffusion pathways are three-dimensional. In addition, a combination of MD, bond valence, maximum entropy/Rietveld, and van Hove correlation methods has been used to reveal that the Na + -ion diffusion in these NASICON materials is three-dimensional and that there is a continuous exchange of sodium ions between Na(1) and Na(2) sites.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗