I15-1-X-ray Pair Distribution Function (XPDF)
|
Caleb J.
Bennett
,
Neha
Bura
,
Frederick P.
Marlton
,
Wen Liang
Tan
,
Tobias A.
Bird
,
Pablo
Botella
,
Peijie
Zhang
,
Benedito Donizeti
Botan-Neto
,
Jose Luis
Rodrigo Ramon
,
Catalin
Popescu
,
Frederico
Alabarse
,
Daniel
Errandonea
,
Brendan J.
Kennedy
Diamond Proposal Number(s):
[36827]
Abstract: A variable temperature X-ray total-scattering study of K2IrCl6 reveals compelling evidence for local symmetry breaking in this material. While the average crystal structure remains cubic down to 11 K, consistent with earlier reports, large anisotropic chloride displacements suggest short-range distortions of the IrCl6 octahedra. Pair distribution function analysis confirms that the local structure is better described by a monoclinic P21/n model featuring a mix of in-phase and out-of-phase octahedral tilts. This behavior mirrors observations in related K2MX6 halides, where thermally driven cubic-to-monoclinic transitions occur. High-pressure synchrotron measurements further reveal two structural transitions: cubic Fm3̅m to tetragonal P4/mnc at 12.0 GPa, and tetragonal to monoclinic P21/n at 15.1 GPa. Both transitions are reversible on decompression. Lattice parameter refinements indicate anisotropic compression with the bulk modulus increasing dramatically from 23 GPa in the cubic phase to 121 GPa in the monoclinic structure. These results demonstrate that both temperature reduction and applied pressure drive K2IrCl6 toward lower-symmetry phases. Overall, this study provides the first direct local-structure evidence of symmetry breaking in K2IrCl6 and highlights the complex interplay among pressure, temperature, and local structure in vacancy-ordered double perovskites.
|
Jan 2026
|
|
I15-Extreme Conditions
|
Diamond Proposal Number(s):
[40347]
Open Access
Abstract: We report a comparative high-pressure study of two fluorite-type rare-earth oxides with increasing configurational entropy, (CePr)O2–δ and (CePrLa)O2–δ. Synchrotron-based powder X-ray diffraction and Raman spectroscopy were carried out up to 30 and 20 GPa, respectively. Both compounds retain the cubic fluorite structure throughout the pressure range explored, although an anomaly is observed between 9 and 16 GPa, characterized by a compressibility plateau and changes in vibrational modes. This behavior is attributed to local lattice distortions and a progressive bond angle bending rather than abrupt phase transitions. In (CePrLa)O2−δ, the onset of amorphization is observed above 22 GPa, highlighting its reduced structural stability. The bulk modulus of both systems shows a slight decrease after the onset of the anomaly, suggesting subtle lattice softening. Raman spectroscopy reveals suppression of the F2g mode intensity with increasing cationic disorder, and under compression, partial reordering is evidenced by an increase in the RE–O mode intensity. Our results highlight the complex interplay between configurational entropy, cation size, and pressure in determining the structural stability and vibrational properties of rare-earth high-entropy oxides and provide insight into the mechanisms governing their resilience and local disorder under extreme conditions.
|
Dec 2025
|
|
I15-Extreme Conditions
|
A. L. J.
Pereira
,
J. A.
Sans
,
O.
Gomis
,
D.
Santamaria-Perez
,
S.
Ray
,
A.
Godoy
,
A. S.
Da Silva-Sobrinho
,
P.
Rodríguez-Hernández
,
A.
Muñoz
,
C.
Popescu
,
F. J.
Manjon
Diamond Proposal Number(s):
[6073]
Open Access
Abstract: We report a joint experimental and theoretical study of the structural and vibrational properties of C-type bulk Y2O3 under hydrostatic compression. The combination of high-pressure X-ray diffraction and Raman scattering experimental measurements with ab initio theoretical calculations on bulk Y2O3 allows us to confirm the cubic (C-type) - monoclinic (B-type) - trigonal (A-type) phase transition sequence on the upstroke and the trigonal-monoclinic phase transition on the downstroke. This result reconciles with the results already found in related rare-earth sesquioxides of cations with similar ionic radii as Y, such as Ho2O3 and Dy2O3, and ends with the controversy regarding the existence of the intermediate monoclinic phase between the cubic and trigonal phases in pure bulk Y2O3 on the upstroke. As a byproduct, the good agreement between experimental and calculated results allows us to use extensive theoretical data to discuss the structural and vibrational behavior of the three phases of Y2O3 under compression, thus allowing a more detailed understanding of the effect of pressure on rare-earth sesquioxides than previous studies.
|
May 2023
|
|
I19-Small Molecule Single Crystal Diffraction
|
Juan
Angel Sans
,
Francisco Javier
Manjon
,
André Luis
De Jesus Pereira
,
Javier
Ruiz-Fuertes
,
Catalin
Popescu
,
Alfonso
Muñoz
,
Plácida
Rodríguez-Hernández
,
Julio
Pellicer-Porres
,
Vanesa Paula
Cuenca-Gotor
,
Julia
Contreras-Garcia
,
Jordi
Ibañez
,
Virginia
Monteseguro
Diamond Proposal Number(s):
[22223]
Abstract: The structural, vibrational and electronic properties of the compressed β-Sb2O3 polymorph, a.k.a. mineral valentinite, have been investigated in a joint experimental and theoretical study up to 23 GPa. The compressibility of the lattice parameters, unit-cell volume and polyhedral unit volume as well as the behaviour of its Raman- and IR-active modes under compression have been interpreted on the basis of ab initio theoretical simulations. Valentinite shows an unusual compressibility up to 15 GPa with four different pressure ranges, whose critical pressures are 2, 4, and 10 GPa. The pressure dependence of the main structural units, the lack of soft phonons, and the electronic density charge topology address the changes at those critical pressures to isostructural phase transitions of degree higher than 2. In particular, the transitions at 2 and 4 GPa can be ascribed to the changes in the interaction between the stereochemically-active lone electron pairs of Sb atoms under compression. The changes observed above 10 GPa, characterized by a general softening of several Raman- and IR-active modes, point to a structural instability prior to the 1st-order transition occurring above 15 GPa. Above this pressure, a tentative new high-pressure phase (s.g. Pcc2) has been assigned by single-crystal and powder X-ray diffraction measurements.
|
Mar 2021
|
|
I15-Extreme Conditions
|
Diamond Proposal Number(s):
[8176, 9366]
Abstract: We report results from a series of diamond-anvil-cell synchrotron X-ray diffraction and largevolume- press experiments, and calculations, to investigate the phase diagram of commercial polycrystalline high-strength Ti-6Al-4V alloy in pressure-temperature space. Up to ~30 GPa and 886 K, Ti- 6Al-4V is found to be stable in the hexagonal-close-packed, or alpha phase. The effect of temperature on the volume expansion and compressibility of alpha-Ti-6Al-4V is modest. The martensitic alpha→omega (hexagonal) transition occurs at ~30 GPa, with both phases coexisting until further compression to ~38-40 GPa completes the transition to the omega phase. Between 300 K and 844 K the alpha→omega transition appears to be independent of temperature. Omega-Ti-6Al-4V is stable to ~91 GPa and 844 K, the highest combined pressure and temperature reached in these experiments. Pressure-volume-temperature equations-of-state for the alpha and omega phases of Ti- 6Al-4V are generated and found to be similar to pure Ti. A pronounced hysteresis is observed in the omega-Ti-6Al-4V on decompression, with the hexagonal structure reverting back to the alpha phase at pressures below ~9 GPa at room temperature, and at a higher pressure at elevated temperatures. Based on our data, we estimate the Ti-6Al-4V alpha-beta-omega triple point to occur at ~900 K and 30 GPa, in good agreement with our calculations.
|
Jan 2021
|
|
I15-Extreme Conditions
|
Juan A.
Sans
,
Rosario
Vilaplana
,
E. Lora
Da Silva
,
Catalin
Popescu
,
Vanesa P.
Cuenca-Gotor
,
Adrián
Andrada-Chacón
,
Javier
Sánchez-Benitez
,
Oscar
Gomis
,
André L. J.
Pereira
,
Plácida
Rodríguez-Hernández
,
Alfonso
Muñoz
,
Dominik
Daisenberger
,
Braulio
Garcia-Domene
,
Alfredo
Segura
,
Daniel
Errandonea
,
Ravhi S.
Kumar
,
Oliver
Oeckler
,
Philipp
Urban
,
Julia
Contreras-Garcia
,
Francisco J.
Manjón
Abstract: High pressure X-ray diffraction, Raman scattering, and electrical measurements, together with theoretical calculations, which include the analysis of the topological electron density and electronic localization function, evidence the presence of an isostructural phase transition around 2 GPa, a Fermi resonance around 3.5 GPa, and a pressure-induced decomposition of SnSb2Te4 into the high-pressure phases of its parent binary compounds (α-Sb2Te3 and SnTe) above 7 GPa. The internal polyhedral compressibility, the behavior of the Raman-active modes, the electrical behavior, and the nature of its different bonds under compression have been discussed and compared with their parent binary compounds and with related ternary materials. In this context, the Raman spectrum of SnSb2Te4 exhibits vibrational modes that are associated but forbidden in rocksalt-type SnTe; thus showing a novel way to experimentally observe the forbidden vibrational modes of some compounds. Here, some of the bonds are identified with metavalent bonding, which were already observed in their parent binary compounds. The behavior of SnSb2Te4 is framed within the extended orbital radii map of BA2Te4 compounds, so our results pave the way to understand the pressure behavior and stability ranges of other “natural van der Waals” compounds with similar stoichiometry.
|
Jul 2020
|
|
I15-Extreme Conditions
|
Diamond Proposal Number(s):
[9548, 7533]
Open Access
Abstract: We present an experimental study of the high-pressure, high-temperature behaviour of cerium up to $\sim$22 GPa and 820 K using angle-dispersive x-ray diffraction and external resistive heating. Studies above 820 K were prevented by chemical reactions between the samples and the diamond anvils of the pressure cells. We unambiguously measure the stability region of the orthorhombic \textit{oC}4 phase and find it reaches its apex at 7.1 GPa and 650 K. We locate the $\alpha$-\textit{cF}4 -- \textit{oC}4 -- \textit{tI}2 triple point at 6.1 GPa and 640 K, 1 GPa below the location of the apex of the \textit{oC}4 phase, and 1-2 GPa lower than previously reported. We find the $\alpha$-\textit{cF}4 $\rightarrow$ \textit{tI}2 phase boundary to have a positive gradient of 280 K/GPa, less steep than the 670 K/GPa reported previously, and find the \textit{oC}4 $\rightarrow$ \textit{tI}2 phase boundary to lie at higher temperatures than previously found. We also find variations as large as 2-3 GPa in the transition pressures at which the \textit{oC}4 $\rightarrow$ \textit{tI}2 transition takes place at a given temperature, the reasons for which remain unclear. Finally, we find no evidence that the $\alpha$-\textit{cF}4 $\rightarrow$ \textit{tI}2 is not second order at all temperatures up to 820 K.
|
Mar 2020
|
|
I15-Extreme Conditions
|
Diamond Proposal Number(s):
[23122]
Open Access
Abstract: The high-pressure and high-temperature structural and chemical stability of ruthenium has been investigated via synchrotron X-ray diffraction using a resistively heated diamond anvil cell. In the present experiment, ruthenium remains stable in the hcp phase up to 150 GPa and 960 K. The thermal equation of state has been determined based upon the data collected following four different isotherms. A quasi-hydrostatic equation of state at ambient temperature has also been characterized up to 150 GPa. The measured equation of state and structural parameters have been compared to the results of ab initio simulations performed with several exchange-correlation functionals. The agreement between theory and experiments is generally quite good. Phonon calculations were also carried out to show that hcp ruthenium is not only structurally but also dynamically stable up to extreme pressures. These calculations also allow the pressure dependence of the Raman-active E2g mode and the silent B1g mode of Ru to be determined.
|
Oct 2019
|
|
I15-Extreme Conditions
|
S.
Anzellini
,
D.
Errandonea
,
Simon
Macleod
,
P.
Botella
,
D.
Daisenberger
,
J. M.
De’ath
,
J.
Gonzalez-Platas
,
J.
Ibáñez
,
M. I.
Mcmahon
,
K. A.
Munro
,
C.
Popescu
,
J.
Ruiz-Fuertes
,
C. W.
Wilson
Diamond Proposal Number(s):
[15864]
Abstract: Resistively heated diamond-anvil cells have been used together with synchrotron x-ray diffraction to investigate the phase diagram of calcium up to 50 GPa and 800 K. The phase boundaries between the Ca-I (fcc), Ca-II (bcc), and Ca-III (simple cubic, sc) phases have been determined at these pressure-temperature conditions, and the ambient temperature equation of state has been generated. The equation of state parameters at ambient temperature have been determined from the experimental compression curve of the observed phases by using third-order Birch-Murnaghan and Vinet equations. A thermal equation of state was also determined for Ca-I and Ca-II by combining the room-temperature Birch-Murnaghan equation of state with a Berman-type thermal expansion model.
|
Aug 2018
|
|
I15-Extreme Conditions
|
Diamond Proposal Number(s):
[19846]
Open Access
Abstract: The phase diagram of zinc (Zn) has been explored up to 140 GPa and 6000 K, by combining optical observations, x-ray diffraction, and ab-initio calculations. In the pressure range covered by this study, Zn is found to retain a hexagonal close-packed (hcp) crystal symmetry up to the melting temperature. The known decrease of the axial ratio (c/a) of the hcp phase of Zn under compression is observed in x-ray diffraction experiments from 300 K up to the melting temperature. The pressure at which c/a reaches √3 (≈10 GPa) is not affected by temperature. When this ideal axial ratio is reached, we observed that single crystals of Zn, formed at high temperature, break into multiple poly-crystals. In addition, a noticeable change in the pressure dependence of c/a takes place at the same pressure. Both phenomena can be caused by an isomorphic second-order phase transition induced by pressure in Zn. The reported melt curve extends previous results from 24 to 135 GPa. The pressure dependence obtained for the melting temperature is accurately described by using a Simon–Glatzel equation. The determined melt curve agrees with previous low-pressure studies and with shock-wave experiments, with a melting temperature of 5060(30) K at 135 GPa. Finally, a thermal equation of state is reported, which at room-temperature agrees with the literature.
|
Jun 2018
|
|
