I11-High Resolution Powder Diffraction
I15-Extreme Conditions
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Diamond Proposal Number(s):
[14061, 17673, 16390]
Open Access
Abstract: The similar electronic structures of Bi3+ and Pb2+ have motivated researchers to explore bismuth-based perovskite compounds, which in the past decade has been further fuelled by the demand for developing lead-free piezoceramics. The difficulty in stabilizing the perovskite phase in bismuth based compounds has directed most research activities towards exploring two main compounds - multiferroic BiFeO3 and relaxor ferroelectric Na1/2Bi1/2TiO3 and their derivatives. In recent years, quenching these materials from the sintering temperature or from the paraelectric phase (above the Curie temperature, Tc) has resulted in a plethora of fundamentally interesting and technologically relevant advances, including enhanced thermal depolarization temperature, high Tc, giant strain and control over the atomic structure and electrical conductivity at the domain wall. In this contribution, a brief overview of quenching piezoceramics is presented, with majority of the discussion encompassing salient features of quenching lead-free perovskite structured Na1/2Bi1/2TiO3- and BiFeO3- based materials. For each material system, the influence of quenching on phase transitions, domain switching behavior and electromechanical properties are presented, apart from outlining the current understanding of the underlying mechanisms. The review provides guidelines for further exploration of the quenching strategy for improving the functionality of Bi-based piezoceramics.
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May 2022
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I15-Extreme Conditions
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Diamond Proposal Number(s):
[17412, 8858]
Abstract: The effect of H+ ion irradiation on the structure and properties of a Cu50Zr50 metallic glass (MG) was investigated. High energy synchrotron X-ray diffraction results indicate that the glass maintains its amorphous nature after ion irradiation. As the ion fluence increases, the atomic bond length of MGs becomes shorter, whereas the nanohardness and Young’s modulus increase from 7.08±0.01 GPa and 111.3±1.1 GPa for the as-spun sample to 8.59±0.06 GPa and 123.1±1.3 GPa for the sample irradiated with 2×1016 cm-2 fluence. The corrosion potential of the studied MG in 1 mol/L HCl increases from -0.5953 V to -0.4519 V, suggesting an enhanced corrosion resistance of MGs after ion irradiation. The modification of mechanical properties and corrosion resistance can be interpreted from the ion irradiation-induced structural evolution. The results obtained here can be beneficial for better understanding the mechanical properties and corrosive behaviors of MGs under extreme conditions like ion irradiation and thus promoting their industrial applications.
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Apr 2022
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I15-Extreme Conditions
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Diamond Proposal Number(s):
[26452, 28469]
Open Access
Abstract: The high-pressure and high-temperature phase diagram of chromium has been investigated both experimentally (in situ), using a laser-heated diamond-anvil cell technique coupled with synchrotron powder X-ray diffraction, and theoretically, using ab initio density-functional theory simulations. In the pressure–temperature range covered experimentally (up to 90 GPa and 4500 K, respectively) only the solid body-centred-cubic and liquid phases of chromium have been observed. Experiments and computer calculations give melting curves in agreement with each other that can both be described by the Simon–Glatzel equation 𝑇𝑚(𝑃)=2136𝐾(1+𝑃/25.9)0.41
T
m
(
P
)
=
2136
K
(
1
+
P
/
25.9
)
0.41
. In addition, a quasi-hydrostatic equation of state at ambient temperature has been experimentally characterized up to 131 GPa and compared with the present simulations. Both methods give very similar third-order Birch–Murnaghan equations of state with bulk moduli of 182–185 GPa and respective pressure derivatives of 4.74–5.15. According to the present calculations, the obtained melting curve and equation of state are valid up to at least 815 GPa, at which pressure the melting temperature is 9310 K. Finally, from the obtained results, it was possible to determine a thermal equation of state of chromium valid up to 65 GPa and 2100 K.
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Apr 2022
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I15-Extreme Conditions
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Diamond Proposal Number(s):
[24144]
Open Access
Abstract: In situ, spatially-resolved synchrotron X-ray diffraction was utilized to investigate the electric field-induced heterogenous phase transformation of nonergodic relaxor 0.93Na1/2Bi1/2TiO3-0.07BaTiO3 ceramics. A Cu electrode was coated on one surface of a rectangular sample by aerosol deposition (AD), while a Pt layer was deposited on the opposite surface by sputter deposition. It is anticipated that a different stress state and/or domain morphology should occur on the AD deposited Cu electrode side due to the particle impact-consolidation deposition process. Under an electric field, different sample regions, i.e., AD, Middle, and Sputter sides, showed systematic changes in the relaxor to ferroelectric phase transition behavior. In particular, most <001> grains transformed at a sub-coercive field of 0.8 kV/mm, while the majority of the <111> grains only appeared to undergo transitions at a higher field (2.4 kV/mm). Also, the tetragonal phase became the dominant structure at higher field levels. Importantly, both <111> and <001> grains undergo phase switching at lower fields in the region close to the AD-processed layer. The study indicates that the AD process-induced stress can facilitate the electric field-induced relaxor to ferroelectric phase transition, i.e., the AD Cu side showed more significant lattice strain and domain texture than the sputter Pt side.
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Mar 2022
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I15-Extreme Conditions
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Abstract: The lanthanide and actinide metals have complex electronic and magnetic
behaviour at high pressures and low temperatures, respectively, owing to the
f electrons buried within the atoms participating in the bonding of those metals.
As one traverses the lanthanide series with increasing Z at ambient conditions,
each element adds one electron to the 4f shell, starting with cerium (Ce) and
ending with a full 4f electron shell in lutetium (Lu). This thesis focuses on
the trivalent lanthanides, which are considered to be all the lanthanides except
Ce, europium (Eu) and ytterbium (Yb), and their structural systematics at
high pressures. The trivalent lanthanides exhibit a common, pressure-induced,
structural phase transition sequence: hexagonal close-packed (hcp) ! Sm-type
or -Sm ! double-hcp (dhcp) ! face-centred cubic (fcc) ! distorted-fcc (dfcc)
! \volume-collapsed". This sequence is thought to arise from the 5s ! 5d
transfer of electrons, and, at ultra-high pressures, from the 4f electrons becoming
delocalised and then participating in the bonding of these elements, leading to
volume-collapsed phases with low-symmetry structures. However, there is still
debate over the exact structures of the low-symmetry collapsed phases.
This thesis describes x-ray di raction studies of the high-pressure structures of the
collapsed phases of six trivalent lanthanide elements (neodymium (Nd), samarium
(Sm), praseodymium (Pr), gadolinium (Gd), terbium (Tb) and dysprosium
(Dy)), and also yttrium (Y) { a rare-earth element. Using diamond anvil cell
(DAC) techniques and x-ray powder di raction at the Diamond Light Source
and PETRA-III synchrotrons, the structures of the collapsed phases of six of the
seven elements are found to be face-centred orthorhombic, spacegroup Fddd, with
either 8 atoms (Nd and Sm) or 16 atoms (Gd, Tb, Dy and Y) in the unit cell.
The 8-atom structure (oF8) is the same as that seen previously in the actinides
plutonium (Pu), americium (Am), curium (Cm) and californium (Cf), greatly
strengthening the structural relationships between the 4f lanthanides and the 5f
actinides. The 16-atom structure (oF16) found in Gd, Tb, Dy and Y is previously
unknown in the elements, but, along with the oF8 structure, and hP3 structure
seen in Nd and Sm at lower pressures, it is a member of a new structural family
comprising di erent stackings of quasi-hcp layers.
This thesis also describes higher-pressure studies with the aim of determining the
structural systematics of the post-oF8/oF16 phases. Pr and Nd have been shown
to exhibit the -uranium ( -U) structure, oC4, in their collapsed phases. In Pr,
a primitive orthorhombic structure was previously reported above 147 GPa, the
post- -U phase, a structure not seen in any other element. This thesis shows that
the true structure is body-centred tetragonal, the same as the highest-pressure
phase seen in the neighbouring lanthanide Ce, and also in the actinides thorium
(Th) and uranium (U), suggesting that it is the \next" structure in the transition
sequence of the trivalent lanthanides.
This work contained in this thesis completely rewrites the structural behaviour
of the trivalent lanthanide elements at high-pressure and reveals that the highpressure
behaviour of the lanthanide and actinide metals is much more similar
than previously believed.
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Mar 2022
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I15-Extreme Conditions
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Diamond Proposal Number(s):
[8858, 9902]
Abstract: We studied in situ the local atomic structure evolution of an equiatomic
Zr
50
Cu
50
metallic glassy alloy under high pressure compression inside a diamond anvil cell using synchrotron x-ray total scattering. The empirical potential structure refinement method was used to reconstruct the three-dimensional atomic models at each pressure step, and to analyze the spatially averaged local atomic structure configurations. The interatomic distances of different atomic pairs are reduced at different rates with increasing pressure and the Cu-Cu pairs exhibit the highest percentage reduction. Between ambient pressure and 36.85 GPa, the atomic separation of the Cu-Cu pairs is reduced by ∼12% compared to ∼5% for Zr-Zr and Zr-Cu pairs. Such disproportional decrease in interatomic distance results in inhomogeneous atom reconfiguration in the short atomic range. With the increase of pressure, the Zr atoms move preferentially towards the Zr-Zr pairs, while the Cu atoms move preferentially towards the Cu-Cu pairs, creating inhomogeneous atom reconfiguration with positive short-range order coefficients of 0.0309 and 0.0464 for Zr-Zr and Cu-Cu respectively, but a negative value of −0.0464 for Zr-Cu pairs. Voronoi tessellation method was also used to study the evolution of the short-range atom packing versus pressure, elucidating the cause for the bimodal distribution of the bond angle distributions. The research sheds light on understanding of the atomic reconfiguration of equiatomic alloys under high pressure.
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Feb 2022
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I15-Extreme Conditions
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Abstract: The emergence of antimicrobial resistant strains bacteria and a decline in the discovery of new antibiotics has led to the idea of combining various antimicrobials to treat resistant strains and/or polymicrobial infections. Metal oxide-doped glasses have been extensively investigated for their antimicrobial potential; however to date, most experiments have focused on single metal species in isolation. The present study investigates the antimicrobial potential of sodium calcium phosphates (P2O5)50(Na2O)20(CaO)30–X(MO)X, where M is cobalt, copper, or zinc as single species. In addition, this work studied the effect of co-doping glasses containing two different metal ions (Co + Cu, Co + Zn, and Cu + Zn). The antimicrobial efficacy of all glasses was tested against Gram-positive (Staphylococcus aureus) and Gram-negative (Escherichia coli) bacterial strains, as well as a fungal strain (Candida albicans). Minimum inhibitory and bactericidal concentrations and time kill/synergy assays were used to assess the antimicrobial activity. An enhanced antimicrobial effect, at 5 mg/mL concentration, was exhibited by cobalt, copper, and zinc oxide glasses alone and in combinations. A synergistic antimicrobial effect was observed by Cu + Co and Cu + Zn against E. coli and Cu + Zn against S. aureus.
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Feb 2022
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I15-Extreme Conditions
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Diamond Proposal Number(s):
[21603]
Open Access
Abstract: The high-pressure behaviour of flexible zeolitic imidazolate frameworks (ZIFs) of the ZIF-62 family with the chemical composition M(im)2-x(bim)x is presented (M2+ = Zn2+, Co2+; im– = imidazolate; bim– = benzimidazolate, 0.02 ≤ x ≤ 0.37). High-pressure powder X-ray diffraction shows that the materials contract reversibly from an open pore (op) to a closed pore (cp) phase under a hydrostatic pressure of up to 4000 bar. Sequentially increasing the bim– fraction (x) reinforces the framework, leading to an increased threshold pressure for the op-to-cp phase transition, while the total volume contraction across the transition decreases. Most importantly, the typical discontinuous op-to-cp transition (first order) changes to an unusual continuous transition (second order) for x ≥ 0.35. This allows finetuning the void volume and the pore size of the material continuously by adjusting the pressure, thus opening new possibilities for MOFs in pressure-switchable devices, membranes, and actuators.
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Feb 2022
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I15-Extreme Conditions
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Diamond Proposal Number(s):
[20883]
Open Access
Abstract: Using synchrotron X-ray total scattering and empirical potential structure refinement modelling, we studied systematically in operando condition the disorder-to-order local atomic structure transition in a pure Al and a dilute Al-0.4Sc alloy melt in the temperature range from 690 °C to 657 °C. In the liquid state, icosahedral short-range ordered Sc-centred Al polyhedrons form and most of them with Al coordination number of 10–12. As the melt is cooled to the semisolid state, the most Sc-centred polyhedrons become more connected atom clusters via vertex, edge and face-sharing. These polyhedrons exhibit partially icosahedral and partially face-centred-cubic symmetry. The medium-range ordered Sc-centred clusters with face-sharing are proved to be the “precursors” of the L12 Al3Sc primary phases in the liquid-solid coexisting state.
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Jan 2022
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I15-Extreme Conditions
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Nanci Prado
Sabalisck
,
Gerardo
Gil-De-Cos
,
Cristina
Gonzalez-Silgo
,
Candelaria
Guzman-Afonso
,
Victor
Lavin
,
Juan Javier
Lopez-Solano
,
Isabel Teresa
Martín-Mateos
,
Lourdes
Mestres
,
Andres
Mujica
,
David
Santamaria-Perez
,
Manuel
Eulalio Torres
,
Xavier
Vendrell
Diamond Proposal Number(s):
[8617]
Abstract: X-ray powder diffraction experiments at high pressures combining conventional sources and synchrotron radiation, together with theoretical simulations have allowed us to study the anomalous compression of the entire α-
R
E
2
(
WO
4
)
3
(
RE
= La-Ho) family with modulated scheelite structure (α phase). The investigated class of materials is of great interest due to their peculiar structural behavior with temperature and pressure, which is highly sought after for specialized high-tech applications. Experimental data were analyzed using full-profile refinements and were complemented with computational methods based on density functional theory (DFT) total energy calculations for a subset of the samples investigated. An unusual change in the compression curves of the lattice parameters
a
,
c
, and β was observed in both the experiments and theoretical simulations. In particular, in all the studied compounds the lattice parameter
a
decreased with pressure to a minimum value and then increased upon further compression. Pressure evolution of the experimental x-ray diffraction (XRD) patterns and cell parameters is correlated with the ionic radius of the rare earth element: (1) the lighter La-Nd tungstates underwent two phase transitions, and both transition pressures decreased as the rare earth's ionic radius increased. The XRD patterns of the first high pressure phase could be indexed with propagation vectors parallel to the
a
axis (tripling the unit cell). At higher pressures, the lattice parameters for the second phase (referred to as the preamorphous phase) showed little variation with pressure. (2) The heavier tungstates, from Sm to Dy, undergo a transition to the preamorphous phase without any intermediate phase. The reversibility of both phase transitions was investigated. DFT calculations support this unusual response of the crystal structures under pressure and shed light on the structural mechanism of negative linear compressibility (NLC) and the resulting softening. The pressure dependence of the structural modifications is related to tilting, along with small elongation and alignment, of the
WO
2
−
4
tetrahedrons. These changes correlate with those in the alternating RE…RE…RE chains and blocks of cationic vacancies arranged along the
a
axis. Possible stacking defects, which emerge between them, helped to explain this anomalous compression and the pressure induced amorphization. Such mechanisms were compared with other ferroelastic families of molybdates, niobates, vanadates, and other compounds with similar structural motifs classified as having “hinge frames.”
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Dec 2021
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