Synchrotron Radiation Powder X-ray Diffraction Research Articles

Chloride substitution in sodium borohydride

The dissolution of sodium chloride and sodium borohydride into each other resulting in formation of solid solutions of composition Na(BH 4) 1− x Cl x is studied. The dissolution reaction is facilitated by two methods: ball milling or combination of ball milling and annealing at 300 °C for three days of NaBH 4–NaCl samples in molar ratios of 0.5:0.5 and 0.75:0.25. The degree of dissolution is studied by Rietveld refinement of synchrotron radiation powder X-ray diffraction (SR-PXD) data. The results show that dissolution of 10 mol% NaCl into NaBH 4, forming Na(BH 4) 0.9Cl 0.1, takes place during ball milling. A higher degree of dissolution of NaCl in NaBH 4 is obtained by annealing resulting in solid solutions containing up to 57 mol% NaCl, i.e. Na(BH 4) 0.43Cl 0.57. In addition, annealing results in dissolution of 10–20 mol% NaBH 4 into NaCl. The mechanism of the dissolution during annealing and the decomposition pathway of the solid solutions are studied by in situ SR-PXD. Furthermore, the stability upon hydrogen release and uptake were studied by Sieverts measurements.

Thermal Expansion of Oxyarsenides (LaO)TAs; T = Transition Metal

We have investigated the precise crystal structure and their temperature dependences of oxyarsenides (LaO)TAs; T = Mn, Fe, Co, as the Fe based superconductor’s parent material family using high energy synchrotron radiation x-ray powder diffraction. Lattice constants a and c decrease with decreasing temperature. Focusing the ratios of the changes normalized by room temperature lattice constants, we have found anisotropic shrinks for the superconductor’s parent material of (LaO)FeAs and the ferromagnetic metal (LaO)CoAs. The shrinkage of the lattice constant c along the stacking direction will be discussed by the temperature dependence of the divided three components of the LaO layer, TAs layer, and the interlayer distance.

Anion Substitution in Ca(BH4)2−CaI2: Synthesis, Structure and Stability of Three New Compounds

The substitution of the complex borohydride anion BH4− in calcium borohydride by the larger iodide anion I− is explored in order to tailor the hydrogen storage properties. Three new compounds are identified in the Ca(BH4)2−CaI2 system and are structurally characterized using the Rietveld method and synchrotron radiation powder X-ray diffraction (SR-PXD) data. Calcium borohydride readily dissolves in the trigonal calcium iodide structure during ball milling, forming a solid solution Ca((BH4)1−xIx)2 with a CaI2-type structure and an anisotropically contracted trigonal unit cell, a = 4.311(1) and c = 6.867(2) A for x ∼ 0.3 (T = 28 °C), space group P3m1. The trigonal tri-Ca((BH4)0.70I0.30)2 transforms at ∼180 °C to an orthorhombic phase of similar composition, ort-Ca((BH4)0.64I0.36)2, with a CaCl2-type structure (a distorted β-Ca(BH4)2 type structure) and cell parameters a = 7.271(2), b = 7.042(1), and c = 4.4601(7) A (T = 322 °C), space group Pnnm. Further heating of the CaCl2-type compound to ∼330 °C leads...

Experimental charge density of LiBD4from maximum entropy method

We report on maximum entropy method study of the experimental atomic and ionic charges of LiBD4 in its low-temperature orthorhombic phase. Synchrotron radiation x-ray powder diffraction data, neutron powder diffraction data, and density functional calculations were used. The atomic and ionic charges were determined for both experimental and theoretical results using the Bader analysis for atoms in molecules. The charge transfer from the Li cation to the BD4 anion is 0.86(+/- 9) e, which is in good agreement with the ab initio calculated value of 0.895 e. The experimental accuracy was determined considering the differences between results obtained for data collected at 10 and 90 K, different experimental setups (high-resolution diffractometer or image plate diffractometer), and different structural models used for the prior density distributions needed for accurate maximum entropy calculations (refined using only synchrotron radiation x-ray powder diffraction data or combined with neutron powder diffraction data).

Ca(BH4)2−MgF2 Reversible Hydrogen Storage: Reaction Mechanisms and Kinetic Properties

A composite of Ca(BH4)2−MgF2 is proposed as a reversible hydrogen storage system. The dehydrogenation and rehydrogenation reaction mechanisms are investigated by in situ time-resolved synchrotron radiation powder X-ray diffraction (SR-PXD) and Raman spectroscopy. The formation of an intermediate phase (CaF2−xHx) is observed during rehydrogenation. The hydrogen content of 4.3 wt % is obtained within 4 h during the first dehydrogenation at isothermal and isobaric conditions of 330 °C and 0.5 bar H2, respectively. The cycling efficiency is evaluated by three release and uptake cycles together with absorbed hydrogen content in the range 5.1−5.8 wt % after 2.5 h (T = 330 °C and p(H2) = 130 bar). The kinetic properties on the basis of hydrogen absorption are comparable for all cycles. As compared to pure Ca(BH4)2 and Ca(BH4)2−MgH2 composite, Ca(BH4)2−MgF2 composite reveals the kinetic destabilization and the reproducibility of hydrogen storage capacities during cycling, respectively.

High-Temperature and High-Pressure Aqueous Solution Formation, Growth, Crystal Structure, and Magnetic Properties of BiFeO3 Nanocrystals

In situ synchrotron radiation powder X-ray diffraction (SR-PXRD) was applied to study the formation and growth of BiFeO3 nanocrystals, revealing that phase pure BiFeO3 can be obtained in high-temperature, high-pressure aqueous solution using Bi(NO3)3 and Fe(NO3)3·9H2O as precursors and KOH as mineralizer. The method gives a rapid way for preparation of nanomaterials, and the formation of BiFeO3 can be finished within seconds after its initial nucleation in near-critical aqueous solution. As proof of concept BiFeO3 nanocrystals were subsequently synthesized in a continuous flow supercritical system and for reference also in autoclaves. High resolution multitemperature SR-PXRD data were measured between 100 and 1000 K with a step size of 100 K. The magnetic properties of both the autoclave and the continuous flow samples are studied.

Effect of Transition Metal Fluorides on the Sorption Properties and Reversible Formation of Ca(BH4)2

Light metal borohydrides are considered as promising materials for solid state hydrogen storage. Because of the high hydrogen content of 11.5 wt % and the rather low dehydrogenation enthalpy of 32 kJ mol−1H2, Ca(BH4)2 is considered to be one of the most interesting compounds in this class of materials. In the present work, the effect of selected TM-fluoride (TM = transition metal) additives on the reversible formation of Ca(BH4)2 was investigated by means of thermovolumetric, calorimetric, Fourier transform infrared spectroscopy, and ex situ, and in situ synchrotron radiation powder X-ray diffraction (SR-PXD) measurements. Furthermore, selected desorbed samples were analyzed by 11B{1H} solid state magic angle spinning nuclear magnetic resonance (MAS NMR). Under the conditions used in this study (145 bar H2 pressure and 350 °C), TiF4 and NbF5 were the only additives causing partial reversibility. In these two cases, 11B{1H} MAS NMR analyses detected CaB6 and likely CaB12H12 in the dehydrogenation products....

The crystal structure of the first borohydride borate, Ca3(BD4)3(BO3)

The previously observed intermediate from thermal decomposition of Ca(BH4)2 has been identified as a calcium borohydride borate with composition Ca3(11BD4)3(11BO3), synthesized from a double-isotope substituted sample Ca(11BD4)2. The crystal structure was determined on the basis of Synchrotron Radiation Powder X-ray Diffraction, supported by infrared spectroscopy measurements. The stability of the structure at ambient conditions is confirmed by Density Functional Theory calculations. Ca3(11BH4)3(11BO3) is the first example of a product from a borohydride oxidation containing both B–H(D) and B–O bonds and represents a novel category of compounds, being completely different from the hydroxoborate products upon borohydride hydrolysis. The result represents hence an important contribution to fundamental boron chemistry.

PLUXter: Rapid Discovery of Metal-Organic Framework Structures Using PCA and HCA of High Throughput Synchrotron Powder Diffraction Data

This paper reports on a systematic method--called PLUXter--developed for screening and data mining of large numbers of potential metal-organic framework compounds that have been synthesized then subsequently analyzed with high throughput synchrotron radiation X-ray powder diffraction. The first part of the method utilizes principal components analysis (PCA), which allows materials to be ranked in order of crystallinity so that undesirable amorphous materials may be identified and eliminated. The second part allows structural grouping within and between samples to be observed using hierarchical cluster analysis (HCA). Classification using a single linkage distance produced unsatisfactory clusters however the dendrogram's structural relationships were used to establish and guide the boundaries of groups. The resultant grouping identities allowed further structure-property studies to be undertaken on representative structures from the clusters, significantly reducing time and the use of resources.

Observation of Dipole Stripes and Domain Structure by Transmission Electron Microscope for BiFeO3 Single Crystals

The BiFeO3 single crystals were grown in air in a Bi2O3/Fe2O3 flux. X-ray microanalysis, high resolution synchrotron radiation powder X-ray diffraction, and selected area electron diffraction pattern showed that these single crystals are high quality and exhibit a rhombohedral R3c structure. The dipole stripes and the complex domains of spontaneous ferroelectric polarization had been observed for the first time using HRTEM technique. This work will facilitate intuitive understanding of the atomic scale spontaneous ferroelectric polarization domain structure and of the impact of defects and oxygen vacancies on magnetic and dielectric properties.

Structure and Characterization of KSc(BH4)4

A new potassium scandium borohydride, KSc(BH4)4, is presented and characterized by a combination of in situ synchrotron radiation powder X-ray diffraction, thermal analysis, and vibrational and NMR spectroscopy. The title compound, KSc(BH4)4, forms at ambient conditions in ball milled mixtures of potassium borohydride and ScCl3 together with a new ternary chloride K3ScCl6, which is also structurally characterized. This indicates that the formation of KSc(BH4)4 differs from a simple metathesis reaction, and the highest scandium borohydride yield (∼31 mol %) can be obtained with a reactant ratio KBH4:ScCl3 of 2:1. KSc(BH4)4 crystallizes in the orthorhombic crystal system, a = 11.856(5), b = 7.800(3), c = 10.126(6) A, V = 936.4(8) A3 at RT, with the space group symmetry Pnma. KSc(BH4)4 has a BaSO4 type structure where the BH4 tetrahedra take the oxygen positions. Regarding the packing of cations, K+, and complex anions, [Sc(BH4)4]−, the structure of KSc(BH4)4 can be seen as a distorted variant of orthorhombi...

Hydrogen storage and phase transformations in Mg–Pd nanoparticles

Microstructure refinement and synergic coupling among different phases are currently explored strategies to improve the hydrogen storage properties of traditional materials. In this work, we apply a combination of these methods and synthesize Mg–Pd composite nanoparticles by inert gas condensation of Mg vapors followed by vacuum evaporation of Pd clusters. Irreversible formation of the Mg6Pd intermetallic phase takes place upon vacuum annealing, resulting in Mg/Mg6Pd composite nanoparticles. Their hydrogen storage properties are investigated and connected to the undergoing phase transformations by gas-volumetric techniques and in situ synchrotron radiation powder x-ray diffraction. Mg6Pd transforms reversibly into different Mg–Pd intermetallic compounds upon hydrogen absorption, depending on temperature and pressure. In particular, at 573 K and 1 MPa hydrogen pressure, the metal-hydride transition leads to the formation of Mg3Pd and Mg5Pd2 phases. By increasing the pressure to 5 MPa, the Pd-richer MgPd intermetallic is obtained. Upon hydrogen desorption, the Mg6Pd phase is reversibly recovered. These phase transformations result in a specific hydrogen storage capacity associated with Mg–Pd intermetallics, which attain the maximum value of 3.96 wt % for MgPd and influence both the thermodynamics and kinetics of hydrogen sorption in the composite nanoparticles.

Crystal structure of quenched and in-field electroluminescent phosphors

Electroluminescent zinc sulfide doped with copper and chloride (ZnS:Cu, Cl) powder was heated to 400°C and rapidly quenched to room temperature. Comparison between the quenched and non-quenched phosphors using synchrotron radiation X-ray powder diffraction (XRPD) (λ = 0.828692 Å) and X-ray absorption spectroscopy (XAS) was made. XRPD shows that the expected highly faulted structure is observed with excellent resolution out to 150° 2θ (or to (12 2 2) of the sphalerite phase). The quenched sample compared to the unheated sample shows a large change in peak ratios between 46.7° and 46.9°, which is thought to correspond to the wurtzite (0 0 6), (0 3 2) and sphalerite (3 3 3)/(5 1 1) peaks. Hence, a large proportion of this sphalerite diffraction is lost from the material upon rapid quenching, but not when the material is allowed to cool slowly. The Zn K-edge XAS data indicate that the crystalline structures are indistinguishable using this technique, but do give an indication that the electronic structure has altered due to changing intensity of the white line. It is noted that the blue electroluminescence (EL) emission bands are lost upon quenching: however, a large amount of total EL emission intensity is also removed, which is consistent with our findings. We report the XRPD of a working alternating-current electroluminescence device in the synchrotron X-ray beam, which exhibits a new diffraction pattern when the device is powered in an AC field even though the phosphor is fixed in the binder. Significantly, only a few crystals are required to yield the diffraction data because of the high flux X-ray source. These in panel data show multiple sharp diffraction lines spread out under the region, where capillary data show broad diffraction intensity indicating that the phosphor powder is comprised of unique crystals, each having different structures.

Thermal Polymorphism and Decomposition of Y(BH4)3

The structure and thermal decomposition of Y(BH(4))(3) is studied by in situ synchrotron radiation powder X-ray diffraction (SR-PXD), (11)B MAS NMR spectroscopy, and thermal analysis (thermogravimetric analysis/differential scanning calorimetry). The samples were prepared via a metathesis reaction between LiBH(4) and YCl(3) in different molar ratios mediated by ball milling. A new high temperature polymorph of Y(BH(4))(3), denoted beta-Y(BH(4))(3), is discovered besides the Y(BH(4))(3) polymorph previously reported, denoted alpha-Y(BH(4))(3). beta-Y(BH(4))(3) has a cubic crystal structure and crystallizes with the space group symmetry Pm3m and a bisected a-axis, a = 5.4547(8) A, as compared to alpha-Y(BH(4))(3), a = 10.7445(4) A (Pa3). Beta-Y(BH(4))(3) crystallizes with a regular ReO(3)-type structure, hence the Y(3+) cations form cubes with BH(4)(-) anions located on the edges. This arrangement is a regular variant of the distorted Y(3+) cube observed in alpha-Y(BH(4))(3), which is similar to the high pressure phase of ReO(3). The new phase, beta-Y(BH(4))(3) is formed in small amounts during ball milling; however, larger amounts are formed under moderate hydrogen pressure via a phase transition from alpha- to beta-Y(BH(4))(3), at approximately 180 degrees C. Upon further heating, beta-Y(BH(4))(3) decomposes at approximately 190 degrees C to YH(3), which transforms to YH(2) at 270 degrees C. An unidentified compound is observed in the temperature range 215-280 degrees C, which may be a new Y-B-H containing decomposition product. The final decomposition product is YB(4). These results show that boron remains in the solid phase when Y(BH(4))(3) decomposes in a hydrogen atmosphere and that Y(BH(4))(3) may store hydrogen reversibly.

Tuning hydrogen storage properties and reactivity: Investigation of the LiBH 4–NaAlH 4 system

Tuning the hydrogen storage properties of complex metal hydrides is of vast interest. Here, we investigate the hydrogen release and uptake pathways for a reactive hydride composite, LiBH 4−NaAlH 4 utilizing in situ synchrotron radiation powder X-ray diffraction experiments. Sodium alanate transforms to sodium borohydride via a metathesis reaction during ball milling or by heating at T∼95 °C. NaBH 4 decomposes at ∼340 °C in dynamic vacuum, apparently directly to solid amorphous boron and hydrogen and sodium gas and the latter two elements are lost from the sample. Under other conditions, T=400 °C and p(H 2)=∼1 bar, NaBH 4 only partly decomposes to B and NaH. On the other hand, formation of LiAl is facilitated by dynamic vacuum conditions, which gives access to the full hydrogen contents in the LiBH 4−NaAlH 4 system. Formation of AlB 2 is observed ( T∼450 °C) and other phases, possibly AlB x or Al 1− x Li x B 2, were observed for the more Li-rich samples. This may open new routes to the stabilization of boron in the solid state in the dehydrogenated state, which is a challenging and important issue for hydrogen storage systems based on borohydrides.

Crystal structure, polymorphism, and thermal properties of yttrium borohydride Y(BH 4) 3

Y(BH 4) 3 was synthesized by cryo-milling mixtures of LiBH 4 and YCl 3 and characterized by powder X-ray and neutron diffraction (PXD, PND), differential scanning calorimetry (DSC), and temperature programmed desorption (TPD). The crystal structure was refined in the space group Pa−3 (no. 205) with lattice constant a = 10.8522(7) Å from 11B and D ( 2H) substituted samples using PND. It was found to contain Y 3+ cations in a highly distorted octahedral environment formed by six [BD 4] − complex anions. Heat treatment under 10 MPa of deuterium at 475 K led to a phase transformation from the primitive cubic room-temperature phase to a face-centered cubic high-temperature phase with space group Fm−3 c (no. 226) and lattice constant a = 11.0086(1) Å. This high-temperature phase shows an ideal and undistorted octahedral coordination around the central Y 3+ cation. In situ synchrotron radiation powder X-ray diffraction experiments (SR-PXD) show the presence of an intermediate phase during the thermal decomposition of Y(BH 4) 3 with presumably orthorhombic symmetry, and lattice constants a = 12.170(14) Å, b = 7.670(5) Å, and c = 7.478 (6) Å, in a narrow temperature region between 473 K and 520 K.

Synthesis and decomposition mechanisms of Mg 2FeH 6 studied by in-situ synchrotron X-ray diffraction and high-pressure DSC

Synthesis and decomposition mechanisms of ternary Mg 2FeH 6 were investigated using in-situ synchrotron radiation powder X-ray diffraction (SR-PXD) and high-pressure differential scanning calorimetry (HP-DSC). Two routes for synthesis of Mg 2FeH 6 were studied. The first utilizes a ball-milled homogeneous MgH 2–Fe powder mixture and the second uses a mixture of Fe and Mg formed by decomposition of the ternary hydride, Mg 2FeH 6. In both cases the reaction mixture was sintered in a temperature range from RT to 500 °C under a hydrogen pressure of 100–120 bar. The reaction mechanisms were established using in-situ SR-PXD. The formation of Mg 2FeH 6 consists of two steps with MgH 2 as an intermediate compound, and the presence of magnesium was not observed. In contrast, the decomposition of Mg 2FeH 6 was found to be a single-step reaction. Additionally, both reactions were investigated using HP-DSC under similar conditions as in the SR-PXD experiments in order to estimate reaction enthalpies and temperatures. Mg 2FeH 6 was found to form from MgH 2 and Fe under hydrogen pressure regardless of whether the MgH 2 was introduced in the mixture or formed prior to creation of the ternary hydride.

Structural variations in nanosized confined gallium

The complex crystalline structure of gallium under nanoconfinement was revealed by synchrotron radiation x-ray powder diffraction. Nanoconfinement was shown to stabilize δ-Ga which is metastable in bulk. Two new gallium phases named ι- and κ-Ga were found upon cooling below room temperature. These crystalline modifications were stable and coexisted with known gallium phases. Correlations between confined gallium particle shapes and emergence of particular crystalline phases were observed. Melting and freezing temperatures for different gallium phases were obtained. Remarkable supercooling of liquid gallium was seen in 3.5 nm pores.

NaSc(BH4)4: A Novel Scandium-Based Borohydride

A new alkaline transition-metal borohydride, NaSc(BH4)(4), is presented. The compound has been studied using a combination of in situ synchrotron radiation powder X-ray diffraction, thermal analysis, and vibrational and NMR spectroscopy. NaSc(BH4)(4) forms at ambient conditions in ball-milled mixtures of sodium borohydride and ScCl3. A new tertiary chloride Na3ScCl6 (P2(1)/n, a = 6.7375(3) angstrom, b = 7.1567(3) angstrom, c = 9,9316(5) angstrom, beta = 90.491(3)degrees, V = 478.87(4) angstrom(3)), isostructural to Na3TiCl6, was identified as an additional phase in all samples. This indicates that the formation of NaSc(BH4)(4) differs from a simple metathesis reaction, and the highest scandium borohydride yield (22 wt %) was obtained with a reactant ratio of ScCl3/NaBH4 of 1:2. NaSc(BH4)(4) crystallizes in the orthorhombic crystal system with the space group symmetry Cmcm (a = 8.170(2) angstrom, b = 11.875(3) angstrom, c = 9.018(2) angstrom, V = 874.9(3) angstrom(3)). The Structure of NaSc(BH4)(4) consists of isolated homoleptic scandium tetraborohydride anions, [Sc(BH4)(4)](-), located inside slightly distorted trigonal Na-6 prisms (each second prism is empty, triangular angles of 55.5 and 69.1 degrees). The experimental results show that each Sc3+ is tetrahedrally Surrounded by four BH4 tetrahedra with a 12-fold coordination of H to Sc, while Na+ is surrounded by six BH4 tetrahedra in a quite regular octahedral coordination with a (6 + 12)-fold coordination of H to Na. The packing of Na+ cations and [Sc(BH)(4))(4)](-) anions in NaSc(BH4)(4) is a deformation variant of the hexagonal NiAs structure type. NaSc(BH4)(4) is stable from RT up to similar to 410 K, Where the compound melts and then releases hydrogen in two rapidly occurring steps between 440 and 490 K and 495 and 540 K. Thermal expansion of NaSc(BH4)(4) between RT and 408 K is anisotropic, and lattice parameter b shows strong anomaly close to the melting temperature.

Structure and Dynamics for LiBH4−LiCl Solid Solutions

A surprisingly high degree of structural and compositional dynamics is observed in the system LiBH4−LiCl as a function of temperature and time. Rietveld refinement of synchrotron radiation powder X-ray diffraction (SR-PXD) data reveals that Cl− readily substitutes for BH4− in the structure of LiBH4. Prolonged heating a sample of LiBH4−LiCl (1:1 molar ratio) above the phase transition temperature and below the melting point (108 < T < 275 °C) can produce highly chloride substituted hexagonal lithium borohydride, h-Li(BH4)1−xClx, e.g., x ∼ 0.42, after heating from room temperature (RT) to 224 °C at 2.5 °C/min. LiCl has a higher solubility in h-LiBH4 as compared to orthorhombic lithium borohydride, o-LiBH4, which is illustrated by a LiBH4−LiCl (1:1) sample equilibrated at 245 °C for 24 days and left at RT for another 13 months. Rietveld refinement reveals that this sample contains o-Li(BH4)0.91Cl0.09 and LiCl. This illustrates a significantly faster dissolution of LiCl in h-LiBH4 as compared to a slower segregation of LiCl from o-LiBH4, which is also demonstrated by in situ SR-PXD from three cycles of heating and cooling of the same Li(BH4)0.91Cl0.09 sample. The substitution of the smaller Cl− for the larger BH4− ion is clearly observed as a reduction in the unit cell volume as a function of time and temperature. A significant stabilization of h-LiBH4 is found to depend on the degree of anion substitution. Variable temperature solid-state magic-angle spinning (MAS) 7Li and 11B NMR experiments on pure LiBH4 show an increase in full width at half maximum (fwhm) when approaching the phase transition from o- to h-LiBH4, which indicates an increase of the relaxation rate (i.e., T2 decreases). A less pronounced effect is observed for ion-substituted Li(BH4)1−xClx, 0.09 < x < 0.42. The MAS NMR experiments also demonstrate a higher degree of motion in the hexagonal phase, i.e., fwhm is reduced by more than a factor of 10 at the o- to h-LiBH4 phase transition.