High-resolution Synchrotron X-ray Diffraction Research Articles

Stabilization of the pyrochlore phase of Mn2Sb2O7 by double substitution

Polycrystalline samples of (Ce4+Mn2+3)(Ga3+Sb5+3)O14 were synthesized by a high-temperature solid-state reaction. In contrast with the parent Mn2Sb2O7 compound that adopts a rhombohedral or monoclinic structure at T > 600 °C, the pyrochlore structure of CeMn3GaSb3O14 is retained up to at least T = 1070°C. High-resolution synchrotron x-ray diffraction measurements show no sign of a superstructure or distortion from cubic symmetry in the substituted compound. The stabilization of the pyrochlore structure can be attributed to the effect of configurational disorder due to partial substitution of A and B site. Magnetization and heat capacity data suggest a spin-glass transition below T ≈ 2 K. Our results extends the range of available pyrochlore oxides, and demonstrate that entropic stabilization is a viable route to stabilize novel materials with complex structure types.

Protein/Ice Interaction: High-Resolution Synchrotron X-ray Diffraction Differentiates Pharmaceutical Proteins from Lysozyme.

Protein/ice interactions are investigated by a novel method based on measuring the characteristic features of X-ray diffraction (XRD) patterns of hexagonal ice (Ih). Aqueous solutions of four proteins and other solutes are studied using high-resolution synchrotron XRD. Two pharmaceutical proteins, recombinant human albumin and monoclonal antibody (both at 100 mg/mL), have a pronounced effect on the properties of ice crystals, reducing the size of the Ih crystalline domains and increasing the microstrain. Lysozyme (100 mg/mL) and an antifreeze protein (1 mg/mL) have much weaker impact on Ih. Neither of the proteins studied exhibit preferred interactions with specific crystalline faces of Ih. It is proposed that the pharmaceutical proteins interact with ice crystals indirectly by accumulating in the quasi-liquid layer next to ice crystallization front, rather than directly, via a sorption on ice crystals. This is the first report, to the best of our knowledge, of major difference in the protein/ice interaction between non-antifreeze proteins. Another important finding is a detection of a second (minor) population of ice crystals, which is tentatively identified as a high-pressure form of ice, possibly IceIII or IceIX. This finding highlights a potential role of mechanical stresses in freeze-induced destabilization of proteins.

Variation of elastic mechanical properties with texture, porosity, and defect characteristics in laser powder bed fusion 316L stainless steel

Elastic mechanical properties of 316 L stainless steel samples fabricated using laser powder bed fusion were studied non-destructively through resonant ultrasound spectroscopy. Samples in five different conditions were obtained by varying the laser power from 103 W (the highest density condition) to 68 W (the lowest density condition) at constant laser speed, producing samples with a volume energy density in the 24.5–16.5 J/mm3 range and volumetric porosity in the 0.1–10% range. The observed elastic mechanical properties are discussed taking into consideration the bulk texture developed and quantitative pore characteristics studied using high-energy high-resolution synchrotron X-ray diffraction and X-ray computed micro-tomography, respectively. Furthermore, empirical exponential relationships are provided to express the functional dependence of Young's and shear moduli with porosity.

Electric field and temperature induced local polarization switching and piezoresponse in Bi0.88Sm0.12FeO3 ceramics for nanoscale applications

The fundamental understanding of polarization switching in ferroelectric materials is very critical for the development of ferroelectric devices. Electric field and temperature induced nanoscale polarization switching has been studied in polycrystalline Bi0.88Sm0.12FeO3 ceramics using piezoresponse force microscopy (PFM). High resolution synchrotron X-ray diffraction, Rietveld refinements and micro-Raman spectra indicate the phase coexistence of rhombohedral R3c and orthorhombic PbZrO3-like structures at room temperature. Temperature dependent Raman spectra exhibit nonpolar Pnma phase-like vibrational bands at 175 °C. The PFM amplitude and phase images revealed irregular multi-grain and domain boundaries with oppositely oriented polarizations which are 180° apart in-phase. Step-wise application of negative and positive tip biases indicates that the 109° polarization switching is more favorable at low fields due to large electric and activation energies associated with 180° switching. PFM in-plane (IP) and out-of-plane (OP) images at different temperatures show the 180° domain growth up to 150 °C. The drastic change in the in-plane phase contrast at 175 °C indicates the formation of 71° ferroelastic domains affirming the phase transition. Temperature dependent phase and amplitude measurements exhibit typical hysteresis and butterfly loops below the transition temperature signifying ferroelectric-like piezoelectric behavior. The sudden decrease in the amplitude value at 175 °C supports a phase transition to non-polar phase where piezoeresponse would be nearly zero. However, there exist non-zero piezoresponse regions at 200 °C implying that ferroelectric clusters are embedded in nonpolar phase which make the material ferroelectrically active at nanoscale level.

Shear strain-induced anisotropic domain evolution in mixed-phase BiFeO3 epitaxial films

Understanding and controlling the domain evolution under external stimuli in multiferroic thin films is critical to realizing nanoelectronic devices, including for non-volatile memory, data storage, sensors, and optoelectronics. In this article, we studied the shear-strain effect on the domain evolution with temperature in highly strained BiFeO3 thin films on rhombohedral LaAlO3 substrates using a high-resolution synchrotron X-ray diffraction three dimensional-reciprocal space mapping (3D-RSM) technique. The results revealed significant biaxial, anisotropic, evolution behaviors of the mixed-phase (MC + R′/T′ phases) BiFeO3 ferroelectric domains along the in-plane [100] and [010] axes. These biaxial, anisotropic, evolution behaviors were attributed to the shear-strain-modulated transition pathways of the mixed-phase ferroelectric domains. This viewpoint was further verified in the BiFeO3/LaSrAlO4 (001) system in which no anisotropic evolution behaviors of the mixed-phase domains were found. This work sheds light on the quantitative analysis of domain evolution in multi-domain systems and demonstrates that the shear-strain effect could act as an effective tool to manipulate the domain behavior and control novel functionalities of ferroelectric thin films.

Magneto-volume effect and magnetic properties in DyFe12−xTax compounds

Abstract The structural and magnetic properties of DyFe12−xTax compounds (with x = 0.5, 0.6, 0.65 and 0.7) have been investigated in detail using dc magnetization, differential scanning calorimetry, Mossbauer effect spectroscopy (5–300 K) and high-resolution synchrotron x-ray diffraction (10–700 K). The easy magnetization directions at room temperature are along the c-axis. With decreasing temperature, the magneto-crystalline anisotropy changes from easy axis at room temperature to easy cone at Tsr2 for all compounds, then to easy plane at Tsr1. Both Tsr1 and Tsr2 change significantly over the ranges 158–216 K and 239–259 K with increasing Ta content (x = 0.5–0.7) respectively, while the Curie temperature is found to remain essentially unchanged with a value of ∼540 K. Pronounced magneto volume effects have been detected at the Curie temperature while no clear anomalies are observed around the spin reorientation temperatures. Large spontaneous magnetostriction has been detected below TC for all of the compounds.

Improved microstructure and ferroelectric properties in B-site Ti4+-substituted (Bi0.86Sm0.14)FeO3 polycrystalline ceramics

Abstract Multiferroic ( Bi 0.86 Sm 0.14 ) ( Fe 1 − x Ti x ) O 3 ceramics (BFO14Sm100xTi) for x = 0.000 , 0.005 , and 0.010 were synthesized using solid-state reaction method to investigate the influence of Ti4+ doping on their microstructure, dielectric, and ferroelectric behaviors. Scanning electron micrographs reveal that the Ti4+ doping facilitates slow oxygen ion diffusion leading to reduced grain size (2.13, 1.75, and 1.50 μm for BFO14Sm, BFO14Sm0.5Ti, and BFO14Sm1Ti, respectively). High-resolution synchrotron X-ray diffraction (HR-XRD) analysis and Rietveld refinements confirm the phase coexistence of polar R3c rhombohedral and nonpolar PbZrO3-like Pbam orthorhombic phases. The temperature dependent HR-XRD shows that the Ti4+ ions stabilize phase coexistence up to 250 °C . The enhanced dielectric homogeneity and decreased conductivity are caused by Ti4+ substitution, which are attributed to reduction of oxygen vacancies. The improved piezoelectric coefficients (d33) and symmetric P–E hysteresis loops of BFO14Sm0.5Ti, and BFO14Sm1Ti indicate enhanced ferroelectric order due to Ti4+ ion doping.

Unraveling the physical properties and superparamagnetism in anti-site disorder controlled Fe2TiSn

With an aim to control the anti-site disorder between Fe and Ti atoms in the full Heusler alloy, FeTiSn, we substitute a small percentage of Ti at Fe site to form the FeTiSn () series. Using the incident x-rays tuned to the Fe K-edge absorption energy, we record the high resolution synchrotron x-ray diffraction profiles and unambiguously show the reduction in anti-site disorder. In particular, the Fe–Ti anti-site disorder decreases up to an excess Ti content of 0.07; further increase of Ti content leads to disorder between Ti–Sn sites. Detailed characterization vis-á-vis the excess Ti content has been carried out in terms of its thermal and electrical transport, and magnetic properties. Signatures of strong spin fluctuation are seen in all the physical properties reported here. The much disputed high value of the Sommerfeld constant has been shown to be a resultant of such strong spin fluctuations, thus ruling out the long standing controversy of heavy fermionic nature of FeTiSn. Magnetization and the Seebeck coefficient show clear dependence on the disorder. Both dc and ac magnetic measurements reveal the low temperature superparamagnetic nature of this system, comprising of large magnetic clusters 3 nm in size.

Raman scattering of impact diamonds

We report the results of a study of the polycrystalline powder of the diamond-lonsdaleite from the Popigai crater (Siberia) using UV micro-Raman spectroscopy and high-resolution synchrotron X-ray diffraction. By subtracting two experimental Raman spectra of diamond-lonsdaleite samples with close amounts of diamond and lonsdaleite, we were able to identify the polytypic composition of impact diamonds in contrast to the method of X-ray diffraction. We have managed to get for the first time the spectrum of “pure” lonsdaleite. Its deconvolution has allowed us to identify all the three Raman - active vibrational modes E2g, A1g, and E1g whose positions agree well with the results of ab initio calculations.

Structures, Phase Fields, and Mixed Protonic-Electronic Conductivity of Ba-Deficient, Pr-Substituted BaZr0.7Ce0.2Y0.1O3-δ.

The BaZr0.7Ce0.2Y0.1O3-δ-BaPrO3-δ perovskite system, of interest for high-temperature electrochemical applications involving mixed protonic-electronic conductivity, forms a solid-solution with a wide interval of Ba substoichiometry in the range Ba(Ce0.2Zr0.7)1- xPr xY0.1O3-δ, 0 ≤ x ≤ 1. Structural phase transitions mapped as a function of temperature and composition by high-resolution neutron powder diffraction and synchrotron X-ray diffraction reveal higher symmetry for lower Pr content and higher temperatures, with the largest stability field observed for rhombohedral symmetry (space group, R3̅ c). Rietveld refinement, supported by magnetic-susceptibility measurements, indicates that partitioning of the B-site cations over the A and B perovskite sites compensates Ba substoichiometry in preference to A-site vacancy formation and that multiple cations are distributed over both sites. Electron-hole transport dominates electrical conductivity in both wet and dry oxidizing conditions, with total conductivity reaching a value of ∼0.5 S cm-1 for the x = 1 end-member in dry air at 1173 K. Higher electrical conductivity and the displacement of oxygen loss to higher temperatures with increasing Pr content both reflect the role of Pr in promoting hole formation at the expense of oxygen vacancies. In more reducing conditions (N2) and at low Pr contents, conductivity is higher in humidified atmospheres (∼0.023 atm pH2O) indicating a protonic contribution to transport, whereas the greater electron-hole conductivity with increasing Pr content results in lower conductivity in humidified N2 due to the creation of protonic defects and the consumption of holes.

Order-disorder phenomena and octahedral tilting in SrTi1-XSnXO3 perovskites – A structural and spectroscopic study

Oxides of the type SrTi1-xSnxO3 have been prepared using both a solid state and polymeric precursor method and characterized using high-resolution Synchrotron X-ray Diffraction and X-ray Absorption and Raman spectroscopies. The diffraction measurements demonstrate that a continuous pseudo-solid solution exists between the cubic SrTiO3 and orthorhombic SrSnO3 end-members with the same sequence of structures cubic Pm3̅m → tetragonal I4/mcm → orthorhombic Imma → orthorhombic Pnma being observed irrespective of the preparation method. The Raman and XAS measurements revealed the presence of extensive disorder in samples treated at low temperatures, and that this disorder is reduced, but not totally eliminated, by annealing above 1300 °C. It is likely the local structure evolves similarly to that established by S-XRD for samples annealed above 1300 °C. This postulate is supported by the Ti K-edge XANES measurements that showed the local symmetry of the Ti cation evolves systematically as Sn4+ ions replace the Ti4+cations in the samples, irrespective of the temperature to which the sample had been heated.

Probing the intrinsic and extrinsic origins of piezoelectricity in lead zirconate titanate single crystals

The physical origin of the piezoelectric effect has been the focus of much research work. While it is commonly accepted that the origins of piezoelectricity may be intrinsic (related to the change of lattice parameters) and extrinsic (related to the movement of domain walls), their separation is often a challenging experimental task. Here in situ high-resolution synchrotron X-ray diffraction has been combined with a new data analysis technique to characterize the change of the lattice parameters and domain microstructure of a PbZr1−x Ti x O3 (x = 0.45) crystal under an external electric field. It is shown how `effective piezoelectric coefficients' evolve upon the transition from purely `intrinsic' effects to `extrinsic' ones due to domain-wall motion. This technique and corresponding data analysis can be applied to broader classes of materials and provide important insights into the microscopic origin of their physical properties.

Structure determination and crystal chemistry of large repeat mixed-layer hexaferrites.

Hexaferrites are an important class of magnetic oxides with applications in data storage and electronics. Their crystal structures are highly modular, consisting of Fe- or Ba-rich close-packed blocks that can be stacked in different sequences to form a multitude of unique structures, producing large anisotropic unit cells with lattice parameters typically >100 Å along the stacking axis. This has limited atomic-resolution structure solutions to relatively simple examples such as Ba2Zn2Fe12O22, whilst longer stacking sequences have been modelled only in terms of block sequences, with no refinement of individual atomic coordinates or occupancies. This paper describes the growth of a series of complex hexaferrite crystals, their atomic-level structure solution by high-resolution synchrotron X-ray diffraction, electron diffraction and imaging methods, and their physical characterization by magnetometry. The structures include a new hexaferrite stacking sequence, with the longest lattice parameter of any hexaferrite with a fully determined structure.

Local structure and lattice covalency of complex perovskites BaM0.2Ta0.8O3−xNx (M = Li, Na, Mg) studied by X-ray diffraction and X-ray absorption spectroscopy

Local structural aspects of complex perovskites BaM0.2Ta0.8O3−xNx (M = Li, Na, Mg) were studied by the extended X-ray absorption fine structure (EXAFS) and X-ray absorption near edge structure (XANES) spectroscopies at the Ta L3-edge, and also by the diffraction line broadening analysis of high-resolution synchrotron X-ray diffraction (XRD) data. The line broadening analysis based on the Williamson-Hall method indicated that the lattice periodicity of BaM0.2Ta0.8O3−xNx are disturbed remarkably, with a dependence on the size mismatch between M+/2+ and Ta5+. The Ta L3-edge EXAFS revealed that part of the Ta−O/N bonds are contracted by the existence of the large alkali cation on the shared octahedral site. Meanwhile, the XANES implied the distortion of Ta(O,N)6 from ideal octahedral geometry, where the curve fitting of the spectra provided additional information on the bonding character of Ta.

Real time in situ x-ray diffraction study of the crystalline structure modification of Ba0.5Sr0.5TiO3 during the post-annealing

We report about an in situ study of crystalline structural changes during thermal treatment of a Ba0.5Sr0.5TiO3 (BSTO) film grown on MgO. The study covers the complete cycle of heating, annealing and cooling and reveals simultaneous phenomena of phase transitions and strain evolution, which have been characterized by in situ 2D reciprocal space mapping (2D-RSM) using high-resolution synchrotron x-ray diffraction in coplanar and grazing incidence geometries. In this way, temperature induced phase transformation from the BSTO2 to the BSTO1 phase has been monitored and the appearance of a further crystalline phase was detected. Moreover, for both BSTO phases, transitions between in-plane compressive and tensile states have been determined during thermal treatment. Furthermore, a contraction of the out-of-plane lattice components has been observed during the annealing phase while the in-plane lattice components remain leading to the change of the residual in-plane strain towards tensile state. The in situ 2D-RSM findings provide valuable and versatile insights into strain engineering and structure modification upon thermal treatment.

Doped Sr2FeIrO6-Phase Separation and a Jeff ≠ 0 State for Ir5.

High-resolution synchrotron X-ray and neutron powder diffraction data demonstrate that, in contrast to recent reports, Sr2FeIrO6 adopts an I1̅ symmetry double perovskite structure with an a-b-c- tilting distortion. This distorted structure does not tolerate cation substitution, with low levels of A-site (Ca, Ba, La) or Fe-site (Ga) substitution leading to separation into two phases: a stoichiometric I1̅ phase and a cation-substituted, P21/ n symmetry, a-a-c+ distorted double perovskite phase. Magnetization, neutron diffraction, and 57Fe Mössbauer data show that, in common with Sr2FeIrO6, the cation substituted Sr2- xA xFe1- yGa yIrO6 phases undergo transitions to type-II antiferromagnetically ordered states at TN ∼ 120 K. However, in contrast to stoichiometric Sr2FeIrO6, cation substituted samples exhibit a further magnetic transition at TA ∼ 220 K, which corresponds to the ordering of Jeff ≠ 0 Ir5+ centers in the cation-substituted, P21/ n symmetry, double perovskite phases.

Doping effects of Cr on the physical properties of BaFe1.9−xNi0.1CrxAs2

We present a systematic study on the heavily Cr doped iron pnictides BaFe$_{1.9-x}$Ni$_{0.1}$Cr$_{x}$As$_{2}$ by using elastic neutron scattering, high-resolution synchrotron X-ray diffraction (XRD), resistivity and Hall transport measurements. When the Cr concentration increases from $x=$ 0 to 0.8, neutron diffraction experiments suggest that the collinear antiferromagnetism persists in the whole doping range, where the N\'{e}el temperature $T_N$ coincides with the tetragonal-to-orthorhombic structural transition temperature $T_s$, and both of them keeps around 35 K. The magnetic ordered moment, on the other hand, increases within increasing $x$ until $x=$ 0.5, and then decreases with further increasing $x$. Detailed refinement of the powder XRD patterns reveals that the Cr substitutions actually stretch the FeAs$_4$ tetrahedron along the $c-$axis and lift the arsenic height away Fe-Fe plane. Transport results indicate that the charge carriers become more localized upon Cr doping, then changes from electron-type to hole-type around $x=$ 0.5. Our results suggest that the ordered moment and the ordered temperature of static magnetism in iron pnictides can be decoupled and tuned separately by chemical doping.

Structural and electronic response of overexpanded superconducting fullerides close to the Mott insulator boundary

The ternary fulleride, Rb[Formula: see text]Cs[Formula: see text]C[Formula: see text], is the most expanded member of the family of face-centered cubic (fcc) structured superconducting fullerides ever accessed with superconductivity surviving at ambient pressure closest to the Mott insulator boundary. Here, we study the evolution of its structural and electronic properties with temperature. At ambient temperature, Rb[Formula: see text]Cs[Formula: see text]C[Formula: see text] lies in the Mott–Jahn–Teller (MJT) insulating part of the phase diagram. High-resolution synchrotron X-ray diffraction shows that its structure remains strictly cubic at all temperatures, but the transition to the metallic state at [Formula: see text] 50 K — evident in the evolution of the magnetic susceptibility with temperature — is accompanied by a lattice collapse, [Formula: see text]V/V0 of [Formula: see text]. Bulk superconductivity then emerges on further cooling with a T[Formula: see text] of 25.9 K. The results permit the extension of the electronic phase diagram of A3C[Formula: see text] fullerides as close as possible to the metal–insulator (M–I) crossover.

Optimization of single crystal growth of candidate quantum spin-ice [formula omitted] by optical floating-zone method

We report the optimized conditions for growing the high quality single crystals of candidate quantum spin-ice Pr2Hf2O7 using the optical floating-zone method. Large single crystals of Pr2Hf2O7 have been grown under different growth conditions using a four-mirror type optical floating-zone furnace and their microscopic structural differences have been probed by high-resolution synchrotron X-ray diffraction (SXRD). The SXRD data reveal that the crystals grown under flowing argon (∼2 L/h) atmosphere with slightly off-stoichiometric (optimized) starting composition yields the highest quality crystals. The magnetic susceptibility, isothermal magnetization and heat capacity data of optimally grown crystals are presented.

Anomalous atomic displacement parameters and local dynamics in the Curie range of a Pb-free relaxor ferroelectric system (Bi1-xBax)(Fe1-xTix)O3(0.36 ≤ x ≤ 0.50)

We report here the relaxor ferroelectric (RFE) behaviour in a multiferroic solid solution system, (Bi1-xBax)(Fe1-xTix)O3, at a critical disorder level of xC ∼ 0.35 in BiFeO3 and 0.65 (i.e., 1-xC = 0.35) in BaTiO3 similar to the 1:2 ratio of Mg2+ and Nb5+ in the canonical RFE Pb(Mg1/3Nb2/3)O3. This Pb-free system, like canonical Pb-based RFEs, does not exhibit macroscopic symmetry breaking and shows only the signatures of ergodicity breaking at Vogel-Fulcher freezing temperature (TVF). The atomic displacement parameters (ADPs) of Fe3+/Ti4+ and O2−, obtained using high wave vector (Q) and high-resolution synchrotron x-ray diffraction data as a function of temperature, show anomalous diffuse peaks in the Curie range. It is shown that the diffuse peak in ADPs is due to softening of the vibrational frequencies of the B-O chain (B = Fe3+/Ti4+ and O = O2−) below the Burns temperature (TB) followed by hardening below the characteristic temperature (T′m), which corresponds to a peak in the dielectric permittivity (ε′).