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All sourcesNASA NTRSDOE OSTI
DOE OSTI2022

Real-space measurement of orbital electron populations for Li 1-x CoO 2

The operation of lithium-ion batteries involves electron removal from and filling into the redox orbitals of cathode materials, experimentally probing the orbital electron population thus is highly desirable to resolve the redox processes and charge compensation mechanism. Here, we combine quantitative convergent-beam electron diffraction with high-energy synchrotron powder X-ray diffraction to quantify the orbital populations of Co and O in the archetypal cathode material LiCoO 2 . The results indicate that removing Li ions from LiCoO 2 decreases Co t 2g orbital population, and the intensified covalency of Co–O bond upon delithiation enables charge transfer from O 2p orbital to Co e g orbital, leading to increased Co e g orbital population and oxygen oxidation. Theoretical calculations verify these experimental findings, which not only provide an intuitive picture of the redox reaction process in real space, but also offer a guidance for designing high-capacity electrodes by mediating the covalency of the TM–O interactions.

25 ENERGY STORAGE↗
NASA NTRS1996

Optimizing Process Parameters to Produce Single Phase YBa2Cu3O7 Powder

Process parameters such as temperature and time are varied to obtain single phase (pure) YBa2Cu307 powders. X-ray diffraction patterns of superconducting and nonsuperconducting powders are observed in situ in normal and elevated temperature environments to confirm known strong peaks that are unique to YBa2Cu307. Peaks vary in magnitude as a result of superconducting - nonsuperconducting phase transitions. Known strong peaks serve as our basis in monitoring transitional changes. Peak isotherms obtained experimentally are correlated with theoretical models to identify the weighting factor that characterizes the optimum isotherm. By isolating the parameters under which 100% peak growth occurs most rapidly, we obtain the optimum isotherm. The choices made for firing temperature and atmosphere were determined to be the primary factors necessary to ensure sample purity.

Hurley, J. S.↗
DOE OSTI2022

Nonequilibrium Lattice Dynamics in Photoexcited 2D Perovskites

Abstract Interplay between structural and photophysical properties of metal halide perovskites is critical to their utility in optoelectronics, but there is limited understanding of lattice response upon photoexcitation. Here, 2D perovskites butylammonium lead iodide, (BA) 2 PbI 4 , and phenethylammonium lead iodide, (PEA) 2 PbI 4 , are investigated using ultrafast transient X‐ray diffraction as a function of optical excitation fluence to discern structural dynamics. Both powder X‐ray diffraction and time‐resolved photoluminescence linewidths narrow over 1 ns following optical excitation for the fluence range studied, concurrent with slight redshifting of the optical bandgaps. These observations are attributed to transient relaxation and ordering of distorted lead iodide octahedra stimulated mainly by electron–hole pair creation. The c axis expands up to 0.37% over hundreds of picoseconds; reflections sampling the a and b axes undergo one tenth of this expansion with the same timescale. Post‐photoexcitation appearance of the (110) reflection in (BA) 2 PbI 4 would suggest a transient phase transition, however, through new single‐crystal XRD, reflections are found that violate glide plane conditions in the reported Pbca structure. The static structure space group is reassigned as P 2 1 2 1 2 1 . With this, a nonequilibrium phase transition is ruled out. These findings offer increased understanding of remarkable lattice response in 2D perovskites upon excitation.

36 MATERIALS SCIENCE↗
DOE OSTI2017

Crystal structure, homogeneity range and electronic structure of rhombohedral γ-Mn 5 Al 8

Here, the γ-region of the Mn–Al phase diagram between 45 and 70 at.% Al was re-investigated by a combination of powder and single crystal X-ray diffraction as well as EDS analysis to establish the distribution of Mn and Al atoms. Single crystals of γ-Mn 5–x Al 8+x were grown using Sn-flux at 650 °C. The crystal structure, atomic coordinates and site occupancy parameters of γ-Mn 5–x Al 8+x phases were refined from single crystal X-ray data. The γ-Mn 5-x Al 8+x phase adopts the rhombohedral Cr 5 Al 8 -type structure rather than a cubic γ-brass structure. The refined compositions from two crystals extracted from the Al-rich and Mn-rich sides are, respectively, Mn 4.76 Al 8.24(2) (I) and Mn 6.32 Al 6.68(2) (II). The structure was refined in the acentric R3m space group (No.160, Z=6), in order to compare with other reported rhombohedral γ-brasses. In addition, according to X-ray powder diffraction analysis, at the Al-rich side the γ-phase coexists with LT–Mn 4 Al 11 and, at the Mn-rich side, with a hitherto unknown phase. The refined lattice parameters from powder patterns fall in the range a=12.6814(7)–12.6012(5) Å and c=7.9444(2)–7.9311(2) Å from Al-rich to Mn-rich loadings, and the corresponding rhombohedral angles distorted from a pseudo-cubic cell were found to be 89.1(1)°–88.9(1)°. Magnetic susceptibility and magnetization studies of Mn 4.92 Al 8.08(2) are consistent with moment bearing Mn and suggest a spin glass state below 27 K. Tight-binding electronic structure calculations (LMTO-ASA with LSDA) showed that the calculated Fermi level for γ-“Mn 5 Al 8 ” falls within a pseudogap of the density of states, a result which is in accordance with a Hume-Rothery stabilization mechanism γ-brass type phases.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Compositional control of radionuclide retention in hollandite-based ceramic waste forms for Cs-immobilization

Hollandite materials, as a class of crystalline nuclear waste forms, are promising candidates for the immobilization of radioactive elements, such as Cs, Ba, as well as a variety of lanthanide and transition-metal fission products. In this study, three Ga-doped titanate hollandite-type phases, Ba 1.33 Ga 2.67 Ti 5.33 O 16 , Ba 0.667 Cs 0.667 Ga 2 Ti 6 O 16 , and Cs 1.33 Ga 1.33 Ti 6.67 O 16 , were synthesized using a solid-state reaction route. All synthesized phases adopted a single phase tetragonal structure, as determined by powder X-ray diffraction (XRD), and elemental analysis confirmed the measured stoichiometries were close to targeted compositions. Extended X-ray absorption fine structure spectroscopy (EXAFS) was used to determine the local structural features for the framework of octahedrally coordinated cations. EXAFS data indicated that Cs 1.33 Ga 1.33 Ti 6.67 O 16 possessed the most disordered local structure centered around the Ga dopant. The enthalpies of formation of all three hollandite phases measured using high-temperature oxide melt solution calorimetry were found to be negative, indicating enthalpies of formation of these hollandites from oxides are thermodynamically stable with respect to their constituent oxides. Furthermore, the formation enthalpies were more negative and hence more favorable with increased Cs content. Finally, aqueous leaching tests revealed that high Cs content hollandite phases exhibited greater Cs retention as compared to low Cs content hollandite. While preliminary in nature, this work draws attention to the links between the capacity for radionuclide retention, atomistic level structural features and bulk thermodynamic properties of materials.

nuclear (including radiation effects), materials a↗
DOE OSTI2015

A key route to designing huge eight-fold interpenetrated coordination networks with ths-type topology: Synthesis, structures, and topological characteristics

Solvothermal reactions of Cd(II) or Mn(II) ions with 4'-(4-carboxylphenyl)-2,2':6',2{sup -}terpyridine acid (Hcpt) and thiophene-2,5-dicarboxylic acid (H{sub 2}tpd) resulted in the formation of two isostructrual coordination networks ([M{sub 2}(cpt){sub 2}(tpd)]·3.5H{sub 2}O){sub n} (M=Cd, 1; M=Mn, 2). These complexes have been characterized by single-crystal X-ray diffraction analyses, infrared spectra (IR), elemental analyses, and powder X-ray diffraction (PXRD). Complexes 1 and 2, formed by the cpt{sup −} and tpd{sup 2−} bidentate connectors, have a 3D framework with a 3-connected, uninodal 10{sup 3}-ths topology possessing an unusual eight-fold [4*2] interpenetration mode. In addition, the ths cage has a long intracage M⋯M distance. In contrast, only a 1D coordination network ([CdCl(cpt)]·3.75H{sub 2}O){sub n} (3) was obtained under similar conditions while in the absence of the H{sub 2}tpd ligand. Compound 3 is propagated only by the [CdCl(cpt)] unit, which illustrated that the incorporation of the cpt{sup −} and Cl{sup −} ligands to form a 1D network. The distinct ancillary anions (tpd{sup 2−} or Cl{sup −}) play a critical role in determining the coordination features and the network connectivity of metal ions. This work presents a successful route to preparing rare eight-fold [4*2] interpenetrated networks. - Highlights: • A ths-type network with an eight-fold [4*2] interpenetration mode is rare. • Combining elongated ligands facilitate the eight-fold interpenetrated networks. • This ths-type cage features longe intracage M⋯M distances. • The chloride anion cannot help the forming of 3D frameworks. • The integration of bulky and multi-carboxylate ligands helps the forming of ths-type MOFs.

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

X-Ray diffraction on large single crystals using a powder diffractometer

Information on the lattice parameter of single crystals with known crystallographic structure allows for estimations of sample quality and composition. In many cases it is sufficient to determine one lattice parameter or the lattice spacing along a certain, high- symmetry direction, e.g. in order to determine the composition in a substitution series by taking advantage of Vegard’s rule. Here we present a guide to accurate measurements of single crystals with dimensions ranging from 200 μm up to several millimeter using a standard powder diffractometer in Bragg-Brentano geometry. The correction of the error introduced by the sample height and the optimization of the alignment are discussed in detail. Finally, in particular for single crystals with a plate-like habit, the described procedure allows for measurement of the lattice spacings normal to the plates with high accuracy on a timescale of minutes.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2014

Structural, electrical and magnetic properties of Bi{sub 0.90}La{sub 0.10}Fe{sub 0.90}Co{sub 0.10}O{sub 3} ceramics

Multiferroic Bi{sub 0.90}La{sub 0.10}Fe{sub 0.90}Co{sub 0.10}O{sub 3} ceramics have been synthesized via soft chemical co-precipitation method. From the X-ray diffraction analysis, ceramic powder sintered at 600°C was found to be single phase belonging to the rhombohedral structure with R3c space group confirmed by Rietveld analysis. Further, dielectric, Leakage and magnetic studies were performed at room temperature.

36 MATERIALS SCIENCE↗
DOE OSTI2014

MgO:Dy{sup 3+} nanophosphor: Self ignition route, characterization and its photoluminescence properties

For the first time series of MgO phosphors doped with different concentrations of Dy{sup 3+} (1–9 mol%) were prepared by solution combustion method using glycine as a fuel. The final products were well characterized by powder X-ray diffraction, Fourier transform infrared spectroscopy, scanning electron microscopy and transmission electron microscopy. The powder X-ray diffraction patterns of the as-formed product show single cubic phase. The crystallite size estimated using Scherrer's method was found to be in the range 5–15 nm and the same was confirmed by transmission electron microscopy result. Photoluminescence properties of Dy{sup 3+} (1–9 mol%) doped MgO for near ultra violet excitation (325 nm) was studied in order to investigate the possibility of its use in white light emitting diode applications. The emission spectra consists of intra 4f transitions of Dy{sup 3+}, namely {sup 4}F{sub 9/2} → {sup 6}H{sub 15/2} (483 nm), and {sup 4}F{sub 9/2} → {sup 6}H{sub 13/2} (573 nm). Further, the emission at 573 nm shows strong yellow emission and can be applied to the yellow emission of phosphor for the application for near ultraviolet excitation. The intensity of yellow emission was attributed to intrinsic defects, especially oxygen-vacancies, which could assist the energy transfer from the MgO host to the Dy{sup 3+} ions. The Commission International De I-Eclairage chromaticity co-ordinates were calculated from emission spectra, the values (x,y) were very close to the National Television System Committee standard value of white emission. Therefore, the present phosphor was highly useful for display applications. - Graphical Abstract: PL emission spectra and CIE diagram of MgO:Dy{sup 3+} nanophosphor. - Highlights: • MgO:Dy{sup 3+} prepared by simple and low cost LCS method at low temperature (400 °C). • Characteristic emission peaks of Dy{sup 3+} ion at ∼ 483 and 573 nm are recorded. • CIE co-ordinate values located in the white region. • Present phosphor was quite useful for display applications.

36 MATERIALS SCIENCE↗
DOE OSTI2014

Crystal structure of a birefringent andradite-grossular from Crowsnest Pass, Alberta, Canada

The structure of a birefringent andradite–grossular sample was refined using single-crystal X-ray diffraction (SCD) and synchrotron high-resolution powder X-ray diffraction (HRPXRD) data. Electron-microprobe results indicate a homogeneous composition of {Ca 2.88 Mn 2+ 0.06 Mg 0.04 Fe 2+ 0.03 } Σ3 [Fe 3+ 1.29 Al 0.49 Ti 4+ 0.17Fe 2+ 0.06 ] Σ2 (Si 2.89 Al 0.11 ) Σ3 O 12 . The Rietveld refinement reduced χ 2 = 1.384 and overall R (F 2 ) = 0.0315. The HRPXRD data show that the sample contains three phases. For phase-1, the weight %, unit-cell parameter (Å), distances (Å), and site occupancy factor (sof) are 62.85(7)%, a = 12.000 06(2), average = 2.4196, Fe–O = 1.9882(5), Si–O = 1.6542(6) Å, Ca(sof) = 0.970(2), Fe(sof) = 0.763(1), and Si(sof) = 0.954(2). The corresponding data for phase-2 are 19.14(9)%, a = 12.049 51(2), average = 2.427, Fe–O = 1.999(1), Si–O = 1.665(1) Å, Ca(sof) = 0.928(4), Fe(sof) = 0.825(3), and Si(sof) = 0.964(4). The corresponding data for phase-3 are 18.01(9)%, a = 12.019 68(3), average = 2.424, Fe–O = 1.992(2), Si–O = 1.658(2) Å, Ca(sof) = 0.896(5), Fe(sof) = 0.754(4), and Si(sof) = 0.936(5). The fine-scale coexistence of the three phases causes strain that arises from the unit-cell and bond distances differences, and gives rise to strain-induced birefringence. The results from the SCD are similar to the dominant phase-1 obtained by the HRPXRD, but the SCD misses the minor phases.

Antao, Sytle M.↗
DOE OSTI2015

Hydrothermal synthesis and characterization of a two-dimensional piperazinium cobalt–zinc phosphate via a metastable one-dimensional phase

A two-dimensional piperazinium cobalt–zinc phosphate, formulated as (C{sub 4}N{sub 2}H{sub 12}){sub 1.5}(Co{sub 0.6}Zn{sub 0.4}){sub 2}(HPO{sub 4}){sub 2}(PO{sub 4})·H{sub 2}O (2D), was synthesized under hydrothermal conditions. The crystal structure was determined using single-crystal X-ray diffraction data (monoclinic P2{sub 1}/c, a=8.1165(3) Å, b=26.2301(10) Å, c=8.3595(4) Å, and β=110.930(5)°) and the hydrogen atom positions were optimized by DFT calculations. A single-crystal corresponding to one-dimensional metastable phase, (C{sub 4}N{sub 2}H{sub 12})Co{sub 0.3}Zn{sub 0.7}(HPO{sub 4}){sub 2}·H{sub 2}O (1D), was also isolated and the crystal structure was determined (monoclinic P2{sub 1}/c, a=8.9120(6) Å, b=14.0290(1) Å, c=12.2494(5) Å, and β=130.884(6)°). The bulk was characterized by chemical (C–H–N) analysis, powder X-ray diffraction (PXRD), powder X-ray thermodiffractometry (HT-XRD), transmission electron microscopy (STEM(DF)-EDX and EFTEM), and thermal analysis (TG/SDTA-MS), including activation energy data of its thermal decomposition. The magnetic susceptibility and magnetization measurements show no magnetic ordering down to 4 K. - Graphical abstract: Hydrothermal synthesis and structural characterization of a two-dimensional piperazinium cobalt–zinc phosphate, (C{sub 4}N{sub 2}H{sub 12}){sub 1.5}(Co{sub 0.6}Zn{sub 0.4}){sub 2}(HPO{sub 4}){sub 2}(PO{sub 4})·H{sub 2}O (2D), have been reported. The crystal structure of a one-dimensional piperazinium cobalt–zinc phosphate, (C{sub 4}N{sub 2}H{sub 12})Co{sub 0.3}Zn{sub 0.7}(HPO{sub 4}){sub 2}·H{sub 2}O (1D) a metastable phase during the hydrothermal synthesis, was also determined. The thermal behavior of 2D compound is strongly dependent on the selected heating rate and the magnetic susceptibility and magnetization measurements show no magnetic ordering down to 4 K. - Highlights: • A 2D piperazinium cobalt–zinc phosphate has been synthesized and characterized. • Crystal structure of 1D metastable phase was also determined. • Thermal behavior of 2D compound is strongly dependent on the selected heating rate. • Magnetic measurements show no magnetic ordering down to 4 K.

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

Crystal structures of the new ternary stannides La{sub 3}Mg{sub 4−x}Sn{sub 2+x} and LaMg{sub 3−x}Sn{sub 2}

Synthesis and structural characterization of the two new lanthanum–magnesium–stannides La{sub 3}Mg{sub 4−x}Sn{sub 2+x} (0.12≤x≤0.40) and LaMg{sub 3−x}Sn{sub 2} (0.33≤x≤0.78) are reported. The crystal structures of these intermetallics were determined by single crystal X-ray diffraction analysis and confirmed by Rietveld refinement of powder X-ray diffraction patterns of the corresponding samples. The La{sub 3}Mg{sub 4−x}Sn{sub 2+x} phase crystallizes in the hexagonal Zr{sub 3}Cu{sub 4}Si{sub 2} structure type (P6¯2m, hP9, Z=3, x=0.12(1), a=7.7974(7), c=4.8384(4) Å), which represents an ordered derivative of the hP9-ZrNiAl prototype, ubiquitous among equiatomic intermetallics. The LaMg{sub 3–x}Sn{sub 2} phase is the second representative of the trigonal LaMg{sub 3−x}Ge{sub 2} type, which is a superstructure of the LaLi{sub 3}Sb{sub 2} structure type (P3¯1c, hP34-0.12, Z=6, x=0.35(1), a=8.3222(9), c=14.9546(16) Å). The scheme describing the symmetry reduction/coloring with respect to the parent type is reported here with the purpose to discuss the LaMg{sub 3−x}Sn{sub 2} off-stoichiometry from the geometrical point of view. Structural relationships between the La–Mg–Sn ternary phases, including the already known equiatomic LaMgSn compound (oP12-TiNiSi), are presented in the framework of the AlB{sub 2}-related compounds family and discussed with the aid of group-subgroup relations in the Bärnighausen formalism. - Graphical abstract: Crystal structure of LaMg{sub 3−x}Sn{sub 2} viewed along the (001) direction together with the puckered layer of Mg and Sn atoms hosting Mg2, Mg3 and vacancy □. - Highlights: • Crystal structures of the new La{sub 3}Mg{sub 4−x}Sn{sub 2+x} and LaMg{sub 3−x}Sn{sub 2} phases were determined. • The off-stoichiometry of LaMg{sub 3−x}Sn{sub 2} was discussed from geometrical point of view. • Structural relations between the known La–Mg–Sn phases were established. • The studied compounds are related to the AlB{sub 2} type by symmetry reduction.

36 MATERIALS SCIENCE↗
DOE OSTI2015

Preparation and characterisation of nanoscale α-Al{sub 2}O{sub 3} by precipitation method

Nanometer-scale α-Al{sub 2}O{sub 3} particles have been synthesized by a simple precipitation method from an aqueous solution in the presence of AlCl{sub 3} and NH{sub 3}. The surface morphology and composition of the as-synthesized Al{sub 2}O{sub 3} nanoparticle were characterized by means of scanning electron microscopy (SEM) and X-ray diffraction (XRD). The powder was nanocrystalline in nature having hexagonal structure with unit cell parameters: a=4.76A°, c=12.99A°. The Al{sub 2}O{sub 3} nanocrystallites with an average crystal size of about 86 nm. The powder has been characterized by means of FT-IR, and UV-Vis Study. From these results it is possible to conclude that the precipitation method is a very suitable technique to prepare α-Al{sub 2}O{sub 3} materials. The technique is fast, low cost and produces well defined materials that can be used for dosimetric applications.

36 MATERIALS SCIENCE↗
DOE OSTI2015

The application of inelastic neutron scattering to explore the significance of a magnetic transition in an iron based Fischer-Tropsch catalyst that is active for the hydrogenation of CO

An iron based Fischer-Tropsch synthesis catalyst is evaluated using CO hydrogenation at ambient pressure as a test reaction and is characterised by a combination of inelastic neutron scattering (INS), powder X-ray diffraction, temperature-programmed oxidation, Raman scattering, and transmission electron microscopy. The INS spectrum of the as-prepared bulk iron oxide pre-catalyst (hematite, α-Fe{sub 2}O{sub 3}) is distinguished by a relatively intense band at 810 cm{sup −1}, which has previously been tentatively assigned as a magnon (spinon) feature. An analysis of the neutron scattering intensity of this band as a function of momentum transfer unambiguously confirms this assignment. Post-reaction, the spinon feature disappears and the INS spectrum is characterised by the presence of a hydrocarbonaceous overlayer. A role for the application of INS in magnetic characterisation of iron based FTS catalysts is briefly considered.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2017

Investigation of the commensurate magnetic structure in the heavy-fermion compound CePt 2 In 7 using magnetic resonant x-ray diffraction

In this paper, we investigated the magnetic structure of the heavy-fermion compound CePt 2 In 7 below T N = 5.34 (2) K using magnetic resonant x-ray diffraction at ambient pressure. The magnetic order is characterized by a commensurate propagation vector k 1/2 = (1/2, 1/2, 1/2) with spins lying in the basal plane. Our measurements did not reveal the presence of an incommensurate order propagating along the high-symmetry directions in reciprocal space but cannot exclude other incommensurate modulations or weak scattering intensities. The observed commensurate order can be described equivalently by either a single-k structure or by a multi-k structure. Furthermore we explain how a commensurate-only ordering may explain the broad distribution of internal fields observed in nuclear quadrupolar resonance experiments [Sakai et al., Phys. Rev. B 83, 140408 (2011)] that was previously attributed to an incommensurate order. We also report powder x-ray diffraction showing that the crystallographic structure of CePt 2 In 7 changes monotonically with pressure up to P = 7.3 GPa at room temperature. The determined bulk modulus B 0 = 81.1 (3) GPa is similar to those of the Ce-115 family. Broad diffraction peaks confirm the presence of pronounced strain in polycrystalline samples of CePt 2 In 7 . Lastly, we discuss how strain effects can lead to different electronic and magnetic properties between polycrystalline and single crystal samples.

36 MATERIALS SCIENCE↗
DOE OSTI2015

Crystal growth, differential gas adsorption, high thermal stability, and reversible coordination of two new barium-organic frameworks, Ba(SBA)(DMF){sub 4} and Ba{sub 2}(BTEC)(H{sub 2}O)

Single crystals of two barium-organic framework materials, Ba(SBA)(DMF){sub 4} (CAUMOF-15) and Ba{sub 2}(BTEC)(H{sub 2}O) (CAUMOF-16), have been grown through solvothermal reactions (H{sub 2}SBA=4,4′-sulfonyldibenzoic acid and H{sub 4}BTEC=1,2,4,5-benzenetetracarboxylic acid). The crystal structures of the reported frameworks have been determined by single-crystal X-ray diffraction. The materials have been fully characterized by powder X-ray diffraction (PXRD), elemental analyses, Infrared (IR) spectroscopy, and thermogravimetric analyses (TGA). CAUMOF-15 reveals a three-dimensional open-framework that comprises of an inorganic motif with one-dimensional chains and the SBA linkers. CAUMOF-16 shows another three-dimensional backbone consisting of layers of edge-shared BaO{sub 9} and BaO{sub 10} polyhedra, and BTEC pillars. Both of the 3D frameworks exhibit relatively high thermal stabilities. The PXRD and IR spectral data confirm that CAUMOF-15 and CAUMOF-16 reveal reversible coordinations of the respective solvent molecules, DMF and H{sub 2}O. Gas adsorption properties towards nitrogen, hydrogen, and carbon dioxide have been also investigated. - Graphical abstract: Crystals of two new barium-organic frameworks, Ba(SBA)(DMF){sub 4} and Ba{sub 2}(BTEC)(H{sub 2}O), exhibiting a differential gas adsorption, a high thermal stability, and a reversible coordination of solvent molecules have been grown. - Highlights: • Crystals of two new 3D Ba-MOFs are grown. • The two Ba-MOFs reveal very high thermal stabilities up to ca. 400 °C. • Ba(SBA)(DMF){sub 4} exhibits differential gas adsorption properties. • The two Ba-MOFs show reversible coordination of the solvent molecules.

36 MATERIALS SCIENCE↗
DOE OSTI2014

Experimental Evidence of Negative Linear Compressibility in the MIL-53 Metal-Organic Framework Family

Here, we report a series of powder X-ray diffraction experiments performed on the soft porous crystals MIL-53(Al) and NH 2 -MIL-53(Al) in a diamond anvil cell under different pressurization media. Systematic refinements of the obtained powder patterns demonstrate that these materials expand along a specific direction while undergoing total volume reduction under an increasing hydrostatic pressure. Our results confirm for the first time the negative linear compressibility behaviour of this family of materials, recently predicted from quantum chemical calculations.

36 MATERIALS SCIENCE↗
DOE OSTI2014

Observation of localized heating phenomena during microwave heating of mixed powders using in situ x-ray diffraction technique

In materials processing research using microwave heating, there have been several observations of various phenomena occurring known as microwave effects. One significant example of such a phenomenon is increased reaction kinetics. It is believed that there is a possibility that this might be caused by localized heating, were some reactants would attain a higher than apparent temperature. To examine whether such thermal gradients are indeed possible, mixed powders of two microwave non-absorbers, alumina and magnesia, were mixed with graphite, a known absorber, and heated in a microwave furnace. During microwave irradiation, the local temperatures of the respective sample constituents were measured using an in situ x-ray diffraction technique. In the case of the alumina and graphite sample, a temperature difference of around 100 °C could be observed.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗