High-resolution Synchrotron X-ray Powder Research Articles

Long- and short-range structure studies of KBT-KBZ solid-solutions using synchrotron radiation.

The relaxor ferroelectric K(0.5)Bi(0.5)TiO(3) has been synthesised in a solid-solution series with K(0.5)Bi(0.5)ZrO(3), as K(0.5)Bi(0.5)Ti1-xZrxO(3). High-resolution synchrotron X-ray powder diffraction and X-ray absorption near edge structure spectroscopy were used to characterise the long-range average and local structural behaviour. Rietveld refinements against diffraction data show that a pseudocubic tetragonal region exists across the whole solid-solution series, with truly cubic symmetry only observed at x = 1 (pure KBZ). Variable-temperature diffraction data for x = 0 (pure KBT) showed a broad ferroelectric transition from tetragonal to cubic symmetry at approximately 683 K with a coexistence of both phases close to that temperature, accompanied by a marked volume contraction. Ti K-edge data showed that Zr doping has a minimal effect on Ti off-centering, and revealed no evidence for local clustering. Metal L-edges showed that Ti(4+) cations remain off-centered with increasing Zr content, while Zr(4+) cations approach a higher-symmetry coordination environment, most likely due to the increased size of the Zr atoms. Although there is a minimal effect on actual Ti-offsets, an effective dilution of these environments by Zr doping leads to a reduction in polar domains and a diminished ferroelectric response.

Hybrid inorganic-organic materials with an optoelectronically active aromatic cation: (C7H7)2SnI6 and C7H7PbI3.

Inorganic materials with organic constituents-hybrid materials-have shown incredible promise as chemically tunable functional materials with interesting optical and electronic properties. Here, the preparation and structure are reported of two hybrid materials containing the optoelectronically active tropylium ion within tin- and lead-iodide inorganic frameworks with distinct topologies. The crystal structures of tropylium tin iodide, (C7H7)2SnI6, and tropylium lead iodide, C7H7PbI3, were solved using high-resolution synchrotron powder X-ray diffraction informed by X-ray pair distribution function data and high-resolution time-of-flight neutron diffraction. Tropylium tin iodide contains isolated tin(IV)-iodide octahedra and crystallizes as a deep black solid, while tropylium lead iodide presents one-dimensional chains of face-sharing lead(II)-iodide octahedra and crystallizes as a bright red-orange powder. Experimental diffuse reflectance spectra are in good agreement with density functional calculations of the electronic structure. Calculations of the band decomposed charge densities suggest that the deep black color of tropylium tin iodide is attributed to iodide ligand to tin metal charge transfer, while the bright red-orange color of tropylium lead iodide arises from charge transfer between iodine and tropylium states. Understanding the origins of the observed optoelectronic properties of these two compounds, with respect to their distinct topologies and organic-inorganic interactions, provides insight into the design of tropylium-containing compounds for potential optical and electronic applications.

Evolution of structure in Na0.5Bi0.5TiO3 single crystals with BaTiO3

The structural, dielectric, and piezoelectric properties of Na0.5Bi0.5TiO3-x mol. %BaTiO3 (NBT-x%BT) crystals have been investigated. The dielectric and piezoelectric properties of NBT-x%BT were enhanced near x = 5–7. High resolution synchrotron x-ray powder diffraction studies revealed the presence of a phase boundary between monoclinic (Cc) and tetragonal (P4bm) phases near x = 5–7, where the dielectric and piezoelectric properties were enhanced.

Incommensurate modulations in stoichiometric Ni2MnGa ferromagnetic shape memory alloy: an overview

Abstract This article presents a brief overview of our recent work on the nature of long period modulation in the premartensite and martensite phases of Ni2MnGa ferromagnetic shape memory alloy using high resolution synchrotron x-ray powder diffraction patterns. The commensurate structure model using the Pnnm space group is unable to account for the peak positions of the satellite reflections that appear due to modulations correctly. LeBail and Rietveld refinements using the (3+1)-D super space group Immm(00γ)s00 show that the peak positions of all the reflections, including the satellites, can be explained satisfactorily using incommensurate modulations for both the premartensite and martensite phases. The incommensurate modulation vectors are found to be q =0.33761(5) c* =(1/3+δ1) c* and 0.43160(3) c* =(3/7+δ2) c* , where δ1 and δ2 are the degrees of incommensuration for the premartensite and martensite phases, respectively. The periodicity of the closest rational approximant of the premartensite and martensite phases are confirmed to be 3 M and 7 M, respectively, in agreement with single crystal diffraction results.

Cation ordering and flexibility of the BO₄²⁻ tetrahedra in incommensurately modulated CaEu₂(BO₄)₄ (B = Mo, W) scheelites.

The factors mediating cation ordering in the scheelite-based molybdates and tungstates are discussed on the basis of the incommensurately modulated crystal structures of the CaEu2(BO4)4 (B = Mo, W) red phosphors solved from high-resolution synchrotron powder X-ray diffraction data. Monoclinic CaEu2(WO4)4 adopts a (3 + 1)-dimensionally modulated structure [superspace group I2/b(αβ0)00, a = 5.238 73(1)Å, b = 5.266 35(1) Å, c = 11.463 19(9) Å, γ = 91.1511(2)°, q = 0.56153(6)a* + 0.7708(9)b*, R(F) = 0.050, R(P) = 0.069], whereas tetragonal CaEu2(MoO4)4 is (3 + 2)-dimensionally modulated [superspace group I4₁/a(αβ0)00(-βα0)00, a = 5.238 672(7) Å, c = 11.548 43(2) Å, q1 = 0.55331(8)a* + 0.82068(9)b*, q2 = -0.82068(9)a* + 0.55331(8)b*, R(F) = 0.061, R(P) = 0.082]. In both cases the modulation arises from the ordering of the Ca/Eu cations and the cation vacancies at the A-sublattice of the parent scheelite ABO4 structure. The cation ordering is incomplete and better described with harmonic rather than with steplike occupational modulation functions. The structures respond to the variation of the effective charge and cation size at the A-position through the flexible geometry of the MoO4(2-) and WO4(2-) tetrahedra demonstrating an alternation of stretching the B-O bond lengths and bending the O-B-O bond angles. The tendency towards A-site cation ordering in scheelites is rationalized using the difference in ionic radii and concentration of the A-site vacancies as parameters and presented in the form of a structure map.

Structural transformations in R3Cu4Sn4 (R = Ho, Er, Tm) intermetallic compounds

The family of ternary intermetallic compounds R3T4X4 (R = rare-earth; T = d-element; X = Si, Ge, Sn) comprises over 100 members that have a generic orthorhombic structure (space group Immm, #71) at room temperature. We have observed a monoclinic ↔ orthorhombic crystallographic transformation in Ho3Cu4Sn4, Er3Cu4Sn4 and Tm3Cu4Sn4 by high-resolution synchrotron X-ray and neutron powder diffraction. We show that the temperature at which this transformation occurs scales linearly with the ionic radius of the rare-earth. No such transformation was observed in Dy3Cu4Sn4, down to 1.7 K, consistent with this scaling.

Locating Cu in Zeolite SSZ-13 by Synchrotron PXRD Using Maximum Entropy Method

Efficient elimination of environmentally harmful gaseous NOx compounds from automotive diesel emission remains a challenging task. State-of-the-art zeolites with the chabazite framework containing catalytically active Cu2+ (Cu-SSZ-13) have been commercialized as NOx after-treatment catalysts in diesel-powered vehicles, due to its superior activity, selectivity, and durability.[1] However, to meet current and future legislative demands, continuous improvement is of fundamental interest. Prerequisites for an in depth understanding and further improvements, are detailed complete structural models of the Cu-loaded catalyst. This may be achieved by the use of high resolution synchrotron powder X-ray diffraction (PXRD) and iterative Rietveld analysis and Maximum Entropy Method (MEM). Since the content of Cu2+ is low, a protonated system (H-SSZ-13) and model system with monovalent Ag+ ions (Ag-SSZ-13) are also examined. The protonated and dehydrated H-SSZ-13 shows perfectly empty voids, i.e. no water residue or other non-framework species. The H-SSZ-13 structure is used as the initial model for the MEM calculations. For Ag-SSZ-13 MEM analysis clearly pinpoints the Ag+ ion as being located in the 6-ring shifted into the chabazite cage (Figure 1), consistent with the generally accepted site for Ag+ ions in chabazite and reveals the strength of the iterative Rietveld/MEM analysis. For the more challenging case of Cu-SSZ-13 it was still possible through careful analysis and reasoning to locate two separate positions for the Cu2+ in Cu-SSZ-13 (Figure 1). The B site has been suggested by several other studies, but never confirmed experimentally.[2] This is the most complete structural description of zeolite SSZ-13 with stabilizing and catalytically active Cu2+ ions.[3]

Magnetoelastic driven Negative Thermal Expansion in a Framework Antiferromagnet

Metal-organic frameworks (MOFs) have recently attracted great attention for their multiferroic, magnetocaloric and low dimensional magnetic order. These properties depend on the precise magnetic interactions in frameworks and a deeper understanding of the coupling between the lattice of these materials and their magnetic order is required to underpin the future developments of these promising compounds. Neutron diffraction is the ideal technique for such studies but its application to studies of the magnetic structure of MOFs has been limited to date due to challenges in solving the structure of these dilute yet complex magnetic compounds. We have recently examined the magnetic properties and structure of a new dicarboxylate framework, cobalt adipate, Co(C6H8O4), which adopts P21/c monoclinic symmetry.[1] This compound has been found to order antiferromagnetically at low temperature and fits to neutron diffraction data have shown it adopts Pb21/c magnetic symmetry. Its magnetic structure features sheets of Co cations coupled antiferromagnetically in two dimensions through carboxylate groups. The emergence of this order is accompanied by magnetoelastic coupling, which drives anisotropic negative thermal expansion along the a-axis at low temperature. This is the first evidence for such behaviour in a MOF and we find that both this behaviour and the spin orientation in this material are controlled by the presence of weak ferromagnetic dipole-dipole coupling between the layers of tetrahedral cobalt. Variable temperature high resolution synchrotron X-ray and neutron powder diffraction have also revealed that the monoclinic angle of Co adipate decreases on cooling, passing through a metrically orthorhombic phase without any indication of a phase transition. This unusual behaviour has been rationalised by examining the thermal expansion of the framework along its principal axis, highlighting the importance of such analysis in low symmetry materials.

Two types of adjacent dimer layers in the low-temperature phase of BaCuSi2O6

The low-temperature crystal structure of BaCuSi2O6has been investigated with high-resolution synchrotron x-ray and neutron powder diffraction techniques and has been found to be on average (ignoring the incommensurate modulation) orthorhombic, with the most probable space group Ibam. The Cu-Cu dimers in this material are forming two types of layers with distinctly different interatomic distances. Subtle changes also modify the partially frustrated interlayer Cu-Cu exchange paths. The present results corroborate the interpretation of low-temperature nuclear magnetic resonance and inelastic neutron scattering data in terms of distinct dimer layers. The experimentally determined low-temperature crystal structure of BaCuSi2O6is discussed in terms of its relation to the newer findings of theory and of the complementary experiments.

When two bad data sets are better than one

High-resolution synchrotron X-ray powder diffraction (SXPD) data alone are sometimes not enough to solve the structure of a complex polycrystalline material. Such was the case for the high-silica zeolites SSZ-61 and SSZ-87, where combining data from different sources, in particular XPD and electron microscopy, was vital to success. For SSZ-61, the SXPD data feature broad peaks and a resolution of ca. 1.2 Å. Although the pattern could be indexed, structure determination failed both with the charge flipping routine in SUPERFLIP [1] and with the zeolite-specific program FOCUS [2]. The unit cell parameters and HRTEM images indicated a relationship with ZSM-12 (MTW) and SSZ-59 (SFN), so several models derived from these two frameworks were built. Eventually, after considering Si-29 MAS NMR data and the size of the organic structure directing agent (SDA), a framework model that fits all the data emerged. To complete the structure, the SDA was included as a rigid-body, and its location and orientation optimized using simulated annealing. Subsequent Rietveld refinement confirmed the structure. In contrast to SSZ-61, the SXPD pattern for SSZ-87 was quite good, and it could be indexed with a C-centered cell. However, structure solution failed, probably because of the very high degree of reflection overlap (93%). Therefore, rotation electron diffraction (RED) data [3] were collected, but they proved to be of low resolution and poor quality. Only 2 of the 7 data sets could be indexed, and these had different unit cells. Neither fit the XPD pattern directly. The problem was traced to large errors in the RED cell parameters, and eventually one RED cell could be transformed to one similar to the SXPD cell. The RED data with this cell was only 15% complete up to a resolution of 1.22 Å. Even so, the structure could be solved using a recently developed version of FOCUS that works with ED data. The SDA was found as for SSZ-61, and the structure then confirmed by Rietveld refinement.

High-resolution synchrotron x-ray powder diffraction study of the incommensurate modulation in the martensite phase ofNi2MnGa: Evidence for nearly 7M modulation and phason broadening

The modulated structure of the martensite phase of Ni2MnGa is revisited using high resolution synchrotron x-ray powder diffraction (SXRPD) measurements, which reveals higher order satellite reflections up to the 3rd order and phason broadening of the satellite peaks. The structure refinement, using the (3+1) dimensional superspace group approach, shows that the modulated structure of Ni2MnGa can be described by orthorhombic superspace group Immm(00$\gamma$)s00 with lattice parameters a= 4.21861(2) {\AA}, b= 5.54696(3) {\AA}, and c= 4.18763(2) {\AA} and an incommensurate modulation wave vector q= 0.43160(3)c*= (3/7+$\delta$)c*, where $\delta$=0.00303(3) is the degree of incommensuration of the modulated structure. Additional satellite peak broadening, which could not be accounted for in terms of the anisotropic strain broadening based on a lattice parameter distribution , has been modeled in terms of phasons using fourth rank covariant strain tensor representation for incommensurate structures. The simulation of single crystal diffraction patterns from the refined structural parameters unambiguously reveals a rational approximant structure with 7M modulation. The inhomogeneous displacement of different atomic sites on account of incommensurate modulation and the presence of phason broadening clearly rule out the adaptive phase model proposed recently by Kaufmann et al.[1] and suggests that the modulation in Ni2MnGa originates from soft-mode phonons.

Incorporation of a Recombinant Biomineralization Fusion Protein into the Crystalline Lattice of Calcite

High-resolution synchrotron X-ray powder diffraction (XRD) combined with the Rietveld refinement method and confocal laser scanning microscopy (CLSM) were utilized in this study to elucidate the interaction between a recombinant biomineralization protein (perlucin) fused to green fluorescent protein (GFP) and synthetic calcite. Although recombinant perlucin is insoluble, its solubility was increased via fusion to the highly soluble GFP. We demonstrate that GFP-perlucin derivatives become incorporated into the calcite structure and induce concentration-dependent anisotropic lattice distortions along the host’s c-axis. In contrast, GFP alone is hardly incorporated at all. The observed lattice distortions and peculiar microstructure of the crystals are comparable to those previously observed in biogenic calcite. Taking advantage of biotechnology to optimize individual protein properties, such as the solubility of an otherwise insoluble protein derivative, is a promising route toward the synthesis of new and improved biocomposite materials.

A New Microporous Zeolitic Silicoborate (ITQ-52) with Interconnected Small and Medium Pores

A new zeolite (named as ITQ-52) having large cavities and small and medium channels has been synthesized. This was achieved by using a new family of amino-phosphonium cations as organic structure directing agents (OSDA). These cations contain P-C and P-N bonds, and therefore they lie between previously reported P-containing OSDA, such as tetraalkylphosphonium and phosphazenes. In this study, it has been found that 1,4-butanediylbis[tris(dimethylamino)]phosphonium dication is a very efficient OSDA for crystallization of several zeolites, and in some particular conditions, the new zeolite ITQ-52 was synthesized as a pure phase. The structure of ITQ-52 has been solved using high-resolution synchrotron X-ray powder diffraction data of the calcined solid. This new zeolite crystallizes in the space group I2/m, with cell parameters a = 17.511 Å, b = 17.907 Å, c = 12.367 Å, and β = 90.22°. The topology of ITQ-52 can be described as a replication of a composite building unit with ring notation [4(3)5(4)6(1)] that gives rise to the formation of an interconnected 8R and 10R channel system.

Magnetization, crystal structure and anisotropic thermal expansion of single-crystal SrEr2O4

The magnetization, crystal structure, and thermal expansion of a nearly stoichiometric Sr1.04(3)Er2.09(6)O4.00(1)single crystal have been studied by PPMS measurements and in-house and high-resolution synchrotron X-ray powder diffraction.

Alloys based on Cr–Cr2Ta containing Si

Dual phase alloys containing Cr-Laves phases have been considered as potential candidates for high temperature service. In this paper, the effect of Si additions on site occupancies in Cr–Cr2Ta alloys has been studied. Calculations using density functional theory predict that Si substitutes for the Cr atoms rather than Ta within the structure and that Si and Cr are relatively free to occupy 2a and 6h sites interchangeably. However, slight non-uniformity in the 6h Si–Cr minimum charge density and bond length leads to Si favouring 2a occupation within C14 (Cr2−xSix)Ta. These predictions were supported by studies using high-resolution synchrotron X-ray powder diffraction. The effect of quaternary additions on the microstructures and elevated temperature oxidation characteristics of Cr–Ta–Si–X alloys, where X = Ag, Ti, Hf, Mo, Al and Re have also been investigated. The microstructure of the alloys comprised primarily of a eutectic mixture of a Cr-rich solid solution and Cr2Ta-based Laves phase along with primary dendrites of C14 Cr2Ta. Upon isothermal exposure of the alloys for 100 h at 1000 °C, the Re-containing alloy was found to possess the best oxidation resistance, followed by the Hf-containing alloy. The alloys exhibited a significantly superior oxidation resistance at 800 °C owing to the formation of an adherent chromia layer. The oxidation behaviour of the alloys could be described using a combination of linear and parabolic growth laws.

Chemical Inhomogeneity, Short‐Range Order, and Magnetism in the LiNiO2‐NiO Solid Solution

NiO:Li is an early exemplar for which hole-doping of a correlated insulator gives rise to rich and varied magnetic behavior. It is also an important system from the viewpoint of p-type transparent conducting oxides, and is representative of a large class of materials that have been used in lithium ion batteries, since the end-member compound, LiNiO2 , belongs to the class of layered cathode materials. Despite the deceptive structural and compositional simplicity of this system, a complete understanding of its complex magnetic properties has remained elusive. Here a comprehensive investigation of the solid solution Lix Ni2-x O2 , examining samples of precise stoichiometry using a combination of high-resolution synchrotron X-ray powder diffraction and SQUID magnetometry, is provided. The focus is on the interesting region between 0.40<x<1.00 in which the magnetic ordering temperature changes drastically with composition. The magnetism evolves from strong G-type antiferromagnetism of x=0.40 with TN =327 K to robust uncompensated magnetic order at TN =240 K when x is close to 0.7, and to glassy A-type antiferromagnetism of x=1.00 at TN =9 K. This study demonstrates this magnetic behavior is linked to the Li-Ni chemical order that develops from short- to long-range. The interfaces between ordered domains give rise to magnetic exchange bias, which manifests as a shift in the magnetization-field loop for samples with nanoscale coherence lengths (0.54<x<0.66).

Synchrotron X-ray powder diffraction study on synthetic Sr-Fresnoite

The Sr analogue of the mineral fresnoite (Sr2TiSi2O8) is of interest as a potential storage medium for radioactive Sr from nuclear waste. No high or low temperature crystal structure information is known on this phase. Therefore high-resolution synchrotron X-ray powder diffraction measurements have been done on a synthetic sample of Sr-fresnoite in the temperature range 87-1223K. This was done as a test experiment using the HRPD beamline P02.1 at PETRA-III, DESY. Synchrotron X-ray wavelengths of 0.2067(3)Å (293K and 573-1223K) and 0.2079(3)Å (87-499K) were used. Powder diffraction data were collected with a counting time of 30s using a PerkinElmer XRD 1621 flat panel image plate detector. CeO2 was included as an internal standard to calibrate the sample to detector distance. The P4bm tetragonal crystal structure of fresnoite (Ba2TiSi2O8) was used as a starting model for Sr-fresnoite. Small amounts of SrTiO3 and SrSiO3 were also found as impurities in this sample; therefore four-phase Rietveld refinements were done. The P4bm fresnoite structure is retained over the temperature range 87-1223K.

(3 + 1)D superspace description of the incommensurate modulation in the premartensite phase of Ni2MnGa: a high resolution synchrotron x-ray powder diffraction study

Le Bail and Rietveld analysis of high resolution synchrotron x-ray powder diffraction (SXRPD) data shows unambiguous signatures of the failure of the commensurate 3M modulation model. Using (3 + 1) dimensional superspace group formalism, we have not only confirmed the incommensurate modulation in the premartensite phase with a modulation wavevector of q = 0.337 61(5)c* but also determined the superspace group (Immm(00γ)s00), atomic positions and amplitude of modulations for the incommensurate premartensite phase of Ni2MnGa for the first time. Our results may have important implications in the understanding of the martensitic transition and hence the magnetic field induced strains.

Structure and Magnetic Properties of Cu3Ni2SbO6 and Cu3Co2SbO6 Delafossites with Honeycomb Lattices

The crystal structures of two Delafossites, Cu3Ni2SbO6 and Cu3Co2SbO6, are determined by high-resolution synchrotron powder X-ray diffraction. The Ni and Co are ordered with respect to Sb in the layer of edge sharing octahedra, forming magnetic layers with honeycomb geometry. High-resolution electron microscopy confirms ordering, and selected-area electron diffraction patterns identify examples of the stacking polytypes. Low temperature synthetic treatments result in disordered stacking of the layers, but heating just below their melting points results in nearly fully ordered stacking variants. The major variant in both cases is a monoclinic distortion of a 6-layer Delafossite polytype, but a significant amount of a 2-layer polytype is also present for the Ni case. The antiferromagnetic ordering with transitions, at 22.3 and 18.5 K for Ni and Co variants, respectively, is investigated by temperature and field dependent magnetization, as well as specific heat. The sharp magnetic transitions support the presence of well developed 2:1 ordering of the Co:Sb or Ni:Sb ions in the honeycomb layers. Neutron diffraction measurements at 4 K are used to determine the magnetic structures. For both the Ni and Co phases, the propagation vector is k = [100], and can be described as alternating ferromagnetic chains in the metal-oxide plane giving an overall antiferromagntic "zigzag" alignment. While orientation of the magnetic moments of the Co is along the b-axis, the Ni moments are in the ac plane, approximately parallel to the stacking direction. Bulk magnetization properties are discussed in terms of their magnetic structures.

Spin orders and lattice distortions of geometrically frustrated 6H-perovskites Ba3B′Ru2O9(B′ = La3+, Nd3+, and Y3+)

The magnetic and crystal structures of the title materials have been investigated using high-resolution neutron and synchrotron x-ray powder diffraction. Ferromagnetic Ru dimers are observed in the spin-ordered ground states of all three materials, evidencing an intradimer double exchange interaction. Antiferromagnetic order between dimers breaks the degeneracy of the triangular lattice but no distortion of the ${B}^{\ensuremath{'}}=\mathrm{La}$ and Y structures is observed. The magnetic ordering transition temperature increases with the radius of the ${B}^{\ensuremath{'}}$ cation. An anomalous 120 K structural transition in Ba${}_{3}$NdRu${}_{2}$O${}_{9}$ is attributed to Jahn-Teller distortion, evidenced by large-amplitude ${\ensuremath{\Gamma}}_{6}$ deformations of the NdO${}_{6}$ octahedra. Further lattice anomalies accompany magnetic ordering transitions at 24 and 18 K in Ba${}_{3}$NdRu${}_{2}$O${}_{9}$. Nd spins order ferromagnetically and a substantial magnetic anisotropy leads to large coercivity and $\frac{1}{3}$-magnetization steps in the magnetic hysteresis loop.