High-resolution Synchrotron X-ray Diffraction Research Articles

Direct observation of lattice symmetry breaking at the hidden-order transition in URu2Si2.

Since the 1985 discovery of the phase transition at THO=17.5 K in the heavy-fermion metal URu2Si2, neither symmetry change in the crystal structure nor large magnetic moment that can account for the entropy change has been observed, which makes this hidden order enigmatic. Recent high-field experiments have suggested electronic nematicity that breaks fourfold rotational symmetry, but direct evidence has been lacking for its ground state in the absence of magnetic field. Here we report on the observation of lattice symmetry breaking from the fourfold tetragonal to twofold orthorhombic structure by high-resolution synchrotron X-ray diffraction measurements at zero field, which pins down the space symmetry of the order. Small orthorhombic symmetry-breaking distortion sets in at THO with a jump, uncovering the weakly first-order nature of the hidden-order transition. This distortion is observed only in ultrapure samples, implying a highly unusual coupling nature between the electronic nematicity and underlying lattice.

Effect of Cooling Rates on Phase Separation in 0.5Li2MnO3·0.5LiCoO2 Electrode Materials for Li-Ion Batteries

The results of a detailed structural investigation on the influence of cooling rates in the synthesis of lithium- and manganese-rich 0.5Li2MnO3·0.5LiCoO2 composite electrode materials, which are of interest for Li-ion battery applications, are presented. It is shown that a low-temperature, intermediate firing step, often employed in cathode synthesis, yields a minor secondary component representing a polydisperse distribution of lattice parameters, not found in the absence of low-temperature treatments. However, regardless of the heating and cooling conditions employed, all samples present two distinctly different local environments as evidenced by X-ray absorption fine structure spectroscopy (XAFS) and nuclear magnetic resonance (NMR) analysis. Transmission electron microscopy (TEM) data show discrete domain structures that are consistent with the XAFS and NMR findings. Furthermore, high resolution synchrotron X-ray diffraction (HR-XRD), as well as the XAFS and NMR data show no discernible differences be...

Flexible Structure of a Thermally Stable Hybrid Aluminosilicate Built with Only the Three-Ring Unit

Organic–inorganic aluminosilicate hybrids are an attractive new class of materials that add organic functionalities to conventional properties of solid inorganic catalysts. ECS-17, a novel crystalline hybrid, was synthesized using 1,4-bis-(triethoxysilyl)-benzene as the sole silicon source. Its structure was solved by direct methods starting from high-resolution synchrotron X-ray diffraction data and is composed of inorganic layers, characterized by 10 rings, held together by phenylene rings. ECS-17 is the first aluminosilicate built from only the three-ring secondary building unit. This new material shows intriguing reversible collapsibility upon dehydration/rehydration. Mild thermal treatment under vacuum causes its crystalline structure to collapse due to facile elimination of the water molecules around the cations. Successive exposure to ambient atmospheric moisture gives back the hydrated crystalline form. ECS-17 shows remarkably high thermal stability for a hybrid, being stable up to 450 °C under va...

Structure and ferroelectricity of nonstoichiometric (Na0.5Bi0.5)TiO3

Stoichiometric (Na0.5Bi0.5)TiO3 (NBT) adopts the ABO3 perovskite structure with the A-site equally occupied by Na+ and Bi3+ ions. However, non-stoichiometric compositions can be synthesized intentionally or unintentionally. To determine the effect of A-site nonstoichiometry on the crystal structure and ferroelectricity of NBT, the composition of (Na0.5−xBi0.5+x)TiO3+x was varied using x = −0.01, −0.005, 0, 0.005, and 0.01. High resolution synchrotron x-ray diffraction and Rietveld refinement revealed that a shift in either direction from x = 0 results in a decrease in the spontaneous ferroelastic strain. Ferroelectric hysteresis and piezoelectric coefficients were found to be optimum in the stoichiometric composition.

Large strains accompanying field-induced ergodic phase-polar ordered phase transformations in Bi(Mg0.5Ti0.5)O3–PbTiO3–(Bi0.5Na0.5)TiO3 ternary system

A composition-induced pseudocubic–tetragonal structural transition was found to be accompanied by a relaxor phase transformation in xBi(Mg0.5Ti0.5)O3–(0.75 − x)PbTiO3–0.25(Bi0.5Na0.5)TiO3 ternary solid solutions. Dielectric and ferroelectric measurements suggest the coexistence of ergodic and nonergodic relaxor phases within a single pseudocubic phase zone for samples with 0.50 < x < 0.51 where large electromechanical strains of up to 0.43% (Smax/Emax = 621 pm/V) can be generated. The mechanism was mainly ascribed to the accumulated effects of field-modulated continuous and reversible transformations from a pseudocubic ergodic phase to a rhombohedral short-range ordered phase (but not nonergodic polar phase), and finally to a long-range ordered ferroelectric tetragonal phase. These procedures were found to be strongly dependent on the applied field magnitudes. These findings were reasonably approved by a couple of measurements such as dielectric–temperature–frequency spectrum, ferroelectric polarization/strain hysteresis loops, polarization current density curves and particularly ex situ Raman spectrum and in situ high-resolution synchrotron X-ray diffraction.

Effect of Mo6+ doping on electrochemical performance of anatase TiO2 as a high performance anode material for secondary lithium-ion batteries

The effects of molybdenum (Mo6+) doping on the electrochemical properties of anatase-type titanium dioxide (TiO2) were investigated. The Mo6+-doped TiO2 samples were prepared using a simple and cost-effective solvothermal method with the doping levels of 1, 3, and 5wt%, followed by annealing at a low temperature of 300°C for 5h. High-resolution synchrotron X-ray diffraction and electron microscopy were conducted to know the structural and morphological properties of doped TiO2 samples. The dopant significantly suppresses the growth of TiO2 grains and reduces the particles sizes, which can also improve markedly the performance and stability of charge/discharge cycles. The particles sizes are in the range of 115–250nm and 5–10nm for undoped and Mo-doped TiO2 nanoparticle samples, respectively. Electrochemical results show that the Mo6+-doped TiO2 nanoparticle samples display a significantly lower charge transfer resistance, higher rate capability and excellent reversibility. Author’s believed that the high rate performance offered by Mo-doped TiO2 nanoparticle electrodes may be attributed to the enhanced electronic and ionic conductivity, which are achieved by increasing the number of Ti4+ vacancies in the lattice via Mo6+ doping, which may lead to the generation of more free holes in the doped p-type semiconductor. The increased hole concentration in the valence band can contribute to the electrical conductivity of the doped sample.

The power ofin situpulsed laser deposition synchrotron characterization for the detection of domain formation during growth of Ba0.5Sr0.5TiO3on MgO

A highly sophisticated pulsed laser deposition (PLD) chamber has recently been installed at the NANO beamline at the synchrotron facility ANKA (Karlsruhe, Germany), which allows for comprehensive studies on the PLD growth process of dielectric, ferroelectric and ferromagnetic thin films in epitaxial oxide heterostructures or even multilayer systems by combining in situ reflective high-energy diffraction with the in situ synchrotron high-resolution X-ray diffraction and surface diffraction methods. The modularity of the in situ PLD chamber offers the opportunity to explore the microstructure of the grown thin films as a function of the substrate temperature, gas pressure, laser fluence and target-substrate separation distance. Ba0.5Sr0.5TiO3 grown on MgO represents the first system that is grown in this in situ PLD chamber and studied by in situ X-ray reflectivity, in situ two-dimensional reciprocal space mapping of symmetric X-ray diffraction and acquisition of time-resolved diffraction profiles during the ablation process. In situ PLD synchrotron investigation has revealed the occurrence of structural distortion as well as domain formation and misfit dislocation which all depend strongly on the film thickness. The microstructure transformation has been accurately detected with a time resolution of 1 s. The acquisition of two-dimensional reciprocal space maps during the PLD growth has the advantage of simultaneously monitoring the changes of the crystalline structure as well as the formation of defects. The stability of the morphology during the PLD growth is demonstrated to be remarkably affected by the film thickness. A critical thickness for the domain formation in Ba0.5Sr0.5TiO3 grown on MgO could be determined from the acquisition of time-resolved diffraction profiles during the PLD growth. A splitting of the diffraction peak into two distinguishable peaks has revealed a morphology change due to modification of the internal strain during growth.

Nature of low compressibility and anisotropic elasticity in YbB2

Recent high-resolution synchrotron X-ray diffraction experiments (Kalkan et al., 2012) investigated bulk modulus and compressibility of high purity YbB2 and found that its compressibility can be compared even to that of diamond. In this paper we investigate the structural, compressibility and electronic properties of rare-earth YbB2 using density functional theory to illuminate the nature of its low compressibility and anisotropic elasticity. The calculated results are in agreement with the available theoretical and experimental data and confirm YbB2 as a hard material. The nature of YbB2 hardness and low compressibility is revealed by analyses of its electronic and directional bonding properties: it lies in very strong in-layer and strong enough between-layer bonds. The isotropic bulk modulus, shear modulus, Young’s modulus, elastic anisotropy, wave velocities and Debye temperature of YbB2, under ambient and pressures up to 300GPa are also discussed. Pressure induces expected behavior in most of these properties (monotonic increase), except in elastic constant c44, which softens and could lead to elastic instability. Furthermore, anisotropic factors, which are very different at zero pressure, give similar values at the pressure of 300GPa, closing the gap between compressional and shear anisotropy. Ductility unexpectedly increases with pressure.

Nondestructive Monitoring of Defect Evolution in Epitaxial CdTe Thin Layers Grown on Si(111)

Reduction of crystalline defect density and size is a major issue in optimization of thin film for industrial scale applications. It is particularly hard to achieve defect minimization due to the lack of statistically relevant techniques where defect-induced strain information is also available. In this work, we use a combination of high-resolution transmission electron microscopy and synchrotron X-ray diffraction to investigate the evolution of defects during the growth of highly mismatched cadmium telluride (CdTe) films on silicon(111) as a function of growth temperature and layer thickness. High-resolution transmission electron microscopy was employed to show that the grown layers are epitaxial, following the [111] substrate orientation, and to identify the main defect type (double twins). Detailed reciprocal space maps obtained by synchrotron X-ray diffraction were used to identify the presence of additional intensities near the (113) and (002) CdTe bulk reciprocal space positions caused by these defe...

Heteroepitaxial growth of multidomain Ga2O3/sapphire(001) thin films deposited using radio frequency magnetron sputtering

We investigated heteroepitaxial growth of multidomain Ga2O3 thin films deposited using radio frequency magnetron sputtering onto sapphire(001) substrates. The crystalline orientation of the films was examined using high-resolution synchrotron X-ray diffraction. Corundum α- and monoclinic β-Ga2O3 coexisted in the as-grown samples. Azimuthal angle scans of the in-plane β(020) and α(303̄0) Bragg peaks revealed that the α-Ga2O3 and β-Ga2O3 both showed 12-fold in-plane rotational symmetry and, in particular, that the α-Ga2O3 domains rotated 30° to the in-plane direction were tilted ±3° to the sapphire[112̄0] direction. The optical bandgaps of the as-grown and annealed samples were estimated using ultraviolet–visible–infrared spectroscopy.

Polar nanoregions and dielectric properties in high-strain lead-free 0.93(Bi1/2Na1/2)TiO3-0.07BaTiO3 piezoelectric single crystals

A structural coexistence of rhombohedral (R) and tetragonal (T) phases has been revealed in the (001)c-cut lead-free 0.93(Bi1/2Na1/2)TiO3–0.07BaTiO3 (BNB7T) piezoelectric crystals, which grown by the self-flux method, in the lower temperatures by high-resolution synchrotron X-ray diffraction, reciprocal space mapping, and transmission electron microscopy. The dielectric permittivity exhibits a thermal hysteresis in the region of 120–260 °C, implying a first-order-like phase transition from R+T to T. The real part (ε′) of dielectric permittivity begins to deviates from the Curie-Weiss equation, ε′ = C/(T − To), from the Burns temperature TB = 460 °C, below which the polar nanoregions (or nanoclusters) develop and attenuate dielectric responses. The polar nanoregions of 5–10 nm were revealed by high-resolution transmission electron microscope. The normal piezoelectric coefficient d33 exhibits a rapid increase at E = 15–20 kV/cm and reaches a maximum of d33 ∼450 pC/N. The high piezoelectric response and E-field induced strain in BNB7T single crystals can be attributed to structural phase transitions under an E-field application.

Low Temperature Preparation and Electrochemical Properties of LiFeSi2O6

The growing demand for Li-ion batteries requires the development of inexpensive materials that can be made in a sustainable fashion. Here we report a new low-temperature preparation for and the first electrochemical characterization of LiFeSi2O6, a hugely Earth-abundant, rock-forming mineral. We have found that LiFeSi2O6 undergoes a reversible electrochemical reaction against Li centered around 2 V with capacities near 60% of the theoretical maximum. We employ high resolution synchrotron X-ray and neutron diffraction to characterize the structure and correlate the rigid connectivity of the framework with the very slow kinetics of diffusion.

Control of oxygen octahedral rotations and physical properties inSrRuO3films

Control of octahedral rotations in the ABO${}_{3}$ perovskite oxides has been of great interest due to its potential in rationally discovering and designing new multifunctional phases. In this study, we show that octahedral rotations of the SrRuO${}_{3}$ films can be controlled by oxygen vacancies as well as by interfacial coupling, which further determines the physical properties. Half-integer reflections using high-resolution synchrotron x-ray diffraction were carried out to determine the octahedral rotation pattern of SrRuO${}_{3}$ films on SrTiO${}_{3}$ substrates. The transition of RuO${}_{6}$ rotation pattern accompanied by the structural change from monoclinic $P$2${}_{1}/m$ to tetragonal $F$4/mmc can be understood from the preference of oxygen vacancies in the SrO atomic plane and the coupling of octahedra across the interface between film and substrate. The field angle dependence of magnetoresistance further confirmed the structural phase transition with changes in octahedral rotations. The monoclinic phase has the uniaxial magnetic easy axis 30\ifmmode^\circ\else\textdegree\fi{} away from the [001] direction towards the [010] direction while the tetragonal phase has uniaxial magnetic easy axis along the fourfold axis which is perpendicular to the film surface. This study demonstrates the ability to control the octahedral rotations in perovskite films and its importance when designing thin films and multilayers with desired functional property.

A-Type Antiferro-Orbital Ordering withI41/aSymmetry and Geometrical Frustration in the Spinel VanadateMgV2O4

We conduct a detailed structural analysis of the S=1 pyrochlore antiferromagnet MgV2O4, which exhibits an antiferromagnetic ordering marginally at TN=40 K, triggered by a structural transition from cubic to tetragonal symmetry at TS=62 K, using high resolution synchrotron x-ray diffraction and convergent beam electron diffraction. We reveal that the tetragonal phase below TS has the symmetry of I4(1)/a and that the distortion pattern of VO6 octahedra is consistent with A-type antiferro-orbital ordering with alternating stacking of layers with yz/xy orbital chains and zx/xy orbital chains along the tetragonal c axis. This implies that an anisotropic coupling of V moments produced by the orbital ordering below TS primarily brings about the antiferromagnetic ordering.

Electrochemical Na Extraction/Insertion of Na3V2O2x(PO4)2F3–2x

A mixed-valence V3+/V4+ composite material belonging to the Na3V2O2x(PO4)2F3–2x/C family is synthesized and the electrochemical Na extraction/insertion mechanism is determined using a combination of high-resolution synchrotron X-ray diffraction (XRD) data, X-ray absorption spectroscopy (XAS), 23Na and 19F solid state nuclear magnetic resonance (NMR), double titration (for the elucidation of the vanadium oxidation state), and electrochemical measurements. The vanadium oxidation state is found to be +3.8 for the as-prepared sample. Detailed analysis of the cathode structural evolution illustrated that the V4+/V5+ couple is active in this compound during electrochemical cycling between 2.8 V and 4.3 V. This study demonstrates how the sodium-ion extraction and insertion pathways in cathode materials can be followed (and verified) using several experimental techniques, especially when multiple potential oxidation states are present in the parent compound.

Evidence for a tricritical point coinciding with the triple point in (Pb0.94Sr0.06)(ZrxTi1−x)O3: A combined synchrotron x-ray diffraction, dielectric, and Landau theory study

We present here results of high resolution synchrotron x-ray diffraction (SXRD) and dielectric studies in conjunction with Landau theory considerations on (Pb0.94Sr0.06)(ZrxTi1-x)O3 compositions in the vicinity of the morphotropic phase boundary (MPB) to find evidence for the flattening of the free energy surface at the MPB proposed in recent ab-initio studies on strongly piezoelectric ceramics. SXRD results reveal that the tetragonal and pseudorhombohedral monoclinic compositions with x=0.515 and 0.550 transform directly into the cubic paraelectric phase, whereas for 0.520<x<0.545, the pseudotetragonal as well as pseudorhombohedral monoclinic compositions first transform to the tetragonal phase and then to the cubic phase. Our results reveal the existence of a triple point at x~0.550. It is shown that the tetragonal to cubic transition, irrespective of the composition, upto x~0.545 is accompanied with a discontinuous change in the unit cell volume and thermal hysteresis confirming first order nature of this transition. The pseudorhombohedral monoclinic composition for x=0.550, on the other hand, transforms directly into the cubic phase in a second order manner. Our experimental results thus reveal a crossover from first order to second order phase transition through a tricritical point around x=0.550. Landau theory calculations also confirm gradual flattening of the free energy surface on approaching the tricritical composition x=0.550. We conclude that the triple point in the PZT phase diagram is indeed a tricritical point.

Complex 5d Magnetism in a Novel S = 1/2 Trimer System, the 12L Hexagonal Perovskite Ba4BiIr3O12

The 12L hexagonal perovskite Ba4BiIr3O12 has been synthesized for the first time and characterized using high-resolution neutron and synchrotron X-ray diffraction as well as physical properties measurements. The structure contains Ir3O12 linear face-sharing octahedral trimer units, bridged by corner-sharing BiO6 octahedra. The average electronic configurations of Ir and Bi are shown to be +4(d(5)) and +4(s(1)), respectively, the same as for the S = 1/2 dimer system Ba3BiIr2O9, which undergoes a spin-gap opening with a strong magnetoelastic effect at T* = 74 K. Anomalies in magnetic susceptibility, heat capacity, electrical resistivity, and unit cell parameters indeed reveal an analogous effect at T* ≈ 215 K in Ba4BiIr3O12. However, the transition is not accompanied by the opening of a gap in spin excitation spectrum, because antiferromagnetic coupling among S = 1/2 Ir(4+) (d(5)) cations leads to the formation of a S = 1/2 doublet within the trimers, vs S = 0 singlets within dimers. The change in magnetic state of the trimers at T* leads to a structural distortion, the energy of which is overcompensated for by the formation of S = 1/2 doublets. Extending this insight to the dimer system Ba3BiIr2O9 sheds new light on the more pronounced low-temperature anomalies observed for that compound.

Characterization of Novel Lithium Battery Cathode Materials by Spectroscopic Methods: The Li5+xFeO4 System

The novel, lithium-rich oxide-phase Li₅FeO₄ (LFO) could, in theory, deliver a specific capacity >900 mAh/g when deployed as a cathode or cathode precursor in a battery with a lithium-based anode. However, research results to date on LFO indicate that less than one of the five Li⁺ cations can be reversibly de-intercalated/re-intercalated during repetitive charging and discharging cycles. In the present research, the system Li5+xFeO₄ with x values in the range of 0.0-2.0 was investigated by a combination of Raman and X-ray absorption spectroscopic methods supported by X-ray diffraction (XRD) analysis in order to determine if the Li₅FeO₄ lattice would accommodate additional Li⁺ ions, with concomitant lowering of the valence on the FeIII cations. Both the Raman phonon spectra and the XRD patterns were invariant for all values of x, strongly indicating that additional Li⁺ did not enter the Li₅FeO₄ lattice. Also, Raman spectral results and high-resolution synchrotron XRD data revealed the presence of second-phase Li₂O in all samples with x greater than 0.0. Synchrotron X-ray absorption spectroscopy at the Fe kα edge performed on the sample with a Li-Fe ratio of 7.0 (i.e., x = 2.0) showed no evidence for the presence of FeII. This resistance to accepting more lithium into the Li₅FeO₄ structure is attributed to the exceedingly stable nature of high-spin FeIII in tetrahedral "FeIIIO₄" structural units of Li₅FeO₄. Partial substitution of the FeIII with other cations could provide a path toward increasing the reversible Li⁺ content of Li5xFeO₄-type phases.

Spatially‐Resolved In‐Situ Structural Study of Organic Electronic Devices with Nanoscale Resolution: The Plasmonic Photovoltaic Case Study

A novel high spatial resolution synchrotron X-ray diffraction stratigraphy technique has been applied in-situ to an integrated plasmonic nanoparticle-based organic photovoltaic device. This original approach allows for the disclosure of structure-property relations linking large scale organic devices to length scales of local nano/hetero structures and interfaces between the different components.

Conducting linear chains of sulphur inside carbon nanotubes

Despite extensive research for more than 200 years, the experimental isolation of monatomic sulphur chains, which are believed to exhibit a conducting character, has eluded scientists. Here we report the synthesis of a previously unobserved composite material of elemental sulphur, consisting of monatomic chains stabilized in the constraining volume of a carbon nanotube. This one-dimensional phase is confirmed by high-resolution transmission electron microscopy and synchrotron X-ray diffraction. Interestingly, these one-dimensional sulphur chains exhibit long domain sizes of up to 160 nm and high thermal stability (~800 K). Synchrotron X-ray diffraction shows a sharp structural transition of the one-dimensional sulphur occurring at ~450–650 K. Our observations, and corresponding electronic structure and quantum transport calculations, indicate the conducting character of the one-dimensional sulphur chains under ambient pressure. This is in stark contrast to bulk sulphur that needs ultrahigh pressures exceeding ~90 GPa to become metallic.