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The functional properties of piezoelectric ceramic materials, such as barium titanate, are highly dependent on grain size. Lead-free polycrystalline Ba0.85Ca0.15Zr0.1Ti0.9O3 (BCZT) samples were prepared with a combination of the hydrothermal method and spark plasma sintering to achieve grain sizes from 100 nm to 10 μm by varying the maximum sintering temperature. In this range, a transition from a nearly linear dielectric to a ferroelectric response can be seen in macroscopic electromechanical measurements, demonstrating the importance of grain size on functional properties in BCZT. Furthermore, in situ electric field-dependent synchrotron x-ray diffraction measurements were performed to quantify the intrinsic and extrinsic strain contributions and their variations with grain size. At lower grain sizes, the data revealed a significant loss of extrinsic contributions in the piezoelectric behavior, limiting the response to intrinsic contribution associated with lattice strain. For BCZT, a critical grain size between approximately 0.08 and 0.18 μm is proposed, below which no piezoelectric response was observed. [ABSTRACT FROM AUTHOR]

Raman spectra in the range 80 to 4000 [cm.sup.-1] of wadsleyite II ([Fo.sub.90] with 2.0 wt% [H.sub.2]O and [Fo.sub.88] with 2.7 wt% [H.sub.2]O) have been measured in a diamond-anvil cell with solid rare-gas pressure-transmitting media to 51.4 GPa at room temperature. The ambient Raman spectrum of wadsleyite II is closely similar to wadsleyite modified with bands in frequency regions where the Si[O.sub.4] tetrahedral and OH stretching vibrations of hydrous ringwoodite occur. The most intense, characteristic wadsleyite II modes at 709 and 911 [cm.sup.-1] ([Si.sub.2][O.sub.7] and Si[O.sub.3] symmetric stretching vibrations, respectively) shift continuously to 51.4 GPa showing no evidence for a change in the crystal structure. A striking feature in the high-pressure Raman spectra of wadsleyite II is a significant growth in intensity in the mid-frequency range (300-650 [cm.sup.-1] at [10.sup.-4] GPa and 400-750 [cm.sup.-1] at 51.4 GPa) under compression accompanied by the appearance of new Raman modes near 40 GPa, perhaps a result of resonance electronic Raman scattering. In the OH stretching frequency range, the Raman spectrum of wadsleyite II exhibits at least six modes and their high-pressure behavior agrees with that of [Fo.sub.90] hydrous wadsleyite: OH stretching modes above 3530 [cm.sup.-1] remain approximately constant up to at least 21.8 GPa whereas OH modes at frequencies Keywords: Hydrous wadsleyite II, Raman spectroscopy, diamond-anvil cell, transition zone, high pressure

The high-pressure behavior of synthetic end-member IIb clinochlore, [Mg.sub.5]Al([Si.sub.3]Al)[O.sub.10][(OH).sub.8], has been studied by synchrotron X-ray powder diffraction to 27 GPa at 300 K. A non-quenchable, reversible transformation occurs between 9 and 10 GPa that is dominated by compression normal to the structural layering and has an associated small but significant shear of the 13 angle from 97.2 to 96.3[degrees]. The high-pressure chlorite is more compressible than the low-pressure phase. Diffraction patterns of the high-pressure chlorite are very similar from 10 to 27 GPa, indicating that it persists stably with no significant change in [beta] to very high pressures: [beta] is effectively locked at the transformation to the high-pressure structure. It is proposed that the transformation is not polytypic and that the distortion reflects reorganization of the interlayer hydrogen bonding, possibly involving novel proton behavior as adjacent sheets of cations of the brucite-like and tetrahedral layers close down on the sheet of interlayer protons. The transformation is likely driven by O atom close-packing requirements imposed by pressure.

The effect of pressure upon hydrogen bonding in synthetic end-member clinochlore, ([Mg.sub.5]Al)([Si.sub.3]Al)[O.sub.10][(OH).sub.8], has been studied in situ by high-pressure micro-Raman spectroscopy in a moissanite-anvil cell to 26.5 GPa at 300 K. The ambient spectrum consists of three OH-stretching bands between 3400 and 3650 [cm.sup.-1], attributed to the hydrogen-bonded interlayer OH, and a narrow band at 3679 [cm.sup.-1] that is assigned to the non-hydrogen-bonded OH groups of the talc-like 2:1 layer. The pressure dependence of the OH modes is linear up to 6 GPa. Near 9 GPa a major discontinuity occurs in the pressure dependence of the interlayer OH-stretching modes. It involves frequency increases >100 [cm.sup.-1] that indicate major changes in hydrogen bonding. The OH mode of the 2:1 layer does not show discontinuous behavior at 9 GPa. A further discontinuity occurs at ~16 GPa. This discontinuity affects both interlayer and 2:1 OH, and is likely to be associated with a change in the overall compression mechanism of clinochlore. The spectroscopic behavior is a completely reversible function of pressure. Predictions based upon recent high-pressure diffraction studies of hydrogen bonding and compression of clinochlore suggest that the 9 GPa transition is associated with attainment of an [O.sup.2-]-[O.sup.2] -contact distance of 2.7 [Angstrom].

Author(s): Martin D. Brasier (corresponding author) [1]; Owen R. Green [1]; Andrew P. Jephcoat [1]; Annette K. Kleppe [1]; Martin J. Van Kranendonk [2]; John F. Lindsay [3]; Andrew Steele [...]

Experiments involving the irradiation of water contained within magnesium hydroxide and alumina nanoparticle sludges were conducted and culminated in observations of an increased yield of molecular hydrogen when compared to the yield from the irradiation of bulk water. We show that there is a relationship linking this increased yield to the direct nanoscale ionization mechanism in the nanoparticles, indicating that electron emission from the nanoparticles drives new radiative pathways in the water. Because the chemical changes in these sludges are introduced by irradiation only, we have a genuinely unstirred system. This feature allows us to determine the diffusivity of the dissolved gas. Using the measured gas production rate, we have developed a method for modelling when hydrogen bubble formation will occur within the nanoparticle sludges. This model facilitates the determination of a consistent radiolytic consumption rate coinciding with the observations of bubble formation. Thus, we demonstrate a nanoscale radiation effect directly influencing the formation of molecular hydrogen. [ABSTRACT FROM AUTHOR]

High pressure–temperature experiments provide information on the phase diagrams and physical characteristics of matter at extreme conditions and offer a synthesis pathway for novel materials with useful properties. Experiments recreating the conditions of planetary interiors provide important constraints on the physical properties of constituent phases and are key to developing models of planetary processes and interpreting geophysical observations. The laser-heated diamond anvil cell (DAC) is currently the only technique capable of routinely accessing the Earth's lower-mantle geotherm for experiments on non-metallic samples, but large temperature uncertainties and poor temperature stability limit the accuracy of measured data and prohibits analyses requiring long acquisition times. We have developed a novel internal resistive heating (IRH) technique for the DAC and demonstrate stable heating of non-metallic samples up to 3000 K and 64 GPa, as confirmed by in situ synchrotron x-ray diffraction and simultaneous spectroradiometric temperature measurement. The temperature generated in our IRH-DAC can be precisely controlled and is extremely stable, with less than 20 K variation over several hours without any user intervention, resulting in temperature uncertainties an order of magnitude smaller than those in typical laser-heating experiments. Our IRH-DAC design, with its simple geometry, provides a new and highly accessible tool for investigating materials at extreme conditions. It is well suited for the rapid collection of high-resolution P–V–T data, precise demarcation of phase boundaries, and experiments requiring long acquisition times at high temperature. Our IRH technique is ideally placed to exploit the move toward coherent nano-focused x-ray beams at next-generation synchrotron sources. [ABSTRACT FROM AUTHOR]

Alkali‐silica reaction (ASR) causes severe degradation of concrete. The mechanical property of the ASR product is fundamental to the multiscale modeling of concrete behavior over the long term. Despite years of study, there is a lack of consensus regarding the structure and elastic modulus of the ASR product. Here, ASR products from both degraded field infrastructures and laboratory synthesis were investigated using high‐pressure X‐ray diffraction. The results unveiled the multiphase and metastable nature of ASR products from the field. The dominant phase undergoes permanent phase change via collapsing of the interlayer region and in‐planar glide of the main layer, under pressure >2 GPa. The bulk moduli of the low‐ and high‐pressure polymorphs are 27±3 and 46±3 GPa, respectively. The laboratory‐synthesized sample and the minor phase in the field samples undergo no changes of phase during compression. Their bulk moduli are 35±2 and 76±4 GPa, respectively. The results provide the first atomistic‐scale measurement of the mechanical property of crystalline ASR products. [ABSTRACT FROM AUTHOR]

High electrostrain and breakdown strength (1 − x)BiFeO3-0.3BaTiO3-xNd(Li0.5Nb0.5)O3 (BF-BT-xNLN) ceramics were studied by in situ synchrotron X-ray diffraction (XRD) in combination with Rietveld refinement and conventional transmission electron microscopy. At zero field, compositions transformed from majority ferroelectric rhombohedral to pseudocubic as the NLN concentration increased, with 0.27% strain achieved at 60 kV cm−1 for x = 0.01. The large measured macroscopic strain was commensurate with peak shifting in XRD peak profiles, yielding 0.6% total strain at 150 kV cm−1. Strain anisotropy of ε200 > ε220 > ε111 was observed but despite the large applied field, no peak splitting was detected. We therefore concluded that the large electrostrain is not achieved through a conventional relaxor to field induced long-range ferroelectric transition. Instead, the data supports a model where local polar regions distort in the direction of the applied field within multiple local symmetries (pseudosymmetry) without long range correlation. We proposed that pseudosymmetry is maintained in BF-BT-xNLN even at high field (150 kV cm−1) due to the large ion radii mismatch and competing ionic/covalent bonding between Ba2+ and Bi3+ ions. [ABSTRACT FROM AUTHOR]

Electromechanical actuation in piezoceramics is usually enhanced by creating chemically homogeneous materials with structurally heterogeneous morphotropic phase boundaries, leading to abrupt changes in ion displacement directions within the perovskite unit cell. In the present study, an alternative mechanism to enhance electromechanical coupling is found in both chemically and structurally heterogeneous BiFeO3–BaTiO3 lead-free piezoceramics. Such a mechanism is observed in a composition exhibiting core–shell type microstructure, associated with donor-type substitution of Ti4+ for Fe3+, and is primarily activated by thermal quenching treatment. Here, we describe the use of in situ high-energy synchrotron X-ray powder diffraction upon the application of a high electric field to directly monitor the ferroelectric and elastic interactions between these composite-like components, formed as core and shell regions within grains. Translational short or long-range ordering is observed in the BiFeO3-depleted shell regions which undergo significant structural alterations from pseudocubic Pm3¯m relaxor-ferroelectric in slow-cooled ceramics to rhombohedral R3c or R3m with long-range ferroelectric order in the quenched state. The strain contributions from each component are calculated, leading to the conclusion that the total macroscopic strain arises predominantly from the transformed shell after quenching. Such observations are also complemented by investigations of microstructure and electrical properties, including ferroelectric behaviour and temperature-dependent dielectric properties. [ABSTRACT FROM AUTHOR]

In this article, the specification and application of the new double‐sided YAG laser‐heating system built on beamline I15 at Diamond Light Source are presented. This system, combined with diamond anvil cell and X‐ray diffraction techniques, allows in situ and ex situ characterization of material properties at extremes of pressure and temperature. In order to demonstrate the reliability and stability of this experimental setup over a wide range of pressure and temperature, a case study was performed and the phase diagram of lead was investigated up to 80 GPa and 3300 K. The obtained results agree with previously published experimental and theoretical data, underlining the quality and reliability of the installed setup. A double‐sided, off‐axis laser‐heating system for monochromatic X‐ray diffraction experiments using a diamond anvil cell has been installed at beamline I15 at Diamond Light Source. Measurements of the pressure–temperature phase diagram of Pb demonstrate the reliability of the setup and the high quality of the data. [ABSTRACT FROM AUTHOR]

The paper is concerned with the structure and functional properties of bismuth ferrite–barium titanate, 0.75BiFeO3–0.25BaTiO3, solid solutions. Such materials are attracting attention due to their potential applications in high temperature piezoelectric transducers for use in demanding environments in process monitoring, for example. The article focuses on the mechanism of incorporation of the minor dopant lanthanum oxide, either in the form of isovalent or donor-type substitution. It is shown that the development of chemical heterogeneity in the form of core–shell grain microstructures, linked to donor-type substitution, plays a key role in controlling the functional behaviour. The use of an air-quenching procedure results in dramatic improvements in the ferroelectric properties, accompanied by a transformation of the shell regions from a pseudo-cubic, Pm3̅m, to rhombohedral, R3c, structure. These observations are interpreted in terms of a novel mechanism involving nanoscale phase separation in the ‘shell’ regions during slow cooling, which impedes the development of ferroelectric ordering and leads to the formation of a nano-polar relaxor ferroelectric state. The work highlights the importance of immiscibility in bismuth-based ferroelectric perovskite solid solutions and illustrates how their ferroelectric, piezoelectric, dielectric energy storage, ferromagnetic and magneto-electric properties can be tuned by consideration of the substitution mechanism and control of thermal processing parameters. [ABSTRACT FROM AUTHOR]

The poling behaviour of tetragonal lead zirconate titanate (PZT) piezoelectric ceramic particles in a weakly conductive ionomer polymer matrix is investigated using high energy synchrotron X-ray diffraction analysis. The poling efficiency, crystallographic texture and lattice strain of the PZT particles inside the polymer matrix are determined and compared with the values for corresponding bulk ceramics reported in literature. The volume fraction of c-axis oriented domains and the lattice strain of the PZT particles are calculated from the changes in the integral intensities of the {200} peaks and the shift in the position of the {111} peaks respectively. It is shown that for an applied macroscopic field of 15 kV.mm−1, the PZT particles are effectively poled, leading to a maximum ν(002) domain reorientation volume fraction, of around 0.70. It is also found that a significant tensile lattice strain, ϵ{111}, of 0.6% occurs in the direction of the applied electric field, indicating the occurrence of residual stresses within the 2–4 μm size diameter particles. Although lower than that observed in poled tetragonal PZT ceramics, this level of lattice strain does indicate that the PZT particles within the composite experience significant elastic constraint. The correlation between the poling induced structural changes and the macroscopic piezoelectric and dielectric properties is discussed. [ABSTRACT FROM AUTHOR]

Quantification of residual stress gradients can provide great improvements in understanding the complex interactions between microstructure, mechanical state, mode(s) of failure and structural integrity. Highly focused local probe non-destructive techniques such as X-ray diffraction, electron diffraction or Raman spectroscopy have an established track record in determining spatial variations in the relative changes in residual stress with respect to a reference state for many structural materials. However, the interpretation of these measurements in terms of absolute stress values requires a strain-free sample often difficult to obtain due to the influence of chemistry, microstructure or processing route. With the increasing availability of focused ion beam instruments, a new approach has been developed which is known as the micro-scale ring-core focused ion beam-digital image correlation technique. This technique is becoming the principal tool for quantifying absolute in-plane residual stresses. It can be applied to a broad range of materials: crystalline and amorphous metallic alloys and ceramics, polymers, composites and biomaterials. The precise nano-scale positioning and well-defined gauge volume of this experimental technique make it eminently suitable for spatially resolved analysis, that is, residual stress profiling and mapping. Following a summary of micro-stress evaluation approaches, we focus our attention on focused ion beam-digital image correlation methods and assess the application of micro-scale ring-core methods for spatially resolved residual stress profiling. The sequential ring-core milling focused ion beam-digital image correlation method allows micro- to macro-scale mapping at the step of 10–1000 μm, while the parallel focused ion beam-digital image correlation approach exploits simultaneous milling operation to quantify stress profiles at the micron scale (1–10 μm). Cross-validation against X-ray diffraction results confirms that these approaches represent accurate, reliable and effective residual stress mapping methods. [ABSTRACT FROM AUTHOR]

The application of pressure to materials can reveal unexpected chemistry. Under compression, noble gases form stoichiometric van der Waals (vdW) compounds with closed-shell molecules such as hydrogen, leading to a variety of unusual structures. We have synthesised Kr(H2)4 for the first time in a diamond-anvil high-pressure cell at pressures≥5.3 GPa and characterised its structural and vibrational properties to above 50 GPa. The structure of Kr(H2)4, as solved by single-crystal synchrotron X-ray diffraction, is face-centred cubic (fcc) with krypton atoms forming isolated octahedra at fcc sites. Rotationally disordered H2 molecules occupy four different, interstitial sites, consistent with the observation of four Raman activeH2 vibrons. The discovery of Kr(H2)4 expands the range of pressure-stabilised, hydrogen-rich vdW solids, and, in comparison with the two known rare-gas-H2 compounds, Xe(H2)8 and Ar(H2)2, reveals an increasing change in hydrogen molecular packing with increasing rare gas atomic number. [ABSTRACT FROM AUTHOR]

Durch Druckeinwirkung auf den herkömmlichen Zeolith ITQ ‐ 29 gelang erstmals die druckinduzierte Festphasensynthese eines Zeoliths (siehe Schema; Si gelb, O rot): Das Produkt, ITQ ‐ 50, hat eine einzigartige mikroporöse Struktur und ist leistungsfähiger in der Propen ‐ Propan ‐ Trennung als das Ausgangsmaterial ITQ ‐ 29. [ABSTRACT FROM AUTHOR]

Presents a study which measured the Raman spectra of phase E in a diamond-anvil cell. Raman active frequencies of phase E at ambient conditions; Pressure dependence of the Raman frequencies of phase E; Discussion on the framework of Raman bands.

The isothermal equation of state of silicon has been determined by synchrotron x-ray diffraction experiments up to 105.2 GPa at room temperature using diamond anvil cells. A He-pressure medium was used to minimize the effect of uniaxial stress on the sample volume and ruby, gold and tungsten pressure gauges were used. Seven different phases of silicon have been observed along the experimental conditions covered in the present study. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • Microscale resolution residual strain mapping inside porcelain veneer. • Pair distribution function X-ray diffraction quantification using new technique. • Ring-core focused ion beam and digital image correlation cross-validation. • Comparable results, with tensile strain maximum on inner surface. • Oscillatory strains associated with layering manufacture approach observed. Abstract Objective Residually strained porcelain is influential in the early onset of failure in Yttria Partially Stabilised Zirconia (YPSZ) – porcelain dental prosthesis. In order to improve current understanding it is necessary to increase the spatial resolution of residual strain analysis in these veneers. Methods Few techniques exist which can resolve residual stress in amorphous materials at the microscale resolution required. For this reason, recent developments in Pair Distribution Function (PDF) analysis of X-ray diffraction data of dental porcelain have been exploited. This approach has facilitated high-resolution (70 μm) quantification of residual strain in a YPSZ-porcelain dental prosthesis. In order to cross-validate this technique, the sequential ring-core focused ion beam and digital image correlation approach was implemented at a step size of 50 μm. This semi-destructive technique exploits microscale strain relief to provide quantitative estimates of the near-surface residual strain. Results The two techniques were found to show highly comparable results. The residual strain within the veneer was found to be primarily tensile, with the highest magnitude stresses located at the YPSZ-porcelain interface where failure is known to originate. Oscillatory tensile and compressive stresses were also found in a direction parallel to the interface, likely to be induced by the multiple layering used during fabrication. Significance This study provides the insights required to improve prosthesis modelling, to develop new processing routes that minimise residual stress and ultimately to reduce prosthesis failure rates. The PDF approach also offers a powerful new technique for microscale strain quantification in amorphous materials. [ABSTRACT FROM AUTHOR]

Abstract We report on laser-heated diamond anvil cell (LHDAC) experiments in the FeO–MgO–SiO 2 –CO 2 (FMSC) and CaO–MgO–SiO 2 –CO 2 (CMSC) systems at lower mantle pressures designed to test for decarbonation and diamond forming reactions. Sub-solidus phase relations based on synthesis experiments are reported in the pressure range of ∼35 to 90 GPa at temperatures of ∼1600 to 2200 K. Ternary bulk compositions comprised of mixtures of carbonate and silica are constructed such that decarbonation reactions produce non-ternary phases (e.g. bridgmanite, Ca-perovskite, diamond, CO 2 –V), and synchrotron X-ray diffraction and micro-Raman spectroscopy are used to identify the appearance of reaction products. We find that carbonate phases in these two systems react with silica to form bridgmanite ±Ca-perovskite + CO 2 at pressures in the range of ∼40 to 70 GPa and 1600 to 1900 K in decarbonation reactions with negative Clapeyron slopes. Our results show that decarbonation reactions form an impenetrable barrier to subduction of carbonate in oceanic crust to depths in the mantle greater than ∼1500 km. We also identify carbonate and CO 2 –V dissociation reactions that form diamond plus oxygen. On the basis of the observed decarbonation reactions we predict that the ultimate fate of carbonate in oceanic crust subducted into the deep lower mantle is in the form of refractory diamond in the deepest lower mantle along a slab geotherm and throughout the lower mantle along a mantle geotherm. Diamond produced in oceanic crust by subsolidus decarbonation is refractory and immobile and can be stored at the base of the mantle over long timescales, potentially returning to the surface in OIB magmas associated with deep mantle plumes. Highlights • Experiments were made in the systems FMS-CO2 and CMS-CO2 at lower mantle pressures. • Carbonate in these systems react with silica in the lower mantle. • Decarbonation reactions with negative P–T slopes form CO 2 or diamond plus oxygen. • Carbonate in oceanic crust is limited to ∼1500 km depth along subduction geotherms. • Diamond is the stable form of carbon in oceanic crust at ambient mantle temperature. [ABSTRACT FROM AUTHOR]

High-energy x-ray diffraction data from a series of amorphous ZrW2O8 samples, recovered from a number of different pressures, have been measured and compared with similar data collected from a sample contained within a diamond anvil cell and measured in situ at high pressure. Samples at lower pressures are a mix of crystalline and amorphous phases, whereas those above 7 GPa (both recovered and in situ) appear to be completely amorphous. Although there are only very small changes in the diffraction data from the pure phase samples recovered from different pressures, larger changes are observed in situ as a function of pressure. However, the same structural model can be used to describe all data, albeit using different densities. This strongly suggests that the amorphous phase is undergoing nonreconstructive compression in this pressure range, without fundamental modification of the underlying topology. [ABSTRACT FROM AUTHOR]

The atomic-scale structure, melting curve, and equation of state of liquid gallium has been measured to high pressure (p) and high temperature (T) up to 26 GPa and 900 K by in situ synchrotron x-ray diffraction. Ab initio molecular dynamics simulations up to 33.4 GPa and 1000 K are in excellent agreement with the experimental measurements, providing detailed insight at the level of pair distribution functions. The results reveal an absence of dimeric bonding in the liquid state and a continuous increase in average coordination number n̅GaGa from 10.4(2) at 0.1 GPa approaching ~12 by 25 GPa. Topological cluster analysis of the simulation trajectories finds increasing fractions of fivefold symmetric and crystalline motifs at high p-T. Although the liquid progressively resembles a hard-sphere structure towards the melting curve, the deviation from this simple description remains large (=40%) across all p-T space, with specific motifs of different geometries strongly correlating with low local two-body excess entropy at high p-T. [ABSTRACT FROM AUTHOR]