High-resolution Synchrotron X-ray Powder Diffraction Research Articles

Temperature-dependent crystal structure investigation of 4f hybridized thermoelectric clathrate Ba8-xCexAuySi46-y.

Thermoelectric materials allow for conversion of waste heat into electrical energy, and they represent a green solution for improving our energy efficiency. Inclusion of 4f electrons near the Fermi level may boost the Seebeck coefficient, which is essential for high thermoelectric performance. In this study, Ce was successfully substituted for Ba on the guest atom sites in the type-I clathrate Ba8-xCexAuySi46-y and the material was characterized using high-resolution synchrotron powder X-ray diffraction data measured from 100 K to 1000 K to investigate potential structural implications of the inclusion of a 4f element. The thermal expansion and bonding of the host structure are not affected by the presence of Ce, as seen from the linear coefficient of unit-cell thermal expansion of 7.30 (8) × 10-6 K-1 and the average host Debye temperature of 404 (7) K determined from the multi-temperature atomic displacement parameters, both of which are similar to values obtained for pure Ba8AuySi46-y. The anisotropic atomic displacement parameters on the guest atom site in the large clathrate cage populated by Ba surprisingly reveals isotropic behavior, which is different from all other clathrates reported in literature, and thus represents a unique host-guest bonding situation.

Structural Variations across Wolframite Solid Solutions, (Fe,Mn)WO4

The crystal structure of four samples from natural wolframite solid solutions, (Fe,Mn)WO4, was obtained with synchrotron high-resolution powder X-ray diffraction (HRPXRD) data, Rietveld refinements, space group P2/c, and Z = 2. Wolframite solid solutions extend from ferberite (FeWO4) to hübnerite (MnWO4). The W and (Mn,Fe) cations are in six-fold coordination. This study shows that the unit-cell parameters, a, b, c, and β angle, vary linearly with the unit-cell volume, V, across the wolframite series. The average <Mn,Fe–O> distance increases linearly because of larger Mn2+ (0.83 Å) replacing smaller Fe2+ (0.78 Å) cations, whereas the average <W–O> distance increases slightly because of the higher effective charge of the smaller Fe2+ cation. The distortions of the two types of polyhedra across the series are discussed.

Disorder-Induced Structural Complexity in the Barlowite Family of S = 1/2 Kagomé Magnets

We present a comprehensive structural and magnetic characterization of the barlowite family of S = 1/2 kagomé magnets, Cu4(OH)6FX, where X = Cl, Br, or I. Through high-resolution synchrotron X-ray and neutron powder diffraction measurements, we reveal two sources of structural complexity within this family of materials, namely, compositional disorder of the halide species that occupy sites in between the kagomé layers and the positional disorder of the interlayer Cu2+ ions that persists well into the Pnma structural ground state. We demonstrate that understanding these inherent structural disorders is key as they correlate with the degree of partial order in the magnetic ground states of these quantum frustrated magnets.

Crystal Structure of an Anisotropic Pyrope Garnet That Contains Two Cubic Phases

The crystal structure of two different samples of pyrope garnet, ideally Mg3Al2Si3O12, from South Africa was refined using the Rietveld method, space group Ia3¯d, and monochromatic synchrotron high-resolution powder X-ray diffraction (HRPXRD) data. Sample 1 from Wesselton Mine is a single cubic phase and is optically isotropic. Electron-probe microanalysis (EPMA) provided an average composition {Mg2.30Fe2+0.26Ca0.42Mn2+0.02}∑3[Al1.53Fe3+0.06Cr3+0.40Ti4+0.01Fe2+0.01]∑2Si3O12, which contains a significant amount of Cr cations. The unit-cell parameter (Å) and bond distances (Å) are a = 11.56197(1) Å, average <Mg-O> = 2.2985, Al-O = 1.9101(4), and Si-O = 1.6343(3) Å. Sample 2 from De Beers Diamond Mine has an average composition {Mg2.33Fe2+0.33Ca0.33Mn2+0.01}∑3[Al1.73Fe3+0.12Cr3+0.06Ti4+0.05Fe2+0.05]∑2Si3O12 and is a fine-scale intergrowth of two cubic phases. The weight percentage, unit-cell parameter (Å), and bond distances (Å) for phase 2a are 62.2(1)%, a = 11.56185(1) Å, average <Mg-O> = 2.3006, Al-O = 1.9080(4), Si-O = 1.6334(4) Å. The corresponding values for phase 2b are 37.8(1)%, a = 11.53896(1) Å, average <Mg-O> = 2.2954, Al-O = 1.9020(6), Si-O = 1.6334(6) Å. The two cubic phases in sample 2 cause the crystal to be optically anisotropic because of strain induce birefringence. The unit-cell parameter and bond distances for sample 1 are similar to those in phase 2a.

Structure determination of riboflavin by synchrotron high-resolution powder X-ray diffraction

The crystal structure of the stable form of vitamin B2 or riboflavin (C17H20N4O6) was solved using high-resolution powder X-ray diffraction (PXRD). The high-resolution PXRD pattern of riboflavin was recorded at room temperature at the European Synchrotron Radiation Facility (Grenoble, France). The starting structural model was generated using a Monte Carlo simulated annealing method. The final structure was obtained through Rietveld refinement. The positions of the H atoms belonging to hydroxy groups were estimated from computational energy minimizations. The symmetry is orthorhombic with the space group P212121 and the following lattice parameters: a= 20.01308, b= 15.07337 and c= 5.31565 Å.

Formation, thermal redox reaction and crystal structure of δ-CaCr2O4

The thermal redox reactions of a Ca–Cr–O system under different atmospheric conditions were investigated by cyclic thermodiffractometry and thermogravimetry. In the first heating process under a reductive atmosphere, CaCrO4 decomposed into CaO and δ-CaCr2O4, a metastable form, with the liberation of free oxygen. In the second process under an oxidizing atmosphere, the CaO and δ-CaCr2O4 produced in the first reduction process reacted to regenerate CaCrO4, indicating that this redox reaction could proceed reversibly upon controlling the atmosphere. The crystal structure of δ-CaCr2O4 was determined, for the first time, on the basis of high-resolution synchrotron powder X-ray diffraction data. δ-CaCr2O4 crystallized in a monoclinic structure with the space group P21/m. The structure can be described as a stacking of CrO2 layers composed of edge-sharing CrO6 octahedra, with calcium ions residing on-site between the layers. The calcium ions were coordinated by six oxygen atoms to form a trigonal prism geometry between the CrO2 layers. The structure of δ-CaCr2O4 was different from those of low-temperature β-CaCr2O4 (distorted CaFe2O4-type) and high-temperature α-CaCr2O4 (P2-type layered structure).

Metal-organic framework-derived carbon nanotubes with multi-active Fe-N/Fe sites as a bifunctional electrocatalyst for zinc-air battery

Sustainable metal-air batteries demand high-efficiency, environmentally-friendly, and non-precious metal-based electrocatalysts with bifunctionality for both the oxygen reduction reaction (ORR) and oxygen evolution reaction (OER). In this research, novel functional carbon nanotubes with multi-active sites including well-dispersed single-atom iron throughout the walls and encapsulated ultrafine iron nanoparticles were synthesized as an electrocatalyst (FeNP@Fe-N-C) through one-step pyrolysis of metal-organic frameworks. High-resolution synchrotron powder X-ray diffraction and X-ray absorption spectroscopy were applied to characterize the unique structure of the electrocatalyst. In comparison to the commercial Pt/C and RuO2 electrodes, the newly prepared FeNP@Fe-N-C presented a superb bifunctional performance with its narrow potential difference (Egap) of 0.73 V, which is ascribed to the metallic Fe nanoparticles that boosts the adsorption and activation of oxygen on the active sites with an enhanced O2 adsorption capacity of 7.88 cm3 g−1 and synergistically functionalizes the iron atoms dispersed on the nanotubes. A rechargeable zinc-air battery based on FeNP@Fe-N-C exhibited a superior open-circuit voltage (1.45 V), power density (106.5 mW cm−2), and stable cycling performance. The green technique developed in this work for the fabrication of functional nanotubes raises the prospect of making more efficient electrocatalysts for sustainable energy cells.

Crystal Chemistry of Six Grossular Garnet Samples from Different Well-Known Localities

Two isotropic grossular (ideally Ca3Al2Si3O12) samples from (1) Canada and (2) Tanzania, three optically anisotropic grossular samples (3, 4, 5) from Mexico, and one (6) anisotropic sample from Italy were studied. The crystal structure of the six samples was refined in the cubic space group Ia3¯d, using monochromatic synchrotron high-resolution powder X-ray diffraction (HRPXRD) data and the Rietveld method. The compositions of the samples were obtained from electron microprobe analyses (EPMA). The HRPXRD traces show a single cubic phase for two isotropic samples, whereas the four anisotropic samples contain two different cubic phases that were also resolved using X-ray elemental line scans, backscattered electron (BSE) images, and elemental maps. Structural mismatch from two cubic phases intergrown in the birefringent samples gives rise to strain-induced optical anisotropy. Considering the garnet general formula, [8]X3[6]Y2[4]Z3[4]O12, the results of this study show that with increasing unit-cell parameter, the Y-O distance increases linearly and rather steeply, the average <X-O> distance increases just slightly in response to substitution mainly on the Y site, while the Z-O distance remains nearly constant. The X and Z sites in grossular contain Ca and Si atoms, respectively; both sites show insignificant substitutions by other atoms, which is supported by a constant Z-O distance and only a slight increase in the average <X-O> distance. The main cation exchange is realized in the Y site, where Fe3+ (ionic radius = 0.645 Å) replaces Al3+ (ionic radius = 0.545 Å), so the Y-O distance increases the most.

Magnetic ground state and crystal structure of the giant dielectric constant material Ba(Fe1/2Nb1/2)O3

The room temperature crystal structure as well as the magnetic ground state of Ba(Fe1/2Nb1/2)O3 (BFN) are controversial. The results of Rietveld refinements using high-resolution synchrotron x-ray powder diffraction (SXRPD) data are presented to show that BFN belongs to cubic perovskite structure in the Pm3¯m space group and not in the cubic Fm3¯m or monoclinic symmetries, proposed by some earlier workers based on the analysis of the laboratory source XRD data. The temperature dependent specific heat measurements in the 1.8 to 300 K range on well characterized BFN samples are presented to show the absence of any long-range ordered (LRO) antiferromagnetic (AFM) transition, proposed by some earlier workers based on the observation of a peak in the temperature dependence of zero-field cooled (ZFC) DC magnetization around 25 to 32 K. Results of temperature dependent magnetization measurements during warming cycle on ZFC and field cooled (FC) BFN samples reveal history dependent bifurcation with a peak in the ZFC M (T) curve at Tf ~ 29 K, in agreement with some previous results where it was attributed to a spin-glass transition even though such an irreversibility can result from superparamagnetic (SPM) blocking as well. The appearance of a short plateau in our FC M (T) curve below Tf suggests a cluster spin-glass phase of BFN below Tf. This was confirmed by us through the ac susceptibility χ' (T, ω) studies which reveal divergence of spin dynamics at the spin-glass transition temperature TSG ~ (28 ± 1) K with a large characteristic spin relaxation time τ0 ~ 10−6 s following Vogel-Fulcher as well as power-law type critical dynamics. The existence of the magnetic glassy state in BFN is further supported by the observation of (1) magnetic field dependent shift of Tf with increasing magnetic field along the de Almeida-Thouless line in the T-H plane with a characteristic exponent of m = 2/3, (2) weak remanent magnetization Mr below Tf with exponentially decreasing Mr on approaching Tf, (3) extremely slow decay of the thermoremanent magnetization below Tf with time as per a stretched exponential function, and (4) characteristic aging, rejuvenation and memory effects below Tf. These results provide the first unambiguous confirmation of the cluster spin-glass state of BFN and settle the existing controversies related to its magnetic ground state.

Compositional pathways and anisotropic thermal expansion of high-entropy transition metal diborides

The recent discovery of high entropy transition metal diborides (HEBs) has sparked renewed interest in ultra-high temperature ceramics (UHTCs). Presently, transition metal (Me) oxides based boro-carbo/thermal reduction (BCTR) syntheses show great promise as relatively cheap production methods, but also may present limits to attain single phase pure HEBs. Herein, by selectively tuning the concentration of boron and carbon, the reducing agents of Me oxide mixture (Me = Ti, Ta, Nb, Zr and Hf), and exploiting high-resolution synchrotron X-ray powder diffraction, we first identified and quantified the formation of intermediate phases during the BCTR synthesis, with the ultimate intent to achieve a full dense (Ti,Ta,Nb,Zr,Hf)B2 solid solution (SS). Additional insight was obtained by temperature dependent diffraction, which highlighted, for the first time in this class of materials, anisotropic thermal expansion, most likely at the origin of the SS micro-cracking, as was also observed by electron microscopy.

Acoustic levitation and high-resolution synchrotron X-ray powder diffraction: A fast screening approach of niclosamide amorphous solid dispersions

The levitation of samples in an acoustic field has been of interest in the preparation and study of amorphous solid dispersions (ASD). Here, niclosamide-polymer solutions were levitated in a multi-emitter single-axis acoustic levitator and analyzed for 10 min at a High-resolution synchrotron X-ray powder diffraction beamline. This assembly enabled high-quality and fast time-resolved measurements with microliter sample size and measurement of solvent evaporation and recrystallization of niclosamide (NCL). Polymers HPMCP-55S, HPMCP-50, HPMCP-55, Klucel®, and poloxamers were not able to form amorphous dispersions with NCL. Plasdone® and Soluplus® demonstrated excellent properties to form NCL amorphous dispersions, with the last showing superior solubility enhancement. Furthermore, this fast levitation polymer screening showed good agreement with results obtained by conventional solvent evaporation screening evaluated for five days in a stability study, carried out at 40 °C/75% RH. The study showed that acoustic levitation and high-resolution synchrotron combination opens up a new horizon with great potential for accelerating ASD formulation screening and analysis.

Linear Structural Trends and Multi-Phase Intergrowths in Helvine-Group Minerals, (Zn,Fe,Mn)8[Be6Si6O24]S2

Synchrotron high-resolution powder X-ray diffraction (HRPXRD) and Rietveld structure refinements were used to examine the crystal structure of single phases and intergrowths (either two or three phases) in 13 samples of the helvine-group minerals, (Zn,Fe,Mn)8[Be6Si6O24]S2. The helvine structure was refined in the cubic space group P4¯3n. For the intergrowths, simultaneous refinements were carried out for each phase. The structural parameters for each phase in an intergrowth are only slightly different from each other. Each phase in an intergrowth has well-defined unit-cell and structural parameters that are significantly different from the three endmembers and these do not represent exsolution or immiscibility gaps in the ternary solid-solution series. The reason for the intergrowths in the helvine-group minerals is not clear considering the similar radii, identical charge, and diffusion among the interstitial M cations (Zn2+, Fe2+, and Mn2+) that are characteristic of elongated tetrahedral coordination. The difference between the radii of Zn2+ and Mn2+ cations is 10%. Depending on the availability of the M cations, intergrowths may occur as the temperature, pressure, fugacity fS2, and fluid composition change on crystallization. The Be–Si atoms are fully ordered. The Be–O and Si–O distances are nearly constant. Several structural parameters (Be–O–Si bridging angle, M–O, M–S, average <M–O/S>[4] distances, and TO4 rotational angles) vary linearly with the a unit-cell parameter across the series because of the size of the M cation.

Effect of thermal profile on a shift in phase transition temperature of Sb-doped KNN piezoceramic

This work investigated the impact of the thermal profile in the shift of phase transition temperature for KNNS piezoceramic, using high-resolution synchrotron x-ray powder diffraction (SXPD) and dielectric measurement. The temperature-dependent dielectric permittivity and SXPD profile showed that all phase transformations occurred at higher temperature under heating than under cooling. Moreover, under cooling from 227 °C to −163 °C and reheating to 227 °C, none of the unit-cell volumes fully recovered to their initial size. These results suggest that the change in unit-cell volume under heating/cooling plays a significant role in the shift of phase transition temperatures that was observed.

Structural strain and competition between charge density wave and superconductivity in La(Fe,Mn)As(O0.89F0.11) compounds

Selected members of the $\mathrm{La}(\mathrm{Fe},\mathrm{Mn})\mathrm{As}({\mathrm{O}}_{0.89}{\mathrm{F}}_{0.11})$ system were analyzed using high-resolution synchrotron x-ray powder diffraction. The tetragonal to orthorhombic structural transition is progressively recovered in the optimally electron-doped $\mathrm{LaFeAs}({\mathrm{O}}_{0.89}{\mathrm{F}}_{0.11})$ phase by very light Mn substitution; at the same time, superconductivity is suppressed whereas magnetic ordering is restored. Distinct incommensurate satellite peaks develop within different thermal ranges and mark the occurrence of charge density waves characterized by distinct propagation wave vectors, as well as multiple incommensurate structural transitions; in particular, some of them arise in conjunction with the structural transformation process, disappearing after the completion of the dissymmetrization. The thermal evolution of satellite reflections observed at $\mathbf{Q}\ensuremath{\sim}1.93\phantom{\rule{0.16em}{0ex}}{\AA{}}^{--1}$ indicates a strong competition between the charge density waves and the superconductive state. A phase diagram of the $\mathrm{La}(\mathrm{Fe},\mathrm{Mn})\mathrm{As}({\mathrm{O}}_{0.89}{\mathrm{F}}_{0.11})$ system is drawn on the basis of the structural, magnetic, and electronic properties of the analyzed samples.

Simultaneous quantitative recognition of all purines including N6-methyladenine via the host-guest interactions on a Mn-MOF

Simultaneous quantitative recognition of all purines including N6-methyladenine via the host-guest interactions on a Mn-MOF

650 nm-driven syngas evolution from photocatalytic CO2 reduction over Co-containing ternary layered double hydroxide nanosheets

The conversion of solar energy to chemical fuels by CO2 photoreduction reaction (CO2PR) is a promising pathway to alleviate rapid energy consumption crisis. Nevertheless, only a few systems have been reported so far by applying solar energy in visible light region in particular high wavelength (such as λ ≥ 650 nm). Herein, we report an efficient 650 nm-induced CO2 photocatalytic reduction system to syngas by introducing Co into MgAl-layered double hydroxide (CoMgAl-LDH) nanosheets in conjunction with Ru(bpy)3]Cl2·6H2O as photosensitizer, in which [Ru(bpy)3]Cl2·6H2O could be activated to generate photogenerated electrons which further transfer to surface of CoMgAl-LDH for CO2 reduction. Under irradiation >400 nm, the CoMgAl-LDH nanosheets showed excellent CO2 conversion with TOF of 11.57 h−1, 3 times higher than that of CoAl-LDH. Most importantly, up to monochromatic irradiation wavelength at 650 nm, the CoMgAl-LDH nanosheets still displayed optimized syngas evolution rate, with CO rate of 0.35 μmol·h−1 with quantum yield of 0.86%. Furthermore, as evidenced by X-ray absorption fine structure spectroscopy and high-resolution synchrotron X-ray powder diffraction, the proper introduction of Co promoted its dispersion on the laminate of LDH. The suitable dispersion of Co active sites into LDH nanosheets facilitates the transportation of photo-generated electrons to further promote catalytic activity for reaction. This work paves a potential way for CO2PR to syngas under wavelength irradiation up to 650 nm.

A Possible Radiation-Induced Transition from Monazite-(Ce) to Xenotime-(Y)

This study examines two pegmatitic monazite samples (2a and 4b, these numbers are related to a previous study) to determine their crystal chemistry and effects of internal radiation damage using synchrotron high-resolution powder X-ray diffraction and electron-probe micro-analysis. Both the huttonite and cheralite substitutions are discussed. Rietveld structure refinement of sample 2a shows three different phases [2a = monazite-(Ce), 2b = monazite-(Ce), and 2c = xenotime-(Y)] with distinct structural parameters. The changes among the unit-cell parameters between the two monazite-(Ce) phases is more pronounced in the a followed by the b and c unit-cell parameters. Sample 4a is a single-phase monazite-(Sm) that contains 0.164 apfu Th. Phase 2c with space group I41/amd arises from redistribution of La, Ce, Pr, Nd, Sm, Gd, Dy, Si, and Y atoms from those in monazite (space group P21/n). A possible cause for the phase transition from monazite-(Ce) to xenotime-(Y) is α-radiation events over a long geological time. However, other chemical processes cannot be ruled out as a cause for the transition.

Synthesis and structural analysis of nonstoichiometric ternary fulleride K 1.5 Ba 0.25 CsC 60.

The existence of cation-vacancy sites in fullerides might lead to long-range ordering and generate a new vacancy-ordered superstructure. The purpose of this work is to search whether or not long-range ordering of vacant tetrahedral sites, namely superstructure emerges in nonstoichiometric K 1.5 Ba 0.25 CsC 60 fulleride. Therefore, K 1.5 Ba 0.25 CsC 60 with cation-vacancy sites is synthesized using a precursor method to avoid inadequate stoichiometry control and formation of impurity phases within the target composition. For this purpose, first, phase-pure K 6 C 60 , Ba 6 C 60 and Cs 6 C 60 precursors are synthesized. Stoichiometric quantities of these precursors are used for further reaction with C 60 to afford K 1.5 Ba 0.25 CsC 60 . Rietveld analysis of the high-resolution synchrotron X-ray powder diffraction data of the precursors and K 1.5 Ba 0.25 CsC 60 confirms that K 6 C 60 , Ba 6 C 60 and Cs 6 C 60 are single-phase and they crystallize in a body-centered-cubic structure ( Im 3) as reported in the literature. The analysis also shows that K 1.5 Ba 0.25 CsC 60 phase can be perfectly modeled using a face-centered cubic structure. No new peaks appear which could have implied the appearance of a superstructure. This suggests that there is no long-range ordered arrangement of vacant tetrahedral sites in K 1.5 Ba 0.25 CsC 60 .

Structural and physical properties of trilayer nickelates R4Ni3O10 ( R=La , Pr, and Nd)

We investigate the low temperature structural and physical properties of the trilayer nickelates R4Ni3O10 (R = La, Pr and Nd) using resistivity, thermopower, thermal conductivity, specific heat, high-resolution synchrotron powder X-ray diffraction and thermal expansion experiments. We show that all three compounds crystallize with a monoclinic symmetry, and undergo a metal-to-metal (MMT) transition at 135 K (La), 156 K (Pr) and 160 K (Nd). At MMT, the lattice parameters show distinct anomalies; however, without any lowering of the lattice symmetry. Unambiguous signatures of MMT are also seen in magnetic and thermal measurements, which suggest a strong coupling between the electronic, magnetic and structural degrees of freedom in these nickelates. Analysis of thermal expansion yields hydrostatic pressure dependence of MMT in close agreement with experiments. We show that the 9-fold coordinated Pr ions in the rocksalt (RS) layers have a crystal field (CF) split doublet ground state with possible antiferromagnetic ordering at 5 K. The Pr ions located in the perovskite block (PB) layers with 12-fold coordination, however, exhibit a non-magnetic singlet ground state. The CF ground state of Nd in both RS and PB layers is a Kramers doublet. Heat capacity of R = Nd shows a Schottky-like anomaly near35 K, and an upturn below T = 10 K suggesting the presence of short-range correlations between the Nd moments. However, no signs of long-range ordering could be found down to 2 K despite a sizeable theta_p ~ -40 K. The strongly suppressed magnetic long-range ordering in both R = Pr and Nd suggests the presence of strong magnetic frustration in these compounds. The low-temperature resistivity shows a T^0.5 dependence. No evidence for the heavy fermion behavior could be found in any of the three compounds.

Acidic Monosaccharides become Incorporated into Calcite Single Crystals*.

Carbohydrates, along with proteins and peptides, are known to represent a major class of biomacromolecules involved in calcium carbonate biomineralization. However, in spite of multiple physical and biochemical characterizations, the explicit role of saccharide macromolecules (long chains of carbohydrate molecules) in mineral deposition is not yet understood. In this study, we investigated the influence of two common acidic monosaccharides (MSs), the two simplest forms of acidic carbohydrates, namely glucuronic and galacturonic acids, on the formation of calcite crystals in vitro. We show here that the size, morphology, and microstructure of calcite crystals are altered when they are grown in the presence of these MSs. More importantly, these MSs were found to become incorporated into the calcite crystalline lattice and induce anisotropic lattice distortions, a phenomenon widely studied for other biomolecules related to CaCO3 biomineralization, but never before reported in the case of single MSs. Changes in the calcite lattice induced by MSs incorporation were precisely determined by high-resolution synchrotron powder X-ray diffraction. We believe that the results of this research may deepen our understanding of the interaction of saccharide polymers with an inorganic host and shed light on the implications of carbohydrates for biomineralization processes.