I12-JEEP: Joint Engineering, Environmental and Processing
I15-Extreme Conditions
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Diamond Proposal Number(s):
[21147, 19558]
Abstract: The strength-ductility trade-off in additively manufactured (AM) β Ti alloys remains a significant challenge. In this study, we employed a cost-effective in-situ alloying laser powder bed fusion approach with optimized processing parameters to fabricate a nearly fully dense, chemically homogeneous β Ti-12Mo alloy. We then examined how solution-treatment duration influences the tensile behavior of the AM Ti-12Mo alloy. The optimally solution-treated alloys exhibited high tensile yield strength (725–741 MPa) and commendable ductility (22–36 %) along both the 0° and 90° orientations relative to the build direction. Focusing on the underlying deformation mechanisms perpendicular to the build direction, we report a uniform elongation of 17.9 % and a pronounced strain hardening rate (∼2300 MPa at 4 %), which we elucidate via in-situ high-energy synchrotron X-ray diffraction and microstructural characterization. The high yield strength is primarily attributed to the presence of Mo-lean embryonic athermal ω nanoparticles. During plastic deformation, both twinning and phase transformation contribute to the high strain hardening rate. At the early stage (strain < 1.9 %), deformation is dominated by {332}< 113 >β twinning, whereas at later stages, the deformation-induced α'' phase becomes significant. The volume fraction of α'' phase increases with strain, supporting the continuous hardening. Notably, irrational {112}< 751 >β, secondary {112}< 111 >β, and {130}< 310 >α'' nano-twins confine the primary structures to nanograins and sustain strain hardening. This study sheds light on designing high-performance β Ti-12Mo alloy via AM followed by heat treatment.
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Jun 2025
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I15-Extreme Conditions
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Diamond Proposal Number(s):
[39102]
Abstract: The Na3PnS4 (Pn = P, Sb) solid electrolytes are promising candidates for sodium solid-state batteries due to their potential high ionic conductivities. Structural modifications of these materials can induce a tetragonal-to-cubic phase transition, either by increasing temperature or by aliovalent substitutions. In this study, we introduce pressure as an alternative approach to observe the tetragonal-to-cubic phase transition in these materials. In situ synchrotron high-pressure powder X-ray diffraction shows a tetragonal-to-cubic phase transition at pressures of 2.9 GPa for Na3SbS4 and 14.6 GPa for Na3PS4. Rietveld refinements and symmetry analysis provide insights into the displacive phase transition mechanism related to the motion of Na+ and the rotation of the SbS43– tetrahedra. Density functional theory calculations confirm that the cubic phase becomes thermodynamically favorable under high pressure compared to the tetragonal phase. These findings highlight the importance of high-pressure considerations in tailoring the properties of ionic conductors, an area that remains underexplored.
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Jun 2025
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I15-Extreme Conditions
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Diamond Proposal Number(s):
[29285]
Open Access
Abstract: Copper(I) tricyanomethanide, Cu(tcm), is a flexible framework material that exhibits the strongest negative area compressibility (NAC) effect ever observed─a remarkable property with potential applications in pressure sensors, artificial muscles, and shock-absorbing devices. Under increasing pressure, Cu(tcm) undergoes two sequential phase transitions (tetragonal → orthorhombic → monoclinic): It has an initial tetragonal structure (I41md) at ambient conditions, but this structure only persists within a narrow pressure range; at 0.12(3) GPa, a pressure-induced ferroelastic phase transition occurs, transforming Cu(tcm) into a low-symmetry orthorhombic structure (Fdd2). The orthorhombic phase has a NAC of −108(14) TPa–1 in the b–c plane between 0.12(3) and 0.93(8) GPa. The NAC behavior is associated with framework hinge motion in a flexible framework with “wine-rack” topology. At 0.93(8) GPa, Cu(tcm) undergoes a second phase transition and transforms into a layered monoclinic structure (Cc) with topologically interpenetrating honeycomb networks. The monoclinic phase of Cu(tcm) exhibits a slight negative linear compressibility (NLC) of −1.1(1) TPa–1 along the a axis and a zero area compressibility of Kac = Ka + Kc = 0.0(4) TPa–1 in the a–c plane over the pressure range of 0.93–2.63 GPa. In contrast to the orthorhombic phase, its mechanism is understood as the pressure-driven dampening of layer “rippling,” which acts to increase the cross-sectional area of the layer at higher hydrostatic pressures. These findings have implications for understanding the underlying mechanism of NAC phenomenon in framework materials.
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May 2025
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I15-Extreme Conditions
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Diamond Proposal Number(s):
[30698]
Open Access
Abstract: Through laser-heated diamond anvil cell experiments, we synthesize a series of rubidium superhydrides and explore their properties with synchrotron x-ray powder diffraction and Raman spectroscopy measurements, combined with density functional theory calculations. Upon heating rubidium monohydride embedded in H2 at a pressure of 18 GPa, we form RbH9−I, which is stable upon decompression down to 8.7 GPa, the lowest stability pressure of any known superhydride. At 22 GPa, another polymorph, RbH9−II is synthesised at high temperature. Unique to the Rb-H system among binary metal hydrides is that further compression does not promote the formation of polyhydrides with higher hydrogen content. Instead, heating above 87 GPa yields RbH5, which exhibits two polymorphs (RbH5−I and RbH5−II). All of the crystal structures comprise a complex network of quasimolecular H2 units and H− anions, with RbH5 providing the first experimental evidence of linear H−
3 anions.
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May 2025
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I15-Extreme Conditions
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Open Access
Abstract: Various icy moons, such as Europa and Ganymede, have thin oxygen atmospheres and exhibit spectral features attributed to oxygen held in their surface ices. The oxygen forms from the radiolysis of water. The interiors of these bodies are subject to high pressures and it is not known how deep into icy moons oxygen-bearing ices can penetrate, or the structures formed by the oxygen–water system at high pressure. Here, we show that oxygen hydrates are stable to 2.6 GPa, allowing them to penetrate deep into icy moons, both above and below proposed sub-surface liquid-water oceans. Similarities between oxygen and hydrogen hydrates indicate potentially enhanced recombination rates, transforming them back into water and offering a resolution to the discrepancy between predicted and measured radiolysis rates. In addition to the low-pressure CS-II clathrate, our results find three high-pressure phases in the oxygen–water system: an ST clathrate, a C0 hydrate, and a filled ice isomorphous with methane hydrate III. This shows a vast storage potential for molecular oxygen in icy moons and indicates that Europa could still be absorbing oxygen into its crustal ice.
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Apr 2025
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I15-Extreme Conditions
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Diamond Proposal Number(s):
[31718]
Open Access
Abstract: NaNiO$_2$ is a Ni$^{3+}$-containing layered material consisting of alternating triangular networks of Ni and Na cations, separated by octahedrally-coordinated O anions. At ambient pressure, it features a collinear Jahn--Teller distortion below $T^\mathrm{JT}_\mathrm{onset}\approx480$\,K, which disappears in a broad first-order transition on heating to $T^\mathrm{JT}_\mathrm{end}\approx500$\,K, corresponding to the increase in symmetry from monoclinic to rhombohedral. It was previously studied by variable-pressure neutron diffraction [ACS Inorganic Chemistry 61.10 (2022): 4312-4321] and found to exhibit an increasing $T^\mathrm{JT}_\mathrm{onset}$ with pressure up to $\sim$5\,GPa. In this work, powdered NaNiO$_2$ was studied \textit{via} variable-pressure synchrotron x-ray diffraction up to pressures of $\sim$67\,GPa at 294\,K and 403\,K. Suppression of the collinear Jahn--Teller ordering is observed \textit{via} the emergence of a high-symmetry rhombohedral phase, with the onset pressure occurring at $\sim$18\,GPa at both studied temperatures. Further, a discontinuous decrease in unit cell volume is observed on transitioning from the monoclinic to the rhombohedral phase. These results taken together suggest that in the vicinity of the transition, application of pressure causes the Jahn--Teller transition temperature, $T^\mathrm{JT}_\mathrm{onset}$, to decrease rapidly. We conclude that the pressure-temperature phase diagram of the cooperative Jahn--Teller distortion in NaNiO$_2$ is dome-like.
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Apr 2025
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I15-Extreme Conditions
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Diamond Proposal Number(s):
[30553]
Open Access
Abstract: BiFeO3-BaTiO3 (BF-BT) solid solutions have great potential as high-temperature piezoelectric transducers and energy storage dielectrics. However, the effects of donor doping in BF-BT on the local chemical heterogeneity and corresponding control of ferroelectric properties are not well investigated. In this study, it is shown that substitution of Nb5+ for Fe3+ at a concentration of only 0.1 at% in 0.75BF-0.25BT ceramics can induce pronounced core-shell microstructural features, which are not evident for pure BF-BT ceramics or those doped with 0.1 at% Nb5+ for Ti4+. The spatial distribution of Nb, confirmed by Nano-SIMS with exceptional resolution and sensitivity, reveals the role of Nb as an aliovalent solute that inhibits chemical homogenization, stabilizing the formation of Bi-, Fe-enriched core and Ba-, Ti-enriched shell regions at high temperatures, and reducing inter-diffusion during sintering. Electric field-induced domain switching and lattice strain measurements, obtained by in-situ high-energy synchrotron X-ray diffraction, revealed the effects of elastic constraint between the core and shell regions, which degraded the dielectric, ferroelectric, and piezoelectric properties. In contrast, substitution of 0.1 at% Nb on the Ti4+ site gave rise to more homogeneous materials and induced a softening effect with enhanced functional properties. This study provides an advanced investigation into the effects of trace amounts of donor dopant in BF-BT ceramics and offers valuable insights into optimizing doping strategy to control their microstructure and functional properties.
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Mar 2025
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I15-Extreme Conditions
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Abstract: Nancyrossite, ideally FeGeO6H5, is a new hydroxyperovskite from Tsumeb. It likely formed by the oxidation and partial dehydrogenation of stottite, FeGe(OH)6, with which it is intimately associated. The structure of nancyrossite has been determined in tetragonal space group P42/n: a = 7.37382(12) Å, c = 7.29704(19) Å, V = 396.764(16) Å3, Z = 4, R1(all) = 0.034, wR2(all) = 0.051, GoF = 1.057. Empirical formulae of two crystals have almost end- member compositions, Fe3+1.01Zn0.03Ge0.98O6H5 and Fe3+1.01Zn0.04Ge0.98O6H5. Structure determination indicates that 88% Fe is ferric. The chemical formula proposed here for nancyrossite recognizes that although H atoms form OH groups, writing the formula as FeGeO(OH)5 implies that one of the six oxygen atoms is very underbonded, with a bond- valence sum of only ~1.2 v.u. As such, H in nancyrossite may have novel crystal chemistry. For example, the five H atoms may be distributed dynamically over the six O atoms, a phenomenon that would be averaged by X-ray diffraction, and so go undetected. Nancyrossite is the Ge-analogue of jeanbandyite. By analogy with nancyrossite, we propose revision of the ideal formula of jeanbandyite from FeSnO(OH)5 (Welch and Kampf, 2017) to FeSnO6H5.
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Feb 2025
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I15-Extreme Conditions
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Hannah A.
Shuttleworth
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Mikhail A.
Kuzovnikov
,
Lewis J.
Conway
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Huixin
Hu
,
Samuel
Gallego-Parra
,
Israel
Osmond
,
Tomas
Marqueno
,
Jinwei
Yan
,
Michael
Hanfland
,
Dominique
Laniel
,
Eugene
Gregoryanz
,
Andreas
Hermann
,
Miriam
Pena-Alvarez
,
Ross T.
Howie
Diamond Proposal Number(s):
[30698]
Open Access
Abstract: Carbon, nitrogen, and hydrogen are among the most abundant elements in the solar system, and our understanding of their interactions is fundamental to prebiotic chemistry. CH4 and N2 are the simplest archetypical molecules formed by these elements and are both markedly stable under extremes of pressure. Through a series of diamond anvil cell experiments supported by density functional theory calculations, we observe diverse compound formation and reactivity in the CH4-N2 binary system at high pressure. Above 7 GPa two concentration-dependent molecular compounds emerge, (CH4)5N2 and (CH4)7(N2)8, held together by weak van der Waals interactions. Strikingly, further compression at room temperature irreversibly breaks the N2 triple bond, inducing the dissociation of CH4 above 140 GPa, with the near-quenched samples revealing distinct spectroscopic signatures of strong covalently bonded C−N−H networks. High temperatures vastly reduce the required pressure to promote the reactivity between CH4 and N2, with NH3 forming together with longer-chain hydrocarbons at 14 GPa and 670 K, further decomposing into powdered diamond when temperatures exceed 1200 K. These results exemplify how pressure-driven chemistry can cause unexpected complexity in the most simple molecular precursors.
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Feb 2025
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I11-High Resolution Powder Diffraction
I15-1-X-ray Pair Distribution Function (XPDF)
I15-Extreme Conditions
I20-EDE-Energy Dispersive EXAFS (EDE)
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Diamond Proposal Number(s):
[31314, 31898, 20038, 29957, 30178]
Abstract: Metal-organic frameworks (MOFs) are a versatile class of hybrid inorganic-organic materials known for their adjustable chemical and physical properties, as well as their exceptional porosity. These characteristics render MOFs particularly valuable for applications requiring extensive surface areas, such as gas storage and catalysis. Despite being advantageous in many applications, the high porosity and specific bonding characteristics of crystalline MOFs can, however, make them susceptible to pore collapse and amorphisation under pressure. This limits the practical effectiveness of MOFs in their most commonly synthesised form of crystalline powders, as large-scale production and shaping of powders for industrial use often involves pressure and heating.
This thesis examines how a range of MOFs behave under various high pressure and high pressure-temperature conditions to examine both their amorphisation mechanisms and amorphous phases formed. The MOFs were selected to fall within two groups: zirconium-based (UiO-66, MOF-808 and NU-1000) and zinc-based (ZIF-8, ZIF-4 and ZIF-62). The methods chosen for investigations were hydrostatic compression, non-hydrostatic compression, and ball-milling, as they are all used for industrial processing of powders: The former two are methods for shaping, and the latter for mixing. Hydrostatic compression of these MOFs is investigated in depth through in situ high pressure-temperature crystallographic and spectroscopic measurements, allowing real-time analysis on the MOFs’ collapse mechanisms. Both groups display partially reversible amorphisation under hydrostatic compression to certain pressures, indicating a displacive amorphisation transition into an amorphous phase topologically similar to the crystalline. Penetration of the pressure-transmitting media into the framework’s pores was also indicated in each MOF, with clear negative volume compressibility shown in the zinc-based MOFs.
Ex situ investigations into non-hydrostatic compression then introduce the effect of shear stress so its effect on the MOFs can be highlighted, where the two groups demonstrate quite different behaviour attributed to differences in the connectivity of their inorganic components. Ball-milling is finally examined as a non-compression form of amorphisation with a high shear component. In both shear-based pressure states, decoordination of the organic components from the inorganic is seen as a driving factor of amorphisation. Understanding the collapse mechanisms and resultant amorphous phases from various amorphisation methods in these MOFs gives insight into trends in mechanical properties and stability within this class of materials, and is essential for the future industrialisation of MOFs.
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Jan 2025
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