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The sodium tungsten bronzes are nonstoichiometric metal oxides which have recently attracted interest for their applications as plasmonic materials. Although several synthesis routes have been repo...

Metastable austenite strongly influences the mechanical properties of many advanced high strength steels (AHSS) and its formation kinetics during intercritical annealing strongly depend on the initial microstructure. In this contribution, we have performed detailed kinetic studies of austenite formation from cementite-ferrite aggregate in a range of Fe-C-Mn and Fe-C-Mn-Si/Al alloys via in situ neutron powder diffraction. Depending on the relative contribution of cementite dissolution in respect to migrating interface of austenite/ferrite, the incomplete dissolution of enveloped cementite limited by slow diffusion in austenite could result in austenite plateauing below equilibrium, while fast dissolution of matrix cementite could result in austenite plateau above equilibrium. Both contributions need to be considered and modelled to describe the austenite formation kinetics.

The influence of molecular confinement on the melting transition of oriented Na-DNA fibers submerged in poly(ethylene glycol) (PEG) solutions has been studied. The PEG solution exerts an osmotic pressure on the fibers which, in turn, is related to the DNA intermolecular distance. Calorimetry measurements show that the melting temperature increases and the width of the transition decreases with decreasing intermolecular distance. Neutron scattering was used to monitor the integrated intensity and width of a Bragg peak from the B-form of DNA as a function of temperature. The data were quantitatively analyzed using the Peyrard-Bishop-Dauxois model. The experiments and analysis showed that long segments of double-stranded DNA persist until the last stages of melting and that there appears to be a substantial increase of the DNA dynamics as the melting temperature of the DNA is approached.

The reduction of New Zealand titanomagnetite ironsand in a dilute hydrogen–nitrogen gas mixture was studied in situ using neutron diffraction. Neutron diffraction allowed in situ observation of lar...

Through the detailed studies utilizing x-ray and neutron powder diffraction and magnetometry measurements, we report the magnetic phase transitions in the B-site disorder perovskite oxide PrFe0.5Cr0.5O3. The Fe3+/Cr3+ sublattice was observed to form a long-range magnetic order with the GxFz configuration below TN = 270 K from neutron powder diffraction. It then undergoes the second-order phase transition to FxGz spin configuration below 210 K and the transition ends at ~170 K. On the other hand, long range magnetic ordering with FxCy configuration at Pr3+ sublattice can be identified at base temperature. The magnetic phase diagram is derived with spontaneous spin ordering and reorientation at A- and B-sublattices.

We detected a crossover from negative to positive thermal expansion with increasing Mn in HoCo2Mnx below the Curie temperature through high quality neutron diffraction measurements from 5 K to 400 K. Almost isotropic zero thermal expansion with coefficient of thermal expansion αl = −4.894 × 10−7/K was achieved over a large range of temperature from 5 K to TC = 225 K in the compound HoCo2Mn0.5. While the addition of manganese was shown to change the temperature dependence of the lattice, it was also noted that the Curie temperature rose significantly from 88 K in HoCo2 to 253 K in HoCo2Mn providing a hope for a room temperature transition in similar doping series materials.

The mechanical flexibility of coordination frameworks can lead to a range of highly anomalous structural behaviours. Here, we demonstrate the extreme compressibility of the LnFe(CN)6 frameworks (Ln = Ho, Lu or Y), which reversibly compress by 20% in volume under the relatively low pressure of 1 GPa, one of the largest known pressure responses for any crystalline material. We delineate in detail the mechanism for this high compressibility, where the LnN6 units act like torsion springs synchronized by rigid Fe(CN)6 units performing the role of gears. The materials also show significant negative linear compressibility via a cam-like effect. The torsional mechanism is fundamentally distinct from the deformation mechanisms prevalent in other flexible solids and relies on competition between locally unstable metal coordination geometries and the constraints of the framework connectivity, a discovery that has implications for the strategic design of new materials with exceptional mechanical properties.

The MPS3 family of layered magnetic materials (M = Fe2+, Ni2+, Mn2+, etc) shows many unusual properties. We have recently observed time-dependent magnetisation and two magnetic phase transitions in Fe0.5Ni0.5PS3, and here we use neutron diffraction and Mossbauer spectroscopy to explore the magnetic and structural ordering. Neutron diffraction shows that the staggered magnetisation lies closest to the Brillouin curve for J = 1, which is the spin for quenched Ni2+. In agreement with neutron diffraction, Mossbauer spectroscopy shows a magnetic ordering temperature of ∼120K. It does not show any evidence of a second, low temperature (re)ordering, suggesting that the low temperature transition seen previously is a result of the time dependence of the magnetisation and is not apparent when the sample is given time to relax between measurements. The presence of three magnetic Fe-site environments when four chemical environments (Fe3, Fe2Ni, FeNi2 and Ni3) are possible may indicate that the mixture is not random, but shows some local ordering; the neutron results show evidence for a similar conclusion.

The formation and decomposition of silico-ferrite of calcium and aluminium (SFCA) and SFCA-I iron ore sinter bonding phases have been investigated usingin situsynchrotron and laboratory X-ray diffraction (XRD) and neutron diffraction (ND). An external standard approach for determining absolute phase concentrations via Rietveld refinement-based quantitative phase analysis is discussed. The complementarity ofin situXRD and ND in characterising sinter phase formation and decomposition is also shown, with the volume diffraction afforded by the neutron technique reducing errors in the quantification of magnetite above ~1200 °C. Finally, by collecting 6 s laboratory XRD datasets and using a heating rate of 175 °C min−1, phase formation and decomposition have been monitored under heating rates more closely approximating those encountered in industrial iron ore sintering.

Effects of basicity, B (CaO:SiO2 ratio) on the thermal range, concentration, and formation mechanisms of silico-ferrite of calcium and aluminum (SFCA) and SFCA-I iron ore sinter bonding phases have been investigated using an in situ synchrotron X-ray diffraction-based methodology with subsequent Rietveld refinement-based quantitative phase analysis. SFCA and SFCA-I phases are the key bonding materials in iron ore sinter, and improved understanding of the effects of processing parameters such as basicity on their formation and decomposition may assist in improving efficiency of industrial iron ore sintering operations. Increasing basicity significantly increased the thermal range of SFCA-I, from 1363 K to 1533 K (1090 °C to 1260 °C) for a mixture with B = 2.48, to ~1339 K to 1535 K (1066 °C to 1262 °C) for a mixture with B = 3.96, and to ~1323 K to 1593 K (1050 °C to 1320 °C) at B = 4.94. Increasing basicity also increased the amount of SFCA-I formed, from 18 wt pct for the mixture with B = 2.48 to 25 wt pct for the B = 4.94 mixture. Higher basicity of the starting sinter mixture will, therefore, increase the amount of SFCA-I, considered to be more desirable of the two phases. Basicity did not appear to significantly influence the formation mechanism of SFCA-I. It did, however, affect the formation mechanism of SFCA, with the decomposition of SFCA-I coinciding with the formation of a significant amount of additional SFCA in the B = 2.48 and 3.96 mixtures but only a minor amount in the highest basicity mixture. In situ neutron diffraction enabled characterization of the behavior of magnetite after melting of SFCA produced a magnetite plus melt phase assemblage.

This work presents a detailed microstructure and texture study of various hydrided Zircaloy-4 materials by neutron diffraction and microscopy. The results show that the precipitated δ-ZrH1.66 generally follows the δ (111) //α (0001) and δ[]//α[] orientation relationship with the α-Zr matrix. The δ-hydride displays a weak texture that is determined by the texture of the α-Zr matrix, and this dependence essentially originates from the observed orientation correlation between α-Zr and δ-hydride. Neutron diffraction line profile analysis and high-resolution transmission electron microscopy observations reveal a significant number of dislocations present in the δ-hydride, with an estimated average density one order of magnitude higher than that in the α-Zr matrix, which contributes to the accommodation of the substantial misfit strains associated with hydride precipitation in the α-Zr matrix. The present observations provide an insight into the behaviour of δ-hydride precipitation in zirconium alloys and may help with understanding the induced embrittling effect of hydrides. Fil: Wang, Zhiyang. University of Wollongong; Australia. Australian Nuclear Science and Technology Organisation; Australia Fil: Garbe, Ulf. Australian Nuclear Science and Technology Organisation; Australia Fil: Li, Huijun. University of Wollongong; Australia Fil: Wang, Yanbo. University of Sydney; Australia Fil: Studer, Andrew J.. Australian Nuclear Science and Technology Organisation; Australia Fil: Sun, Guangai. Institute of Nuclear Physics and Chemistry, CAEP; China Fil: Harrison, Robert P.. Australian Nuclear Science and Technology Organisation, Institute of Materials Engineering; Australia Fil: Liao, Xiaozhou. University of Sydney; Australia Fil: Vicente Alvarez, Miguel Angel. Comisión Nacional de Energía Atómica. Gerencia del Área de Energía Nuclear. Instituto Balseiro; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina Fil: Santisteban, Javier Roberto. Comisión Nacional de Energía Atómica. Gerencia del Área de Energía Nuclear. Instituto Balseiro; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina Fil: Kong, Charlie. University of New South Wales; Australia

The hydride formation and its influence on the mechanical performance of hydrided Zircaloy-4 plates containing different hydrogen contents were studied at room temperature. For the unnotched plate samples with the hydrogen contents ranging from 25 to 850 wt. ppm, the hydrides exerted an insignificant effect on the tensile strength, while the ductility was severely degraded with increasing hydrogen content. The fracture mode and degree of embrittlement were strongly related to the hydrogen content. When the hydrogen content reached a level of 850 wt. ppm, the plate exhibited negligible ductility, resulting in almost completely brittle behavior. For the hydrided notched plate, the tensile stress concentration associated with the notch tip facilitated the hydride accumulation at the region near the notch tip and the premature crack propagation through the hydride fracture during hydriding. The final brittle through-thickness failure for this notched sample was mainly attributed to the formation of a continuous hydride network on the thickness section and the obtained very high hydrogen concentration (estimated to be 1965 wt. ppm).

The gaseous hydriding-induced evolutions of the microstructure, texture and mechanical properties of Zircaloy-4 processed by high-pressure torsion (HPT) were assessed. Much δ-ZrH1.66 precipitation at 15 atm (21%) incurred significant hardening of vacuum-annealed HPT samples, and pure e-ZrH2 obtained at 20 atm showed a superior microhardness of 470 HV0.3 and a low fracture toughness of 0.63 MPa m1/2. The δ-hydrides presented strong (1 1 1) texture and followed the (0 0 0 1)α-Zr//{1 1 1}δ-ZrH1.66 orientation relationship with the α-Zr matrix. During hydriding, α-Zr recrystallization texture was developed from the initial deformation texture.

Using sol–gel synthesis, single phase perovskite-related compounds in the family La 1 − x Ca x FeO 3 − δ have been formed for x=0.2 and x=0.33, but not for x=0.5. The x=0.2 and x=0.33 compounds are isostructural with LaFeO 3 (Pnma). The magnetic structure of La 0.8 Ca 0.2 FeO 3 − δ has been studied through Mossbauer spectroscopy and neutron powder diffraction. La 0.8 Ca 0.2 FeO 3 − δ is a G-type antiferromagnet with a magnetic moment magnitude of 3.0 ± 0.2 μ B at room temperature. The reduction in the magnitude of the antiferromagnetic moment compared to that published for LaFeO 3 is explained by the measurement being taken at room temperature rather than 4 K and by the presence of Fe 4 + ions which have weaker exchange interactions than Fe 3 + , causing a strong reduction in TN. Room temperature Mossbauer shows a broad magnetic hyperfine field distribution on the Fe sites in both La 0.8 Ca 0.2 FeO 3 − δ and La 0.67 Ca 0.33 FeO 3 − δ . On cooling, disproportionation of Fe 4 + into Fe 3 + and Fe5+ is apparent, and the resulting Fe5+ sextet measured at low temperature gives a reliable measure of the Fe 4 + fraction. This in turn shows that creation of high-oxidation-state Fe is the dominant charge balance mechanism on doping Ca 2 + into the Ln 3 + site indicating a disordered distribution of Fe 3 + and Fe 4 + . The lack of broadening of the Fe5+ sextet suggests that there may be ordering in the distribution of Fe5+.

The influence of temperature on the kinetics of domain switching in lead zirconate titanate was investigated by using in situ neutron diffraction. Samples were electrically loaded to 1 kV/mm at 30°C, 125°C, and 175°C, after which the diffracted patterns in the on- and off-state were compared. The results demonstrated that the degree of domain switching increases with increased temperature. Corroboration with hysteresis measurements showed that while the coercive field decreases with increasing temperature, the degree of saturation increased significantly. According to Merz's model, it is therefore apparent that, due to increased switching rate at high temperature, domain switchability increases with temperature.

The thermal stability of Ti2AlC at elevated temperature (1000–1550 °C) in vacuum has been investigated using in situ neutron diffraction. At temperatures above 1400 °C, Ti2AlC became unstable and began to decompose via sublimation of Al, resulting in a porous surface layer of TiCx being formed. The apparent activation energy for Ti2AlC decomposition was determined to be 85.7 ± 2.6 kJ mol−1. The kinetics of isothermal phase decomposition was modelled using least-squares linear regression fitting and the Avrami equation. The corresponding least-squares regression exponent (R2) and Avrami constants (k and n) for isothermal decomposition were determined to be 0.89, 0.268 min−n and 0.1, respectively.

The structural response to electrochemical cycling of the components within a commercial Li-ion battery (LiCoO2 cathode, graphite anode) is shown through in situ neutron diffraction. Lithuim insertion and extraction is observed in both the cathode and anode. In particular, reversible Li incorporation into both layered and spinel-type LiCoO2 phases that comprise the cathode is shown and each of these components features several phase transitions attributed to Li content and correlated with the state-of-charge of the battery. At the anode, a constant cell voltage correlates with a stable lithiated graphite phase. Transformation to de-lithiated graphite at the discharged state is characterised by a sharp decrease in both structural cell parameters and cell voltage. In the charged state, a two-phase region exists and is composed of the lithiated graphite phase and about 64% LiC6. It is postulated that trapping Li in the solid|electrolyte interface layer results in minimal structural changes to the lithiated graphite anode across the constant cell voltage regions of the electrochemical cycle.

We have observed the effects of phonon mode softening at the ferroelectric transition in Eu0.5Ba0.5TiO3 by 151 Eu Mossbauer spectroscopy. Both Eu 2+ and Eu 3+ spectral components are observed in the relative area ratio of 90% : 10% and both show a decrease in subspectral area at the transition, centred at 175 K, due to phonon mode softening. Surprisingly, the temperature dependence of the f-factor shows a much stronger response in the Eu 3+ component than in the Eu 2+ one. Preliminary analysis of neutron powder diffraction data rules out the possibility that some of the europium might be located on titanium sites.

Structural changes in commercial lead zirconate titanate (PZT) ceramics (EC-65) under the application of electric fields and mechanical stress were measured using neutron diffraction instruments at the Australian Nuclear Science and Technology Organisation (ANSTO) and the Oak Ridge National Laboratory (ORNL). The structural changes during electric-field application were measured on the WOMBAT beamline at ANSTO and include non-180° domain switching, lattice strains and field-induced phase transformations. Using time-resolved data acquisition capabilities, lattice strains were measured under cyclic electric fields at times as short as 30 μs. Structural changes including the (002) and (200) lattice strains and non-180° domain switching were measured during uniaxial mechanical compression on the NRSF2 instrument at ORNL. Contraction of the crystallographic polarization axis, (002), and reorientation of non-180° domains occur at lowest stresses, followed by (200) elastic strains at higher stresses.

The influence of the frequency and amplitude of cyclic mechanical loading on soft, tetragonal lead zirconate titanate (PZT) ceramics was investigated via neutron diffraction. Intensity change in the {2 0 0} reflections provided quantitative measurements of domain switching behavior, domain texture and the strain resulting from domain switching. The results are explained using a viscoelasticity model. It was found that the magnitude of applied stress affects the level of strain accumulated, while its frequency affects the time taken for the strain to reach saturation. Furthermore, markedly different behaviors are exhibited by poled and unpoled samples. For samples loaded under identical conditions, the frequency effect is more pronounced in unpoled samples and the accumulated ferroelastic strain is greater in poled samples.

International audience; A pilot study of the possibility to investigate temperature-dependent neutron scattering from fiber-DNA in solution is presented. The study aims to establish the feasibility of experiments to probe the influence of spatial confinement on the structural correlation and the formation of denatured bubbles in DNA during the melting transition. Calorimetry and neutron scattering experiments on fiber samples immersed in solutions of poly(ethylene glycol) (PEG) prove that the melting transition occurs in these samples, that the transition is reversible to some degree, and that the transition is broader in temperature than for humidified fiber samples. The PEG solutions apply an osmotic pressure that maintains the fiber orientation, establishing the feasibility of future scattering experiments to study the melting transition in these samples

We have investigated the magnetic behaviour of PrMn2−xFexGe2 compounds with x = 0.4, 0.6 and 0.8 over the temperature range 4.2–350 K using ac magnetic susceptibility, dc magnetization and 57Fe Mossbauer effect spectroscopy, as well as neutron diffraction for the PrMn1.2Fe0.8Ge2 compound. Replacement of Mn with Fe leads to contraction of the unit cell and a shortening of the Mn–Mn spacing, resulting in modification of the magnetic structure. PrMn1.6Fe0.4Ge2 is an intralayer antiferromagnet at room temperature and ferromagnetic below TCinter~230 K with additional ferromagnetic ordering of the Pr sublattice detected below TCPr~30 K. Re-entrant ferromagnetism has been observed in PrMn1.4Fe0.6Ge2 with four magnetic transitions (TNintra~333 K, TCinter~168 K, TNinter~152 K and TCPr~40 K). Moreover, it was found that TCinter and TCPr increase with applied field while TNinter decreases. PrMn1.2Fe0.8Ge2 is antiferromagnetic with TNintra~242 K and TNinter~154 K. The magnetic transition temperatures for all compounds are also marked by changes in the 57Fe magnetic hyperfine field and the electric quadrupole interaction parameters. The 57Fe transferred hyperfine field at 4.5 K in PrMn1.6Fe0.4Ge2 and PrMn1.4Fe0.6Ge2 is reduced (below the ordering temperature of the Pr sublattice) compared with that at 80 K (above TCPr), indicating that the transferred hyperfine field from Pr acts in the opposite direction to that from the Mn atoms. The neutron data for PrMn1.2Fe0.8Ge2 demonstrate that an anisotropic thermal expansion occurs within the interplanar antiferromagnetic range.

The kinetics of the exsolution of pentlandite from the monosulfide solid solution (mss) have been investigated using a series of anneal/quench and in situ cooling neutron diffraction experiments. Five mss compositions were examined by anneal/quench techniques covering the composition range Fe 0 . 9 Ni 0 . 1 S to Fe 0 . 6 5 Ni 0 . 3 5 S and using annealing temperatures between 423 and 773 K for periods from 1 h to 5 months. In situ cooling experiments were performed on four mss compositions in the range Fe 0 . 9 Ni 0 . 1 S to Fe 0 . 7 Ni 0 . 3 S. The samples of these solid solutions were heated to 973 K, and then cooled to 373 K in steps of 50 K over a 24 h period. The extent of exsolution was monitored by Rietveld phase analysis using powder neutron diffraction data. The anneal/quench experiments established that initial exsolution of pentlandite from mss above 573 K is very rapid and is effectively complete within 1 h of annealing. However, the mss/pyrrhotite compositions remained Ni rich (17 at% Ni) after 5 months annealing, indicating that compositional readjustment at low-temperatures occurs over long periods. Below 573 K, exsolution is less rapid with rate constants in the range 6 x 10 - 6 to 1 x 10 - 5 /s and the activation energy for exsolution of pentlandite from mss Fe 0 . 8 Ni 0 . 2 S between 473 and 423 K is 5 kJ/mol. The in situ cooling experiments showed that the temperature at which exsolution commences upon cooling decreases from 873 K for Fe 0 . 7 Ni 0 . 3 S to 823 K for Fe 0 . 9 Ni 0 . 1 S and that exsolution effectively ceased on the time scale of the experiments at temperatures between 598 and 548 K. The kinetic data were analyzed using the Avrami model where y = 1 - exp(-k n t n ) and the initial rates of exsolution were found to increase with Ni content from 2 x 10 - 6 /s for Fe 0 . 9 Ni 0 . 1 S to 4 x 10 - 5 /s for Fe 0 . 7 Ni 0 . 3 S. Both high Ni content and high M:S ratio served to facilitate nucleation rate, indicating that nucleation occurs at S vacancies within mss crystals rather than at grain boundaries. Values of the Avrami geometric constant n vary during exsolution upon cooling indicating three possible changes in the growth mechanism during the reaction. The roles of impurities and S fugacity on reaction rates are discussed. The rate constants for exsolution of pentlandite from mss/pyrrhotite in nature are estimated to be 4 or 5 orders of magnitude slower than those reported here, still very rapid on a geological time scale. High metal mobility persists in this system at low temperatures, even at room temperature, and the textures and compositions observed in nature are a consequence of very low-temperature (

Variations in the structure of gamma-alumina (γ-Al2O3), derived from well-crystalline boehmite, calcined at various temperatures in air were investigated. Consistent distribution of cation coordina...

A novel quadruple perovskite oxide CeCu3Fe4O12 has been synthesized under high-pressure and high-temperature conditions of 15 GPa and 1473 K. (57)Fe Mössbauer spectroscopy displays a charge disproportionation transition of 4Fe(3.5+) → 3Fe(3+) + Fe(5+) below ∼270 K, whereas hard X-ray photoemission and soft X-ray absorption spectroscopy measurements confirm that the Ce and Cu valences are retained at approximately +4 and +2, respectively, over the entire temperature range measured. Electron and X-ray diffraction studies reveal that the body-centered cubic symmetry (space group Im3̅, No. 204) is retained at temperatures as low as 100 K, indicating the absence of any types of charge-ordering in the charge-disproportionated CeCu3Fe4O12 phase. The magnetic susceptibility and neutron powder diffraction data illustrate that the antiferromagnetic ordering of Fe ions is predominant in the charge-disproportionated CeCu3Fe4O12 phase. These findings suggest that CeCu3Fe4O12 undergoes a new type of electronic phase in the ACu3Fe4O12 series and that the melting of the charge-ordering in CeCu3Fe4O12 is caused by the substantial decrease in the Fe valence and the resulting large deviation from the ideal abundance ratio of Fe(3+):Fe(5+) = 1:1 for rock-salt-type charge-ordering.

Ferroelastic domain switching during dynamic actuation is measured in situ for a piezoelectric lead zirconate titanate (PZT) ceramic utilizing a new capability developed on The Australian Strain Scanner (TASS) at ANSTO. Diffraction patterns are obtained as a function of time during a 1 Hz cycle. The change in the 0 0 2 and 2 0 0 diffraction intensities indicates there is ferroelastic domain switching at sub-coercive (weak) fields.

An experimental facility to measure the time dependence of neutron Bragg peak intensities, in response to applied high-voltage electric fields is described. The stroboscopic technique with a timing resolution below 20 μs has been applied to study crystals of tryglycine sulphate near its ferroelectric transition temperature and in this paper data are presented showing the response of the (0 6 0) reflection to an applied field square wave at 1 kHz for various temperatures.

We report the dramatic effect of applied pressure and magnetic field on the layered intermetallic compound Pr(0.5)Y(0.5)Mn(2)Ge(2). In the absence of pressure or magnetic field this compound displays interplanar ferromagnetism at room temperature and undergoes an isostructural first order magnetic transition (FOMT) to an antiferromagnetic state below 158 K, followed by another FOMT at 50 K due to the reemergence of ferromagnetism as praseodymium orders (T(C)(Pr)). The application of a magnetic field drives these two transitions towards each other, whereas the application of pressure drives them apart. Pressure also produces a giant magnetocaloric effect such that a threefold increase of the entropy change associated with the lower FOMT (at T(C)(Pr)) is seen under a pressure of 7.5 kbar. First principles calculations, using density functional theory, show that this remarkable magnetic behavior derives from the strong magnetoelastic coupling of the manganese layers in this compound.

We report a detailed study of the dynamics of oxide ionic conduction in brownmillerite-type Sr2Fe2O5, including lat-tice anisotropy, based on neutron scattering studies of a large (partially twinned) single crystal in combination with ab initio molecular dynamics simulations. Single-crystal diffraction reveals supercell peaks due to long-range order-ing among chains of corner-sharing FeO4 tetrahedra, which disappears on heating above 540 °C due to confined local rotations of tetrahedra. Our simulations show that these rotations are essentially isotropic, but are a precondition for the anisotropic motion that moves oxide ions into the tet-rahedral layers from the octahedral layers, which we observe experimentally as a Lorentzian broadening of the quasielas-tic neutron scattering spectrum. This continual but incoher-ent movement of oxide ions in turn creates conduction pathways and activates long-range diffusion at the interface between layers, which appears to be largely isotropic in two dimensions, in contrast with previously proposed mecha-nisms that suggest diffusion occurs preferentially along the c axis.

The crystal and magnetic structures of the bilayer manganites PrSr2Mn2O7 (PSMO) and PrCa2Mn2O7 (PCMO) have been studied by neutron powder diffraction. It was found that PSMO crystallizes in space group I4/mmm, while PCMO adopts space group Cmc21 at room temperature. The difference in the structure arises from chemical pressure induced by the Ca substitution for Sr on the A sites, which causes different Jahn-Teller distortions. In PSMO, the MnO6 octahedra suffer a small elongated distortion, while those in PCMO adopt strong compressed distortion along the axial direction. In addition, the octahedra in PCMO show a+b0c0 rotation and a0b+c+ tilting in the Glazer notation in comparison to PSMO. As a result, these two compounds adopt very different magnetic structures: The magnetic structure of PSMO is an A-type magnetic structure (Im'm'm) with propagation vector k = (0, 0, 1) and magnetic moments in the ab plane. In contrast, a C-type antiferromagnetic magnetic structure (Cm'c2′1) with the multiple propagation...

Large refrigeration capacities, between 212(30) J kg−1 and 261(40) J kg−1 for a magnetic field change from 0 T to 5 T, were obtained in Mn1−x Fe x CoGe (x = 0.01, 0.02, 0.03 and 0.04) compounds. A partial magnetic phase diagram has been derived on the basis of magnetic transition and martensitic transformation temperatures determined from differential scanning calorimetry (200 K to 450 K), variable temperature x-ray diffraction (20 K to 310 K) and magnetisation measurements (5 K to 340 K; 0.01 T). Mn1−x Fe x CoGe compounds with compositions in the range x = 0.01 to 0.03 exhibit magneto-structural transitions. Neutron diffraction experiments were carried out on the Mn0.98Fe0.02CoGe sample over the temperature range of 5 K to 450 K. The diffraction patterns were analysed based on irreducible representation theory which confirms a ferromagnetic structure in the sample with an atomic magnetic moment of 3.7(1)μ B at 5 K on the Mn sublattice, oriented along the orthorhombic c axis. More significantly, a magneto-structural transition around T M ~ 297(1) K with a full width at half maximum of 29 K is demonstrated directly via neutron diffraction. Larger magnetic entropy changes are obtained for the Mn1−x Fe x CoGe (x = 0.01, 0.02 and 0.03) samples than for Mn0.96Fe0.04CoGe which has separate structural and magnetic transitions. In addition, it is noted that standard Arrott plots do not provide unambiguous insight to the nature of the magneto-structural transition in the Mn1−x Fe x CoGe compounds.

Neutron diffraction, magnetization, resistivity, and heat-capacity measurements on the 6H-perovskite Ba${}_{3}$BiRu${}_{2}$O${}_{9}$ reveal simultaneous magnetic and structural dimerization driven by strong magnetoelastic coupling. An isostructural but strongly displacive first-order transition on cooling through ${T}^{*}=176$ K is associated with a change in the nature of direct Ru--Ru bonds within Ru${}_{2}$O${}_{9}$ face-sharing octahedra. Above ${T}^{*}$, Ba${}_{3}$BiRu${}_{2}$O${}_{9}$ is an $S=1$ magnetic dimer system with intradimer exchange interactions ${J}_{0}/{k}_{\mathrm{B}}=320$ K and interdimer exchange interactions ${J}^{\ensuremath{'}}/{k}_{\mathrm{B}}=\ensuremath{-}160$ K. Below ${T}^{*}$, a spin-gapped state emerges with $\ensuremath{\Delta}\ensuremath{\approx}220$ K. Ab initio calculations confirm antiferromagnetic exchange within dimers, but the transition is not accompanied by long-range magnetic order.

The novel quaternary rare-earth transition-metal intermetallic compound Nd3Ni29Si4B10 of space group P4/nmm (No. 129) has been synthesised and its structure determined. The crystal structure has been investigated by scanning electron microscopy, X-ray and neutron powder diffraction measurements. Rietveld refinements of the powder X-ray and neutron diffraction patterns reveal a tetragonal structure of lattice parameters a=b=11.2327(7) A, c=7.8754(3) A with two formula units of Nd3Ni29Si4B10 per unit cell. The structure contains two rare-earth crystallographic sites of high symmetry, four B sites, seven transition metal sites and one Si site. The Ni atoms at the 2c 4 mm crystallographic site have a quasi-spherical polyhedral coordination.

The thermal expansion coefficients for natural troilite, FeS, Ni-rich pyrrhotite, Fe0.84Ni0.11S, and Ni-poor pyrrhotite, Fe0.87Ni0.02S, were measured during cooling by in situ neutron powder diffraction over the temperature range 873–373 K. Between 873 and 573 K, the mean thermal expansion coefficients for the three compositions are 7.4(3)×10−5{FeS}, 8.0(4)×10−5{Fe0.84Ni0.11S} and 8.5(4)×10−5K−1{Fe0.87Ni0.02S}. Below 573 down to 373 K, the first two increase considerably to 14.1(7)×10−5{FeS} and 9.3(5)×10−5{Fe0.84Ni0.11S} while the latter sample shows no significant variation, 8.4(5)×10−5K−1. Below 573 K, the thermal expansion is highly anisotropic, with Δa/100 K−1ranging from 0.89(9)% {FeS} to 0.48(12)% {Fe0.87Ni0.02S} while Δc/100 K−1ranges from −0.39(11)% {FeS} to −0.13(2)% {Fe0.87Ni0.02S}.Upon cooling through 573 K, troilite and pyrrhotite undergo a transition where the FeS6octahedra distort and in the case of pyrrhotite, cation-vacancy clustering occurs. The thermal expansion coefficients are bigger for low cation-vacancy concentrations and decrease as the pyrrhotites become less stoichiometric. This indicates that the thermal expansion in these minerals is damped by vacancy ordering or clustering. The thermal expansion coefficients for troilite and pyrrhotite are amongst the largest reported for sulphide minerals and their role in the formation of ore textures is discussed briefly.

We show that large single crystals of brownmillerite-type Ca2Fe2O5 can be grown using the floating-zone method under ambient pressure conditions, provided that the feed rods are pre-annealed to a very high density. Neutron diffraction data collected from these crystals show the emergence of a long-range ordered incommensurate phase at high temperature. The observation of this phase for the first time using neutrons proves that the incommensurate ordering of tetrahedral chains upon heating Ca2Fe2O5 is a truly long-range and bulk phenomenon. The results are used to compare and contrast the structures of Ca2Fe2O5 and Sr2Fe2O5, and are consistent with experimental observations of significantly higher oxide ionic conduction in the latter material.

The contribution of non-180° domain wall displacement to the frequency dependence of the longitudinal piezoelectric coefficient has been determined experimentally in lead zirconate titanate using time-resolved, in situ neutron diffraction. Under subcoercive electric fields of low frequencies, approximately 3% to 4% of the volume fraction of non-180° domains parallel to the field experienced polarization reorientation. This subtle non-180° domain wall motion directly contributes to 64% to 75% of the magnitude of the piezoelectric coefficient. Moreover, part of the 33 pm/V decrease in piezoelectric coefficient across 2 orders of magnitude in frequency is quantitatively attributed to non-180° domain wall motion effects.

Morphotropic phase boundary (MPB) containing piezoelectric systems generally exhibit enhanced piezoelectric performance at compositions within, or close to, the MPB region. The mechanism/s underlying such enhancement, however, are still contentious due to complex micro/nanostructure and apparently inherent local structural variability associated with octahedral tilt disorder/platelet precipitates in such piezoelectric materials. This paper reviews some recent structural analysis results from Bi0.5Na0.5TiO3 (BNT) and other binary, lead-free, piezoelectric materials systems derived from it via electron diffraction and in situ neutron diffraction. The results suggest that intrinsically existing local microstructure (LMS) in BNT essentially continues across the MPB region. The LMS, originating from inherent octahedral tilt disorder, is strongly temperature-, electric field-, pressure- and chemical composition-dependent, and may help to explain a series of phenomena observed in BNT-based binary materials systems, including the enhanced piezoelectric effect in the region of the MPB.

Here we report a detailed investigation of NdMn2Ge1.6Si0.4; this forms part of our investigation of the magnetic order across the NdMn2Ge2−xSix (x = 0–2.0) series by magnetometry, x-ray diffraction and neutron diffraction over the temperature range 6–465 K. On decreasing the temperature from 465 K, NdMn2Ge1.6Si0.4 exhibits four magnetic transitions: (i) from paramagnetism to intralayer antiferromagnetism AFl at TIntraN ~ 430 K; (ii) AFl to canted ferromagnetism Fmc at TInterC ~ 330 K; (iii) Fmc to conical magnetic ordering of the Mn sublattice Fmi at Tcc ~ 178 K and (iv) Fmi(Mn) to Fmi(Mn)+F(Nd) at TNdC ~ 72 K.

The structural and magnetic properties of Ho2Fe17−xMnx (x=0−5) have been investigated by x-ray diffraction, Mossbauer spectroscopy and DC magnetization measurements (0-5 T) over the temperature range 4.5–350 K. Similar to other ferrimagnetic R2Fe17−xMnx systems, the unit cell volume generally increases with Mn content other than for low Mn values where a slight maximum is detected around x ~ 0.5. The nature of the magnetic phase transitions around TC is shown by Arrot plot analysis to be second order for all samples. The Curie temperature remains essentially unchanged for Mn contents up to x=1.0 (TC = 336 K for x=0.0, TC = 338 K for x=1.0) before decreasing steadily with further increase in Mn content (TC = 209 K for x=5). The 57Fe hyperfine interaction parameters have been determined from variable temperature Mossbauer spectra.

The effects of replacing Pr by Lu on the magnetic behaviour and structures of Pr(1-x)Lu(x)Mn(2)Ge(2) (x = 0.2,x = 0.4) have been investigated using x-ray diffraction, Mössbauer spectroscopy, magnetization and neutron diffraction measurements. The substitution of Lu for Pr leads to a decrease in the lattice constants a, c and the unit cell volume V at room temperature with this contraction of the unit cell resulting in modifications of the Pr(1-x)Lu(x)Mn(2)Ge(2) magnetic structures. Four and five magnetic phase transitions-linked primarily with temperature driven changes in the intralayer Mn-Mn separation distances-have been detected within the temperature range 4.5-550 K for Pr(0.8)Lu(0.2)Mn(2)Ge(2) and Pr(0.6)Lu(0.4)Mn(2)Ge(2), respectively, with re-entrant ferromagnetism being detected around T(C)(Pr)∼31 K for Pr(0.6)Lu(0.4)Mn(2)Ge(2). It was found that T(C)(inter) and T(C)(Pr) increase with increasing applied field while T(N)(inter) decreases for Pr(0.6)Lu(0.4)Mn(2)Ge(2), indicating that the canted antiferromagnetic AFmc region contracts with increasing field. The Debye temperatures for Pr(1-x)Lu(x)Mn(2)Ge(2) with x = 0.2 and 0.4 were evaluated as θ(D) = 320 ± 40 K and θ(D) = 400 ± 20 K respectively from the temperature dependence of the average isomer shift. The magnetic structures of both compounds have been determined by means of neutron diffraction measurements over the temperature range 3-300 K with formation of the Fmi magnetic state below T(c/c) = 192 K for Pr(0.8)Lu(0.2)Mn(2)Ge(2) and the occurrence of re-entrant ferromagnetism below T(C)(Pr) = 31 K for Pr(0.6)Lu(0.4)Mn(2)Ge(2) being confirmed.

The magnetic properties and magnetic structures of PrMn2−xFexGe2 compounds (space group I4/mmm) have been investigated using magnetic, F57e Mossbauer effect (x=1.0,1.3,1.6), and neutron diffraction measurements (x=0.4,0.6,0.8,1.3) over the temperature range of 3–410 K. This has enabled the existing magnetic phase diagram for PrMn2−xFexGe2 to be extended from Fe concentration x=0–1 to the full range x=0–2 in terms of concentration and dMn–Mn, the intralayer distance. Analysis of the Mossbauer spectra (4.5–300 K) using a model which takes nearest-neighbor environments into account confirms the nonmagnetic nature of Fe atoms in these compounds, and leads to hyperfine parameters which deviate around the magnetic transition temperatures derived from the magnetic and neutron investigations while also enabling the Debye temperatures of PrMn2−xFexGe2 (x=0.4–1.6) to be determined. The experimental values for TCinter are found to decrease rapidly with increasing Fe concentration in the range x=0.0–0.6 compared with...

The polarization reversal mechanism in [111]c-oriented Pb(Zn1∕3Nb2∕3)O3−xPbTiO3 has been investigated by in-situ neutron diffraction. Stepwise static-field measurements of the (222)c rocking curves confirm a two-stage polarization reversal mechanism via a sequence of non-180° domain reorientations. The time-resolved response has also been measured upon application of a bipolar square wave with a 30 s period to observe directly the relaxation times of diffracted neutron intensity during the reversal process. Upon application of a large antipolar field, the diffraction intensity increases quickly, before relaxing over a longer time period with an exponential decay constant, τ, of approximately 5.7 s. These large time constants correlate with a frequency dependence of the macroscopic strain-field response.

The dynamic electric-field-induced strain in piezoelectric ceramics enables their use in a broad range of sensor, actuator, and electronic devices. In piezoelectric ceramics which are also ferroelectric, this macroscopic strain is comprised of both intrinsic (piezoelectric) and extrinsic (non-180° domain switching) strain components. Extrinsic contributions are accompanied by hysteresis, nonlinearity, and fatigue. Though technologically significant, direct measurement of these mechanisms and their relative contributions to the macroscopic response has not yet been achieved at driving frequencies of interest. Here we report measurements of these mechanisms in ceramic lead zirconate titanate during application of subcoercive cyclic driving electric fields using an in-situ stroboscopic neutron diffraction technique. Calculations are made from the diffraction measurements to determine the relative contributions of these different strain mechanisms. During applied electric field square waves of +0.5Ec unipolar...

The dynamic piezoelectric response of ferroelectric ceramics is comprised of both intrinsic (piezoelectric lattice strain) and extrinsic (non-180° domain wall motion) components. Here the authors report direct measurements of non-180° domain wall motion in ceramic lead zirconate titanate during application of subcoercive cyclic driving electric fields using an in situ stroboscopic neutron diffraction technique. During unipolar cycling at 1Hz and half of the coercive field, non-180° domain switching gives rise to approximately 34% of the measured d33 coefficient of 400pm∕V.

The magnetic structures of YbMn2Si2 with the tetragonal ThCr2Si2-type structure have been determined by neutron diffraction measurements over the temperature range ~1.5–538 K. Rietveld refinements demonstrate that YbMn2Si2 has a collinear antiferromagnetic structure below the Neel temperature TN1 = 526(4) K with the Mn moments parallel to the c-axis. Below TN2 ~ 30(5) K, the Mn sublattice rearranges to a +−−+ antiferromagnetic structure with propagation vector k = 00½. The moment direction is along the c-axis with a total moment of 1.92(8) μB at 10 K. There is no indication of ordering of the Yb ions at 10 K, although a diffraction pattern at 1.5 K shows that the Yb ions are ordered at the latter temperature. Analysis reveals that the Yb sublattice orders antiferromagnetically. The antiferromagnetically ordered Yb sublattice exhibits the same propagation vector, k = 00½, as the Mn sublattice, although the Yb spin directions are found to be perpendicular to the c-axis compared with the parallel alignment of the Mn moments. The refined value of the Yb3+ magnetic moment at 1.5 K is μYb = 0.57(9) μB compared with the free ion value of about 4.5 μB, while at 1.5 K the Mn magnetic moment is μMn = 1.98(7) μB.