Neutron Laue Diffraction Research Articles

Neutron Laue diffraction to probe hydrogen-bonding materials

Neutron Laue diffraction to probe hydrogen-bonding materials

Floating zone crystal growth, structure, and properties of a cubic Li5.5La3Nb1.5Zr0.5O12 garnet-type lithium-ion conductor

Floating zone growth of a cm-sized solid-state electrolyte single crystal, identification of two distinct Li sites with Laue neutron diffraction, and Li-ion conductivity and migration energy determination by EIS and dielectric measurements.

Incorporation of tetrahedral ferric iron into hydrous ringwoodite

Abstract Hydrous Fo91 ringwoodite crystals were synthesized at 20 GPa and high-temperature conditions using a multi-anvil press. Recovered crystals were analyzed using electron microprobe analysis, Raman spectroscopy, infrared spectroscopy, synchrotron Mössbauer spectroscopy, single-crystal X-ray diffraction, and single-crystal Laue neutron diffraction, to carefully characterize the chemistry and crystallography of the samples. Analysis of the combined data sets provides evidence for the presence of tetrahedrally coordinated ferric iron and multiple hydrogen incorporation mechanisms within these blue-colored iron-bearing ringwoodite crystals. Tetrahedral ferric iron is coupled with cation disorder of silicon onto the octahedrally coordinated site. Cation disorder in mantle ringwoodite minerals may be promoted in the presence of water, which could have implications for current models of seismic velocities within the transition zone. Additionally, the presence of tetrahedrally coordinated ferric iron may cause the blue color of many ringwoodite and other high-pressure crystals.

Twinning in MAPbI3 at room temperature uncovered through Laue neutron diffraction

The crystal structure of MAPbI3, the signature compound of the hybrid halide perovskites, at room temperature has been a reason for debate and confusion in the past. Part of this confusion may be due to twinning as the material bears a phase transition just above room temperature, which follows a direct group–subgroup relationship and is prone to twinning. Using neutron Laue diffraction, we illustrate the nature of twinning in the room temperature structure of MAPbI3 and explain its origins from a group-theoretical point-of-view.

Super-Necking Crystal Growth and Structural and Magnetic Properties of SrTb2O4 Single Crystals.

We report on single-crystal growths of the SrTb2O4 compound by a super-necking technique with a laser-floating-zone furnace and study the stoichiometry, growth mode, and structural and magnetic properties by scanning electronic microscopy, neutron Laue, X-ray powder diffraction, and the physical property measurement system. We optimized the growth parameters, mainly the growth speed, atmosphere, and the addition of a Tb4O7 raw material. Neutron Laue diffraction displays the characteristic feature of a single crystal. Our study reveals an atomic ratio of Sr:Tb = 0.97(2):2.00(1) and a possible layer by layer crystal growth mode. Our X-ray powder diffraction study determines the crystal structure, lattice constants, and atomic positions. The paramagnetic (PM) Curie–Weiss (CW) temperature θCW = 5.00(4) K, and the effective PM moment Mmeaeff = 10.97(1) μB per Tb3+ ion. The data of magnetization versus temperature can be divided into three regimes, showing a coexistence of antiferromagnetic and ferromagnetic interactions. This probably leads to the magnetic frustration in the SrTb2O4 compound. The magnetization at 2 K and 14 T originates from both the Tb1 and Tb2 sites and is strongly frustrated with an expected saturation field at ∼41.5 T, displaying an intricate phase diagram with three ranges.

Strong hydrogen bonding in a dense hydrous magnesium silicate discovered by neutron Laue diffraction.

A large amount of hydrogen circulates inside the Earth, which affects the long-term evolution of the planet. The majority of this hydrogen is stored in deep Earth within the crystal structures of dense minerals that are thermodynamically stable at high pressures and temperatures. To understand the reason for their stability under such extreme conditions, the chemical bonding geometry and cation exchange mechanism for including hydrogen were analyzed in a representative structure of such minerals (i.e. phase E of dense hydrous magnesium silicate) by using time-of-flight single-crystal neutron Laue diffraction. Phase E has a layered structure belonging to the space group R 3 m and a very large hydrogen capacity (up to 18% H2O weight fraction). It is stable at pressures of 13-18 GPa and temperatures of up to at least 1573 K. Deuterated high-quality crystals with the chemical formula Mg2.28Si1.32D2.15O6 were synthesized under the relevant high-pressure and high-temperature conditions. The nuclear density distribution obtained by neutron diffraction indicated that the O-D dipoles were directed towards neighboring O2- ions to form strong interlayer hydrogen bonds. This bonding plays a crucial role in stabilizing hydrogen within the mineral structure under such high-pressure and high-temperature conditions. It is considered that cation exchange occurs among Mg2+, D+ and Si4+ within this structure, making the hydrogen capacity flexible.

KOALA – routine H-atom determinations by Laue neutron diffraction

KOALA – routine H-atom determinations by Laue neutron diffraction

Growth of LiCoO2 Single Crystals by the TSFZ Method

We have grown LiCoO2 single crystals by the traveling solvent floating zone (TSFZ) growth with Li-rich solvent, having observed the incongruent melting behavior of LiCoO2 between 1100 and 1300 °C. The optimum growth conditions in terms of atmosphere and solvent composition were determined to be Ar flow and an atomic ratio Li/Co 85:15, respectively. The crystals grown using a conventional-mirror-type furnace contained periodic inclusions of a Co–O phase due to the influence of Co–O phase segregation on the stability of the molten zone during growth. By using a tilted-mirror FZ furnace, inclusion-free LiCoO2 crystals of about 5 mm in diameter and 70 mm long were obtained at a tilting angle θ = 10°. The grown crystals were confirmed to be single-domain by neutron Laue diffraction.

Accurate data processing for neutron Laue diffractometers

The factors affecting the accuracy of structural refinements from image-plate neutron Laue diffractometers are analysed. From this analysis, an improved data-processing method is developed which optimizes the intensity corrections for exposure scaling, wavelength distribution, absorption and extinction corrections, and the wavelength/spatial/time dependence of the image-plate detector efficiencies. Of equal importance is an analysis of the sources of uncertainty in the final corrected intensities, without which bias of the merged intensities occurs, due to the dominance of measurements with small statistical errors though potentially large systematic errors. A new aspect of the impact of detector crosstalk on the counting statistics of area detectors is reported and shown to be significant for the case of neutron Laue diffraction. These methods have been implemented in software which processes data from the KOALA instrument at ANSTO and the now decommissioned VIVALDI instrument at ILL (Grenoble, France). A comparison with earlier data-analysis methods shows a significant improvement in accuracy of the refined structures.

Field-induced reentrant magnetoelectric phase in LiNiPO4

Using pulsed magnetic fields up to $30\phantom{\rule{0.28em}{0ex}}\mathrm{T}$ we have measured the bulk magnetization and electrical polarization of ${\mathrm{LiNiPO}}_{4}$ and have studied its magnetic structure by time-of-flight neutron Laue diffraction. Our data establish the existence of a reentrant magnetoelectric phase between $19\phantom{\rule{0.28em}{0ex}}\mathrm{T}$ and $21\phantom{\rule{0.28em}{0ex}}\mathrm{T}$. We show that a magnetized version of the zero field commensurate structure explains the magnetoelectric response quantitatively. The stability of this structure suggests a field-dependent spin anisotropy. Above $21\phantom{\rule{0.28em}{0ex}}\mathrm{T}$, a magnetoelectrically inactive, short-wavelength incommensurate structure is identified. Our results demonstrate the combination of pulsed fields with epithermal neutron Laue diffraction as a powerful method to probe even complex phase diagrams in strong magnetic fields.

Accurate hydrogen parameters for the amino acid L-leucine.

The structure of the primary amino acid L-leucine has been determined for the first time by neutron diffraction. This was made possible by the use of modern neutron Laue diffraction to overcome the previously prohibitive effects of crystal size and quality. The packing of the structure into hydrophobic and hydrophilic layers is explained by the intermolecular interaction energies calculated using the PIXEL method. Variable-temperature data collections confirmed the absence of phase transitions between 120 and 300 K in the single-crystal form.

Neutron and high-pressure X-ray diffraction study of hydrogen-bonded ferroelectric rubidium hydrogen sulfate.

The pressure- and temperature-dependent phase transitions in the ferroelectric material rubidium hydrogen sulfate (RbHSO4) are investigated by a combination of neutron Laue diffraction and high-pressure X-ray diffraction. The observation of disordered O-atom positions in the hydrogen sulfate anions is in agreement with previous spectroscopic measurements in the literature. Contrary to the mechanism observed in other hydrogen-bonded ferroelectric materials, H-atom positions are well defined and ordered in the paraelectric phase. Under applied pressure RbHSO4 undergoes a ferroelectric transition before transforming to a third, high-pressure phase. The symmetry of this phase is revised to the centrosymmetric space group P21/c, resulting in the suppression of ferroelectricity at high pressure.

Glycine zinc sulfate penta-hydrate: redetermination at 10 K from time-of-flight neutron Laue diffraction.

Single crystals of glycine zinc sulfate penta-hydrate [systematic name: hexa-aqua-zinc tetra-aquadiglycinezinc bis-(sulfate)], [Zn(H2O)6][Zn(C2H5NO2)2(H2O)4](SO4)2, have been grown by isothermal evaporation from aqueous solution at room temperature and characterized by single-crystal neutron diffraction. The unit cell contains two unique ZnO6 octa-hedra on sites of symmetry -1 and two SO4 tetra-hedra with site symmetry 1; the octa-hedra comprise one [tetra-aqua-diglycine zinc]2+ ion (centred on one Zn atom) and one [hexa-aqua-zinc]2+ ion (centred on the other Zn atom); the glycine zwitterion, NH3+CH2COO-, adopts a monodentate coordination to the first Zn atom. All other atoms sit on general positions of site symmetry 1. Glycine forms centrosymmetric closed cyclic dimers due to N-H⋯O hydrogen bonds between the amine and carboxyl-ate groups of adjacent zwitterions and exhibits torsion angles varying from ideal planarity by no more than 1.2°, the smallest values for any known glycine zwitterion not otherwise constrained by a mirror plane. This work confirms the H-atom locations estimated in three earlier single-crystal X-ray diffraction studies with the addition of independently refined fractional coordinates and Uij parameters, which provide accurate inter-nuclear X-H (X = N, O) bond lengths and consequently a more accurate and precise depiction of the hydrogen-bond framework.

Use of a miniature diamond-anvil cell in high-pressure single-crystal neutron Laue diffraction.

The first high-pressure neutron diffraction study in a miniature diamond-anvil cell of a single crystal of size typical for X-ray diffraction is reported. This is made possible by modern Laue diffraction using a large solid-angle image-plate detector. An unexpected finding is that even reflections whose diffracted beams pass through the cell body are reliably observed, albeit with some attenuation. The cell body does limit the range of usable incident angles, but the crystallographic completeness for a high-symmetry unit cell is only slightly less than for a data collection without the cell. Data collections for two sizes of hexamine single crystals, with and without the pressure cell, and at 300 and 150 K, show that sample size and temperature are the most important factors that influence data quality. Despite the smaller crystal size and dominant parasitic scattering from the diamond-anvil cell, the data collected allow a full anisotropic refinement of hexamine with bond lengths and angles that agree with literature data within experimental error. This technique is shown to be suitable for low-symmetry crystals, and in these cases the transmission of diffracted beams through the cell body results in much higher completeness values than are possible with X-rays. The way is now open for joint X-ray and neutron studies on the same sample under identical conditions.

Type II Bi1 - xWxO1.5 + 1.5x: a (3 + 3)-dimensional commensurate modulation that stabilizes the fast-ion conducting delta phase of bismuth oxide.

The Type II phase in the Bi1 - xWxO1.5 + 1.5x system is shown to have a (3 + 3)-dimensional modulated δ-Bi2O3-related structure, in which the modulation vector ℇ `locks in' to a commensurate value of 1/3. The structure was refined in a 3 × 3 × 3 supercell against single-crystal Laue neutron diffraction data. Ab initio calculations were used to test and optimize the local structure of the oxygen sublattice around a single mixed Bi/W site. The underlying crystal chemistry was shown to be essentially the same as for the recently refined (3 + 3)-dimensional modulated structure of Type II Bi1 - xNbxO1.5 + x (Ling et al., 2013), based on a transition from fluorite-type to pyrochlore-type via the appearance of W4O18 `tetrahedra of octahedra' and chains of corner-sharing WO6 octahedra along 〈110〉F directions. The full range of occupancies on this mixed Bi/W site give a hypothetical solid-solution range bounded by Bi23W4O46.5 (x = 0.148) and Bi22W5O48 (x = 0.185), consistent with previous reports and with our own synthetic and analytical results.

Neutron Laue diffraction study of the complex low-temperature magnetic behaviour of brownmillerite-type Ca2Fe2O5

The atomic and magnetic structure of brownmillerite Ca2Fe2O5has been refined against single-crystal neutron Laue diffraction data collected at 300, 100 and 10 K under zero-field and low-magnetic field (35 Oe = 35 × 103/4π A m−1) conditions. Ca2Fe2O5is a canted G-type antiferromagnet withPcm′n′ symmetry, the magnetic moments on Fe being directed approximately along the crystallographiccaxis at room temperature. The refinement results show clearly that this magnetic structure persists down toT= 10 K, despite a previous suggestion that an anomalous magnetic susceptibility enhancement observed in Ca2Fe2O5single crystals between 40 and 140 K might signify a reorientation of the antiferromagnetic easy axis fromctoabelow 40 K. Alternative explanations for this susceptibility anomaly are considered in terms of the evidence for partial or short-range loss of order in the anomalous regime, possibly due to the presence of multiple competing sublattice interactions.

Structural Study of the Apatite Nd8Sr2Si6O26 by Laue Neutron Diffraction and Single-Crystal Raman Spectroscopy

A single-crystal structure determination of Nd8Sr2Si6O26 apatite, a prototype intermediate-temperature electrolyte for solid oxide fuel cells grown by the floating-zone method, was completed using the combination of Laue neutron diffraction and Raman spectroscopy. While neutron diffraction was in good agreement with P6₃/m symmetry, the possibility of P6₃ could not be convincingly excluded. This ambiguity was removed by the collection of orientation-dependent Raman spectra that could only be consistent with P6₃/m. The composition of Nd8Sr2Si6O26 was independently verified by powder X-ray diffraction in combination with electron probe microanalysis, with the latter confirming a homogeneous distribution of Sr and the absence of chemical zonation commonly observed in apatites. This comprehensive crystallochemical description of Nd8Sr2Si6O26 provides a baseline to quantify the efficacy of cation vacancies, oxygen superstoichiometry, and symmetry modification for promoting oxygen-ion mobility.

Surveying the higher dimensions of the aperiodic composite nonadecane/urea

We recently observed for the first time that there exist phase transitions where the structural changes correspond just to degrees of freedom hidden in the internal (super)space of an aperiodic material, here the composite nonadecane/urea [1]. A key factor in the discovery of this type of transition [2] was the examination of the diffraction pattern in 3D, only possible at the time on a four-circle triple-axis neutron spectrometer, the analyzer used in zero-energy transfer to reduce the background and improve resolution. Despite the greater accessibility in reciprocal space, the weak intensity of the superlattice reflections limited the volume of reciprocal space that could be explored. Modern neutron Laue diffractometers with large image-plate detectors permit rapid and extensive exploration of reciprocal space with high resolution in the two-dimensional projection and a wide dynamic range with negligible bleeding of intense diffraction spots [3]. Surveying nonadecane/urea with neutron Laue diffraction from 300K to 4K reveals further detail of the superspace-driven phase transition, notably an increase in misorientation in the plane perpendicular to the composite misfit axis, as well as a first-order transition to a new phase at lower temperature. These new observations shed further light on how nature can use the degrees of freedom hidden in the internal superspace to form states that cannot be envisaged in the usual 3D real space.

Low-T magnetic anomaly in Ca2Fe2O5studied by single-crystal neutron diffraction

Ca2Fe2O5, which belongs to the Brownmillerite family of promising solid-oxide fuel cell membrane materials, is an antiferromagnet (AFM) below TN = 720 K. A small ferromagnetic (FM) canting perpendicular to the AFM easy axis has previously been established by physical properties measurements, but never observed crystallographically. More intriguingly, it has been known for some time to display an anomalous elevation in magnetic susceptibility for 60 K < T < 140 K. [1] Based on measurements performed with small oriented single crystals, Zhou et al. [2] proposed that this anomaly was due to a reorientation of the spins from the crystallographic a axis to the c axis below 40 K, with a region of minimal magnetocrystalline anisotropy in the anomalous temperature interval. In order to test this, we grew a very large (~1 cm3) single crystal by the floating-zone method and collected neutron Laue diffraction data, against which we refined both the atomic and magnetic structures of Ca2Fe2O5 between 10 K and 300 K. We designed and built an ad hoc sample mount to apply a small (~35 Oe) magnetic field to the sample, ensuring perfect consistency with the magnetic susceptibility data, which were collected in a comparably small field. Our refinements against both zero-field and in-field diffraction data reproduce the G-type AFM structure of Ca2Fe2O5 excellently at room temperature, including the FM canting which we have refined to statistical significance for the first time. We can also show that in the intermediate temperature interval (T = 100 K), the spins are slightly less well-ordered due to competing sublattice interactions. However, careful examination of the data reveals that the material is still best described by the room-temperature magnetic structure at all measured temperatures – i.e., the spin-reorientation hypothesis is incorrect.

Neutron and X-ray Diffraction from Exotic Magnets in Pulsed Magnetic Fields

Magnetic fields obtained by discharging a large capacitor bank through Helmholtz coils can be produced in excess of 25 T for relatively short periods of time, ~ 1 msec and longer. When combined with modern facilities for diffraction at modern neutron and synchrotron x-ray sources, one can study the structure and phase diagrams of new materials under extremes of magnetic field. I will present two such studies, each focussing on a new magnetic material which exhibit exotic low temperature states. I will show time-resolved neutron Laue diffraction on the multiferroic magnet MnWO4 [1], and time-resolved synchrotron x-ray studies of large magneto-elastic effects in the geometrically-frustarted pyrochlore magnet Tb2Ti2O7 [2], both in magnetic fields up to ~ 30 T. Such studies of new materials in extreme sample environments can be very revealing as to the nature of their exotic low temperature states.