High-resolution Synchrotron X-ray Diffraction Research Articles

Charge ordering driven metal-insulator transition in the layered cobaltiteHoBaCo2O5.5

In this Brief Report we report high-resolution synchrotron x-ray diffraction and x-ray pair-distribution-function analysis as a function of temperature on the ${\text{HoBaCo}}_{2}{\text{O}}_{5.5}$ cobaltite. These investigations provided a direct evidence of a structural phase transition from an orthorhombic to a monoclinic phase in the ${\text{HoBaCo}}_{2}{\text{O}}_{5.5}$ layered cobaltite which occurs concomitantly with the metal to insulator transition. The structural data suggest a possible charge ordered state in the monoclinic phase which may be responsible for the insulating character at low temperature.

Design and application of a high-temperature microfurnace for anin situX-ray diffraction study of phase transformation

Thermal treatment of mineral ores such as ilmenite can initiate phase transformations that could affect their activation or deactivation, subsequently influencing their ability to dissolve in a leaching agent. Most laboratory-based X-ray diffraction (XRD) studies were carried out ex situ in which realistic diffraction patterns could not be obtained simultaneously with occurring reactions and were time-consuming. The availability of synchrotron-radiation-based XRD not only allows in situ analysis, but significantly shortens the data recording time. The present study details the design of a robust high-temperature microfurnace which allows thermal processing of mineral ore samples and the simultaneous collection of high-resolution synchrotron XRD data. In addition, the application of the manufactured microfurnace for in situ study of phase transformations of ilmenite ore under reducing conditions is demonstrated.

In situ observation of phase transformation in Fe–0.15C binary alloy

Time-resolved high resolution synchrotron X-ray diffraction has been used to conduct in situ studies of the temporal evolution of α → γ and γ → α transformations. Moreover, high temperature laser scanning confocal microscopy with an infrared imaging furnace has been used to directly observe the morphological development of γ → α transformations. It makes possible that phase transformation can be identified in real time during heating and continuously cooling process. Phase transformation process of Fe–0.15C binary alloy was analyzed as a combination of these two experimental facilities.

Tetragonal micro/nanotwins in 0.91Pb(Zn1/3Nb2/3)O3−0.09PbTiO3 revealed by reciprocal space mapping

Reciprocal space mapping (RSM) of the relaxor ferroelectric 0.91Pb(Zn1/3Nb2/3)O3−0.09PbTiO3 (PZN-9%PT) single crystals has been performed by using high-resolution synchrotron x-ray diffraction as a function of temperature. The PZN–9%PT crystal consists of tetragonal micro/nanotwin domains and undergoes a sequence of rhombohedral+tetragonal→tetragonal→cubic phase transformation upon heating. The rhombohedral-to-tetragonal temperature occurs at ≅70 °C. The observed RSM patterns can be explained by the micro/nanotwin structures and their corresponding diffraction patterns.

How to Make the Ionic Si−O Bond More Covalent and the Si−O−Si Linkage a Better Acceptor for Hydrogen Bonding

Variation of a bond angle can tune the reactivity of a chemical compound. To exemplify this concept, the nature of the siloxane linkage (Si-O-Si), the most abundant chemical bond in the earth's crust, was examined using theoretical calculations on the molecular model compounds H(3)SiOSiH(3), (H(3)Si)(2)OHOH, and (H(3)Si)(2)OHOSiH(3) and high-resolution synchrotron X-ray diffraction experiments on 5-dimethylhydroxysilyl-1,3-dihydro-1,1,3,3-tetramethyl-2,1,3-benzoxadisilole (1), a molecular compound that gives rise to the formation of very rare intermolecular hydrogen bonds between the silanol groups and the siloxane linkages. For theoretical calculations and experiment, electronic descriptors were derived from a topological analysis of the electron density (ED) distribution and the electron localization function (ELF). The topological analysis of an experimentally obtained ELF is a newly developed methodology. These descriptors reveal that the Si-O bond character and the basicity of the siloxane linkage strongly depend on the Si-O-Si angle. While the ionic bond character is dominant for Si-O bonds, covalent bond contributions become more significant and the basicity increases when the Si-O-Si angle is reduced from linearity to values near the tetrahedral angle. Thus, the existence of the exceptional intermolecular hydrogen bond observed for 1 can be explained by its very small strained Si-O-Si angle that adopts nearly a tetrahedral angle.

High-temperature synchrotron X-ray diffraction study of LaMn 7O 12

The crystal structure of the 1:3 A-site ordered perovskite LaMn 7O 12 with manganese atoms on both the A- and B-sites, was investigated with high-temperature in-situ synchrotron X-ray diffraction (SXRD) from room temperature up to 803 K as well as with high-resolution SXRD at room temperature. A first order structural phase transition from a body centered monoclinic I2/ m to a cubic Im 3 ¯ structure (from a + b + c + to a + a + a + tilt system) occurs around T c = 653 K as evidenced by discontinuous jumps in unit cell dimensions and differential scanning calorimetric data. The temperature dependence of the Mn–O bond distances suggests that the driving force for the transition is relaxation of the Jahn–Teller distortion and subsequent change in the tilting pattern of the MnO 6 octahedra.

A curved image-plate detector system for high-resolution synchrotron X-ray diffraction

The developed curved image plate (CIP) is a one-dimensional detector which simultaneously records high-resolution X-ray diffraction (XRD) patterns over a 38.7 degrees 2theta range. In addition, an on-site reader enables rapid extraction, transfer and storage of X-ray intensity information in </=30 s, and further qualifies this detector to study kinetic processes in materials science. The CIP detector can detect and store X-ray intensity information linearly proportional to the incident photon flux over a dynamical range of about five orders of magnitude. The linearity and uniformity of the CIP detector response is not compromised in the unsaturated regions of the image plate, regardless of saturation in another region. The speed of XRD data acquisition together with excellent resolution afforded by the CIP detector is unique and opens up wide possibilities in materials research accessible through X-ray diffraction. This article presents details of the basic features, operation and performance of the CIP detector along with some examples of applications, including high-temperature XRD.

Crystal structure and phase transitions across the metal-superconductor boundary in theSmFeAsO1−xFx(0≤x≤0.20)family

The fluorine-doped rare-earth iron oxyarsenides ${\text{REFeAsO}}_{1\ensuremath{-}x}{\text{F}}_{x}$ ($\text{RE}=\text{rare}$ earth) have recently emerged as a new family of high-temperature superconductors with transition temperatures $({T}_{c})$ as high as 55 K. Here we use high-resolution synchrotron x-ray diffraction to study the structural properties of ${\text{SmFeAsO}}_{1\ensuremath{-}x}{\text{F}}_{x}$ $(0\ensuremath{\le}x\ensuremath{\le}0.20)$ in which superconductivity emerges near $x\ensuremath{\sim}0.07$ and ${T}_{c}$ increases monotonically with doping up to $x\ensuremath{\sim}0.20$. We find that orthorhombic symmetry survives through the metal-superconductor boundary well into the superconducting regime and the structural distortion is only suppressed at doping levels, $x\ensuremath{\ge}0.15$, when the superconducting phase becomes metrically tetragonal. Remarkably this crystal symmetry crossover coincides with reported drastic anomalies in the resistivity and the Hall coefficient, and a switch of the pressure coefficient of ${T}_{c}$ from positive to negative, thereby implying that the low-temperature structure plays a key role in defining the electronic properties of these superconductors.

Structure of Li2FeSiO4

A large-scale lithium-ion battery is the key technology toward a greener society. A lithium iron silicate system is rapidly attracting much attention as the new important developmental platform of cathode material with abundant elements and possible multielectron reactions. The hitherto unsolved crystal structure of the typical composition Li2FeSiO4 has now been determined using high-resolution synchrotron X-ray diffraction and electron diffraction experiments. The structure has a 2 times larger superlattice compared to the previous beta-Li3PO4-based model, and its origin is the periodic modulation of coordination tetrahedra.

Structural phase transformations and nanotwin domains in0.93Pb(Zn1/3Nb2/3)O3–0.07PbTiO3

By means of combined dielectric permittivity and thermal current density measurements andin situ high-resolution synchrotron x-ray diffraction study, it is shown that the unpoled and poled0.93Pb(Zn1/3Nb2/3)O3–0.07PbTiO3 (PZN–7%PT) singlecrystals undergo a R−(R+RNT+T+TNT)−(T+TNT)−C transformation sequence upon zero-field heating, whereR,T and C are rhombohedral, tetragonal and cubic phases, respectively. Rhombohedral(RNT) andtetragonal (TNT) nanotwin domains were detected in the vicinity of theR–T transformationtemperature (TR−T) in both the unpoled and poled states. These nanotwins are likely bridging phases whichhelp to alleviate the internal stresses accompanying the phase transformations.

Magnetoelastic effects in BiMn2O5: a high-resolution synchrotron X-ray diffraction study

Magnetoelastic effects in BiMn₂O₅: a high-resolution synchrotron X-ray diffraction study

Investigation on the hydrated and dehydrated forms of the ion-exchanged microporous stannosilicate EMS-2

The ion-exchange properties and characterization of EMS-2, a new stannosilicate isostructural with the natural zirconosilicate lemoynite, are reported. EMS-2 samples were characterized by high resolution synchrotron X-ray diffraction, elemental, thermogravimetric and differential scanning calorimetry analyses. The crystal structure of Mg, Ca, Sr and Ba exchanged samples was refined revealing the positions and occupancies of the extraframework cations and water molecules. After dehydration, the crystal structure of ion-exchanged EMS-2 was investigated by in-situ high temperature X-ray powder diffraction. The experiments indicated that the materials are stable at least up to 400 °C. Mg- and Ca-EMS-2 possess a very rigid structure and only slight variations of the unit cell parameters were noted after dehydration. At a difference, at high temperature Sr- and Ba-exchanged samples undergo a phase transition. The new structures were determined and the phase transition was rationalized as an extensive reorganization of cations after loosing the coordinated water molecules. This process is possibly driven by the need to attain a coordination environment as favourable as possible. This produces a strong framework distortion, associated to a structure contraction in the b direction, which drives to doubling the c cell parameter.

COMBINED NORMAL AND HIGH-RESOLUTION SYNCHROTRON X-RAY DIFFRACTION STUDY OF SURFACE LAYER PZN-4.5%PT FERROELECTRIC SINGLE CRYSTAL

An extremely broad lower 2θ peak adjacent to the major (002) rhombohedral peak has been frequently observed in standard XRD profiles of bulk PZN-PT single crystals at room temperature. To understand the original and nature of this lower 2θ peak, high-resolution synchrotron X-ray diffraction study was carried out. The synchrotron (002) mapping together with a fracturing technique confirmed that the lower 2θ peak arises from a polishing-induced surface layer of "highly stressed rhombohedral state of monoclinic symmetry" which, structurally, may be likened to one full of "incipient monoclinic nuclei" of a range of lattice parameters. These "incipient" monoclinic nuclei/phases are microscopic in dimensions and are placed under intense in-plane compressive stress in the surface layer. All these contribute to the extreme broadness of the lower 2θ peak. The present work shows that deformation of relaxor single crystals occurs readily by stress-induced phase transformation of the material from the rhombohedral state to other lower symmetry states. The lower 2θ peak, and hence the "incipient" monoclinic surface layer, is fairly resistant to annealing and low-field poling but can be largely eliminated when the as-polished sample was poled to sufficiently high field (i.e., 1.5 kV/mm) at room temperature. After annealing, however, the "incipient" monoclinic surface layer became more resistant to poling such that remnant of the lower 2θ peak persisted even after high-field poling.

Phase transformations in annealed PZN-4.5%PT single crystals

Phase transformations of annealed bulk 0.955Pb(Zn1/3Nb2/3)O3–0.045PbTiO3 (PZN-4.5%PT) single crystals have been examined by means of dielectric permittivity, thermal current, domain structure, and high-resolution synchrotron x-ray diffraction as a function of temperature. The result shows that annealed (unpoled) bulk PZN-4.5%PT single crystal undergoes an R-T-C transformation sequence upon zero-field heating, where R, T, and C are the rhombohedral, tetragonal, and cubic phases, respectively. Diffractions pertaining to rhombohedral and tetragonal nanotwins are detected. These diffractions can easily be mistaken as the monoclinic diffractions, which, however, are not supported by our thermal current measurement. The nanotwin structure plays an important role in bridging the R-T and T-C transformations, possibly by alleviating the accompanying transformation stresses.

Short- and Long-Range Orbital Order in Phase Separated Pr0.50Ca0.50Mn0.99Ti0.01O3: Its Role in Thermal Hysteresis

By means of high resolution synchrotron X-ray and neutron powder diffraction we have investigated the structural evolution of Pr 0.50 Ca 0.50 Mn 0.99 Ti 0.01 O 3 . We have found two structural transitions on cooling; the first takes place at T co ≃ 240 K and the second in a wide temperature range around 100-140 K. Below the first transition two phases coexist; one presents robust charge/orbital ordering, characterized by strong lattice distortions and low strain, and the second presents charge/orbital order characterized by smaller lattice distortions with remarkable spatial fluctuations and short ranged orbital ordering. This second phase is metastable giving rise to thermal hysteresis of structural and macroscopic properties in the cooling-heating cycle. We have observed that thermal hysteresis is due to (i) the transformation of a huge region of short-ranged order into long-ranged ordered regions and (ii) a hardening of the remaining short-ranged regions in which the lattice distortion grows and the strain diminishes. We also report a detailed characterization of the low temperature (ground state) coexisting phases including their structural details, ordered magnetic structures, coherence lengths, microstructural details, and so forth. A great degree of magnetic disorder characterizes the low temperature ground state of the investigated highly diluted manganite.

Phase transformation in unpoled bulk Pb(Zn1∕3Nb2∕3)O3–8%PbTiO3 single crystals revealed by the fracturing technique

Polished-and-annealed surfaces of bulk Pb(Zn1∕3Nb2∕3)O3–PbTiO3 (PZN-PT) single crystals were covered with a deformed layer and, hence, were unsuitable for structural study by means of x-ray diffraction technique. In contrast, fractured surfaces of bulk single crystals were relatively strain-free giving rise to distinctive diffraction patterns. Using the fracturing technique and high-resolution synchrotron x-ray diffraction, the present work shows that unpoled (annealed) PZN-8%PT single crystal undergoes a (MC)-T-C transformation upon heating under zero field condition, where T and C are the tetragonal and cubic phases, respectively. The symbol (MC) indicates an “apparent” type-C monoclinic phase, which in fact may be a rhombohedral phase of complicated domain structures.

Magnetoelastic and thermal effects in theBiMn2O5lattice: A high-resolution x-ray diffraction study

High-resolution synchrotron x-ray diffraction measurements were performed on single crystalline and powder samples of $\mathrm{Bi}{\mathrm{Mn}}_{2}{\mathrm{O}}_{5}$. A linear temperature dependence of the unit cell volume was found between ${T}_{N}=38$ and $100\phantom{\rule{0.3em}{0ex}}\mathrm{K}$, suggesting that a low-energy lattice excitation may be responsible for the lattice expansion in this temperature range. Between ${T}^{*}\ensuremath{\sim}65\phantom{\rule{0.3em}{0ex}}\mathrm{K}$ and ${T}_{N}$, all lattice parameters showed incipient magnetoelastic effects, due to short-range spin correlations. An anisotropic strain along the $\mathbf{a}$ direction was also observed below ${T}^{*}$. Below ${T}_{N}$, a relatively large contraction of the $a$ parameter following the square of the average sublattice magnetization of Mn was found, indicating that a second-order spin Hamiltonian accounts for the magnetic interactions along this direction. On the other hand, the more complex behaviors found for $b$ and $c$ suggest additional magnetic transitions below ${T}_{N}$ and perhaps higher-order terms in the spin Hamiltonian. Polycrystalline samples grown by distinct routes and with nearly homogeneous crystal structure above ${T}_{N}$ presented structural phase coexistence below ${T}_{N}$, indicating a close competition amongst distinct magnetostructural states in this compound.

High-resolution x-ray study of nematic–smectic-Aand smectic-A–reentrant-nematic transitions in liquid-crystal–aerosil gels

We have studied the effects of quenched random disorder created by dispersed aerosil nanoparticle gels on the nematic to smectic- A (N- SmA ) and smectic- A to reentrant nematic ( SmA -RN) phase transitions of thermotropic liquid-crystal mixtures of hexyloxycyanobiphenyl (6OCB) and octyloxycyanobiphenyl (8OCB). These effects are probed using high-resolution synchrotron x-ray diffraction techniques. We find that the reentrant characteristics of the system are largely unchanged by the presence of the aerosil gel network. By comparing measurements of the smectic static structure amplitude for this 8OCB- 6OCB+aerosil system with those for butyloxybenzilidene-octylaniline (4O.8)+aerosil gels, we find that the short-range smectic order in the smectic- A phase is significantly weaker in the reentrant system. This result is consistent with the behavior seen in pure 8OCB-6OCB mixtures. The strength of the smectic ordering decreases progressively as the 6OCB concentration is increased. Detailed line shape analysis shows that the high- and low-temperature nematic phases (N and RN) are similar to each other.

Synchrotron X-ray studies of austenite and bainitic ferrite

High-resolution synchrotron X-ray diffraction has been used to conduct in situ studies of the temporal evolution of phases during the isothermal growth of bainite. Two populations of austenitic material were identified: one corresponding to the initial austenite and the other to the carbon-enriched austenite associated with the bainitic ferrite. The observed lattice parameters and the asymmetry of the peaks from the residual austenite have been interpreted in terms of the carbon partitioning due to the transformation. The results are contrasted with an earlier study in which the austenite unit cell appeared to split into two distinct densities prior to the onset of transformation.

Triplet dimerization crossover driven by magnetic frustration inIn2VO5

${\mathrm{In}}_{2}\mathrm{V}{\mathrm{O}}_{5}$, containing magnetically frustrated zigzag chains, shows a remarkable crossover at $120\phantom{\rule{0.3em}{0ex}}\mathrm{K}$ between paramagnetic states with positive $(17\phantom{\rule{0.3em}{0ex}}\mathrm{K})$ and negative $(\ensuremath{-}70\phantom{\rule{0.3em}{0ex}}\mathrm{K})$ Weiss temperatures. Magnetic moment and entropy data show that the ${\mathrm{V}}^{4+}$ $S=1∕2$ spins condense into $S=1$ triplet dimers below the crossover. A further freezing of the antiferromagnetically coupled triplet dimers into a global singlet state is observed at $2.5\phantom{\rule{0.3em}{0ex}}\mathrm{K}$, with no long range magnetic order down to $0.42\phantom{\rule{0.3em}{0ex}}\mathrm{K}$ and in fields up to $9\phantom{\rule{0.3em}{0ex}}\mathrm{T}$. No structural V-V dimerization is observed by high-resolution synchrotron x-ray diffraction down to $10\phantom{\rule{0.3em}{0ex}}\mathrm{K}$, but a subtle lattice anomaly evidences a spin-lattice coupling in the triplet dimer state. This is assigned to longitudinal oxygen displacement modes that reduce frustration within the chains and so couple to the spin dimer fluctuations.