High Resolution Synchrotron Radiation Diffraction Research Articles

Structural elucidation of the degradation mechanism of nickel-rich layered cathodes during high-voltage cycling.

Phase transition occurring during cycling plays a fundamentally important role in the cycling performance of nickel-rich cathodes. Here, splitting of two O3 phases, rather than the often observed O1 phases in the conventional LiCoO2 electrode, was discovered in LiNi0.85Co0.10Mn0.05O2 at a high-voltage region (>4.6 V). Such degradation could be mitigated via Al doping.

(De)Lithiation Mechanism of Hierarchically Layered LiNi1/3Co1/3Mn1/3O2 Cathodes during High-Voltage Cycling

In view of the requirements for high-energy lithium ion batteries (LIBs), hierarchically layered LiNi1/3Co1/3Mn1/3O2 (NCM111) cathode materials have been prepared using a hydroxide coprecipitation method and subsequent high-temperature solid-state reaction. The diffraction results show that the synthesized NCM111 has a well-defined layered hexagonal structure. The initial specific discharge capacity of a Li/NCM111 cell is 204.5 mAh g−1 at a current density of 28 mA g−1 between 2.7 and 4.8 V. However, the cell suffers from poor capacity retention over extended charge-discharge cycles. The structural evolution of NCM111 electrode during electrochemical cycling is carefully investigated by in situ high-resolution synchrotron radiation diffraction. It is found that the nanodomain formation of a layered hexagonal phase H3 and a cubic spinel phase after charging to voltages above 4.6 V is the main source for the structural collapse in c direction and the poor cycling performance. This process is accompanied by the removal of oxygen, the transition metal (TM) migration and the crack generation in the nanodomains of the primary particles. These results may help to better understand the structural degradation of layered cathodes in order to develop high energy density LIBs.

Distortion of the crystal structure of MnO at ambient conditions

High resolution synchrotron radiation diffraction studies of polycrystalline powder MnO show a systematic distortion from the standard NaCl-type cubic structure (space group Fm3¯m). Two models of the distortion of MnO crystallites are presented: (i) anisotropic Bragg peak broadening due to a distribution of internal microstrains, and (ii) a model with tetragonal symmetry (space group I4/mmm) with at≈ac/√2, ct≈ac. Both models show good agreement with the experimental data which is significantly better than the cubic model with isotropic Bragg peak broadening. Both models imply a distortion of the cubic symmetry of the MnO crystal structure. The size of the tetragonal distortion is x=ct/(at√2)=1±Δ, where Δ≈2×10−4 at ambient conditions. Both tetragonal structures with elongation along ct (x=1+Δ) and shrinking along ct (x=1−Δ) give the same fit quality estimators. The distortion from cubic symmetry increases with milling time for powder MnO samples milled in a planetary mill. The proposed tetragonal space group I4/mmm has a group-subgroup relation with the monoclinic space group C2/m observed in MnO below TN.

Monoclinic deformation of the crystal lattice of hematite α-Fe2O3

Lineshape analysis of high resolution synchrotron radiation diffraction patterns of polycrystalline α-Fe2O3 powders show distortions from trigonal (space group R-3c) symmetry. The symmetry lowering is observed for α-Fe2O3 polycrystalline powders from several commercial vendors. The experimental observations can be explained by assuming a monoclinic symmetry (space group C2/c). The relative differences between the monoclinic and the hexagonal lattice constants are of the order of 10−4. The monoclinic symmetry of the crystal structure of α-Fe2O3 (C2/c) is in agreement with magnetic space group analysis [American Mineralogist 95 (2010) 974].

Transformation stress induced metastable tetragonal phase in (93–92)%Pb(Zn1/3Nb2/3)O3–(7–8)%PbTiO3 single crystals

High-resolution synchrotron radiation diffraction results indicate that the room temperature tetragonal (T) phase in (93–92)%Pb(Zn1/3Nb2/3)O3–(7–8)%PbTiO3 [PZN–(7–8)%PT] single crystals is a metastable phase stabilized by the transformation-cum-cooling stress in the crystal. This is manifested by the “missing” (001)T diffractions when the diffractions were taken from (001) fractured surfaces. The stress relaxation in this case has caused the metastable (001)T domains in the surface layer to transform to the equilibrium rhombohedral phase. Temperature and particle size effects on the metastable domains have been examined and discussed. Based on the present finding, a new PZN–PT phase diagram showing extended rhombohedral+tetragonal region is proposed.

BiFeO 3: Synchrotron radiation structure refinement and magnetoelectric geometry

Presently BiFeO 3 focuses attention due to its multiferroic nature. This phase shows a highly distorted perovskite crystal structure, with R3 c crystal symmetry. Details of the crystallographic structure are required input for a detailed explanation of its remarkable magnetoelectric properties. Present report contributes a high-resolution synchrotron radiation diffraction analysis of the BiFeO 3 crystal structure. Single-phased sample was obtained by conventional solid-state reaction under bismuth atmosphere. XRD experiment was performed on beamline 2-1, Stanford Synchrotron Radiation Laboratory, with 12 keV X-rays. For data Rietveld processing, Fullprof software package was applied. Obtained cell parameters (in Å, hexagonal system description) were a = 5.57414(4); c = 13.85882(12). Group-theoretical analysis of BiFeO 3 linear magnetoelectric tensor is presented. Only transverse effect is allowed by symmetry. Axial-symmetry polycrystal ceramics cannot show linear magnetoelectric coupling.

Étude structurale par rayonnement synchrotron de superréseaux d'oxydes pérovskites

Perovskite oxides are analyzed by using high resolution synchrotron radiation diffraction. The diffraction profiles are fitted, taking into account the structural and chemical disorders which depart from the ideal defect-free superlattice. Two types of superlattices, (BaTiO 3 /SrTiO 3 ) 15 and (La 0.7 Sr 0.3 MnO 3 /SrTiO 3 ) 15 , are synthesized by metal-organic chemical vapor deposition (MOCVD) on oriented Nb-doped SrTiO 3 substrates. High-angle diffraction data show the excellent crystallinity and epitaxy of the films. For the (BaTiO 3 /SrTiO 3 ) n multilayers we observe a pseudo tetragonal symmetry with no difference between a and b axes, and they present a significant strontium/baryum interdiffusion. The (La 0.7 Sr 0.3 MnO 3 /SrTiO 3 ) n multilayers and their substrates almost have the same a=b parameter. Along the c axis, La 0.7 Sr 0.3 MnO 3 and SrTiO 3 have different lattice parameters. The crystallographic coherence of the stacking is higher in these samples.

Measurement of the lattice misfit of the nickel-base superalloy SC16 by high-energy synchrotron radiation

High-energy, high-resolution synchrotron radiation diffraction was successfully used to measure the lattice misfit in the single-crystal nickel-base superalloy SC16. A three-peak model, one belonging to the precipitate phase γ′ and two to the matrix γ, was used to fit the diffraction peaks. Room-temperature (RT) contour plots and a temperature scan up to 1170 K revealed that the misfit evolves together with the measured thermal expansion difference between the γ and γ′ phases. This suggests that the origin of the misfit lies in the different thermal expansion coefficient of the two phases. The misfit was found to be positive at RT and to evolve toward negative values as the temperature increases.

Phase Identification in Rapidly Solidified Al-In Alloys Using High Resolution Synchrotron Radiation Diffraction and Transmission Electron Microscopy

ABSTRACTA metastable (face centered) cubic form of indium has been identified in melt-spun Al-4.3at% indium using high resolution synchrotron radiation diffraction. The microstructure of the melt-spun ribbons consisted of particles of nominally pure indium dispersed in an aluminum matrix. These particles ranged in size from 10 nm to 1000 nm through the thickness of the ribbons. Only the smallest indium particles were identified as being cubic and these were observed in electron transparent regions of the as-spun ribbons. The cubic indium phase had the following orientation relationship with the matrix: [001]In′ // [001]Al and (100)In′ // (001)Al. The size distribution and average diameter of the cubic particles were obtained by quantitative analysis of the diffraction line profiles. These measurements were corroborated with transmission electron microscopy observations. The volume percent of the cubic indium phase was determined by matching simulations of the x-ray diffraction patterns with the diffracted intensities found experimentally. Approximately 10–20% of the indium is present in the cubic form and the remainder is the stable tetragonal phase.