High-pressure X-ray Diffraction Data Research Articles

Crystal structure of the incommensurate modulated high-pressure phase of the potassium guaninate monohydrate.

The crystal structure of the incommensurate modulated phase of potassium guaninate monohydrate has been solved on the basis of high-pressure single-crystal X-ray diffraction data. The modulated structure was described as a `mosaic' sequence of three different local configurations of two neighbouring guaninate rings. In contrast to known examples of incommensurate modulated organic compounds, the modulation functions of all atoms are discontinuous. This is the first example of the experimental detection of an incommensurate modulated crystal structure that can be modelled using the special `soliton mode' modulation function proposed by Aramburu et al. [(1995), J. Phys. Condens. Matter, 7, 6187-6196].

Negative linear compressibility and strong enhancement of emission in Eu[Ag(CN)2]3·3H2O under pressure.

The framework material Eu[Ag(CN)2]3·3H2O exhibits a negative linear compressibility (NLC) of -4.2(1) TPa-1 over the largest pressure range yet observed (0-8.2 GPa). High-pressure single-crystal X-ray diffraction data show that the rapid contraction of the Kagome silver layers under compression causes the wine-rack lattice to expand along the c-axis. The hydrogen bonds between the water molecules and the main frameworks constrain the structural deformation under pressure and eventually a weak NLC effect generated. Furthermore, we found that the pressure-induced emission intensity increases almost 800-fold at 4.0 GPa, followed by a gradual decrease and disappearance at 8.1 GPa. Under compression, high pressure significantly tunes the triplet level positions near the Eu3+ ions, and horizontal displacement between a quenching excited state and the excited levels of Eu3+ facilitates the energy transfer process to the 5D0 excited state and limits the nonradiative corssover at elevated pressures, thus increasing the emission intensity. In addition, we observe a gradual band gap reduction with increasing pressure, and the sample could not be returned to the initial state after the pressure was completely released. By controlling the structural flexibility, we observe a coupled NLC and pressure-induced strong enhancement of the emission properties of Eu[Ag(CN)2]3·3H2O, which provides a new route for the design of new optical devices with intriguing luminescence properties under extreme environments.

High-Pressure Experimental and DFT Structural Studies of Aurichalcite Mineral

We report on high-pressure angle-dispersive synchrotron X-ray diffraction data of a natural Zn3.78(2)Cu1.22(2)(CO3)2(OH)6 aurichalcite mineral up to 7.6 GPa and ab initio total energy calculations of the aurichalcite structure with three different Zn-Cu stoichiometries (Zn:Cu ratios = 10:0, 8:2 and 6:4). A monoclinic-to-triclinic displacive second-order phase transition was found experimentally at 3 GPa. The experimental bulk modulus of the initial P21/m aurichalcite is B0 = 66(2) GPa, with a first-pressure derivative of B0′ = 9(2). A comparison with other basic copper and zinc carbonates shows that this B0 value is considerably larger than those of malachite and azurite. This relative incompressibility occurs despite the fact that aurichalcite features a layered structure due to the number of directed hydrogen bonds between carbonate groups and the cation-centered oxygen polyhedra forming complex sheets. The existence of different bond types and polyhedral compressibilities entails a certain anisotropic compression, with axial compressibilities κa0 = 3.79(5)·10−3 GPa−1, κb0 = 5.44(9)·10−3 GPa−1 and κc0 = 4.61(9)·10−3 GPa−1. Additional density-functional theory calculations on the C2/m hydrozincite-type structure with different Zn:Cu compositional ratios shows that the aurichalcite structure is energetically more stable than the hydrozincite one for compositions of Zn:Cu = 10:0, 8:2 and 6:4 at room pressure. The pure Zn aurichalcite phase, however, was predicted to transform into hydrozincite at 18 GPa, which suggests that the experimentally observed hydrozincite structure is a metastable phase.

Tracking structural phase transitions via single crystal x-ray diffraction at extreme conditions: advantages of extremely brilliant source

Highly brilliant synchrotron source is indispensable to track pressure-induced phenomena in confined crystalline samples in megabar range. In this article, a number of experimental variables affecting the quality high-pressure single-crystal x-ray diffraction data is discussed. An overview of the recent advancements in x-ray diffraction techniques at extreme conditions, in the frame of European Synchrotron Radiation Facility (ESRF)- Extremely Bright Source (EBS), is presented. Particularly, ID15b and ID27 beamlines have profited from the source upgrade, allowing for measurements of a few-micron crystals in megabar range. In case of ID27, a whole new beamline has been devised, including installation of double-multilayer mirrors and double crystal monochromator and construction of custom-made experimental stations. Two case studies from ID27 and ID15b are presented. Hypervalent CsI3 crystals, studied up to 24 GPa, have shown a series of phase transitions: Pnma → P-3c1→ Pm-3 n. First transition leads to formation of orthogonal linear iodine chains made of I3 -. Transformation to the cubic phase at around 21.7 GPa leads to equalization of interatomic I–I distances and formation of homoleptic In m- chains. The second study investigates elastic properties and structure of jadarite, which undergoes isosymmetric phase transition around 16.6 GPa. Despite a few-micron crystal size, twinning and dramatic loss of crystal quality, associated with pressure-induced phase transitions, crystal structures of both compounds have been determined in a straightforward matter, thanks to the recent developments within ESRF-EBS.

Pressure-induced metallization in the absence of a structural transition in the layered ferromagnetic insulator Cr2Ge2Te6

We report the crystallographic and electrical transport properties of single crystals of the ferromagnetic two-dimensional (2D) material ${\mathrm{Cr}}_{2}{\mathrm{Ge}}_{2}{\mathrm{Te}}_{6}$ under high pressure. In contrast to previous studies, our high-pressure single-crystal x-ray diffraction under hydrostatic conditions shows prominent anisotropic compressibility in the layered structure of the crystalline $R\overline{3}$ phase of ${\mathrm{Cr}}_{2}{\mathrm{Ge}}_{2}{\mathrm{Te}}_{6}$ without any structural phase transitions up to 20 GPa. Our data confirm a distinct and irreversible crystalline-amorphous transformation in ${\mathrm{Cr}}_{2}{\mathrm{Ge}}_{2}{\mathrm{Te}}_{6}$. The loss of crystallinity starts at 20 GPa; however, the crystalline phase and amorphous state coexist even at the maximum pressure of 31.2 GPa. High-pressure powder x-ray diffraction data and electrical resistivity measurements of ${\mathrm{Cr}}_{2}{\mathrm{Ge}}_{2}{\mathrm{Te}}_{6}$ using NaCl as the pressure-transmitting medium reveal an insulator-to-metal transition in the absence of a phase transition at \ensuremath{\sim}3.9 GPa; at a considerably lower pressure than the previously reported (7--14 GPa). Density functional theory calculations demonstrate the density of states around the Fermi level are primarily dominated by Cr $3d$ and Te $5p$ states. Hence the large reduction of Cr-Te bond lengths within the ${\mathrm{CrTe}}_{6}$ octahedra under compression is most likely responsible for the band-gap closure. This study clarifies that the phase stability and onset of metallization pressure in the ${\mathrm{Cr}}_{2}{\mathrm{Ge}}_{2}{\mathrm{Te}}_{6}$ sample are sensitive to the hydrostatic environments and demonstrates how pressure can be used to tune the physical properties of 2D ferromagnetic compounds.

Magnetism in four-layered Aurivillius Bi[formula omitted]FeTi[formula omitted]O15 at high pressures

We report the structural and magnetic properties of four-layer Aurivillius compound Bi5FeTi3O15 (BFTO) at high hydrostatic pressure conditions. The high-pressure x-ray diffraction (XRD) data does not explicitly show structural phase transitions with pressure, however the observed changes in lattice parameters indicate structural modifications at different pressure values. In the initial pressure region values (up to 2.2 GPa), the lattice parameters a- and b- are nearly equal implying a quasi-tetragonal structure, however as the pressure increases a- and b- diverges apart and exhibits complete orthorhombic phase at pressure values of about ≥8 GPa. Principal component analysis (PCA) of high pressure Raman measurements point out an evident change in the local structure at about 5.5 GPa indicating that the evolution of the local structure under applied pressure seems to not follow crystallographic changes (long range order). Nuclear forward scattering (NFS) measurements reveal the development of magnetic ordering in BFTO at 5K with high pressures. A progressive increase in magnetic order is observed with increase in pressure at 5 K. Further, NFS measurements carried out at constant pressure (6.4 GPa) and different temperatures indicate that the developed magnetism disappears at higher temperatures (20 K). It is attempted to explain these observations in terms of the observed structural parameter variation with pressure.

Structure–compressibility correlation among MoBx

Molybdenum forms a large number of borides with various stoichiometries. In this paper the trends in the compressibility behaviour among MoBx (x: 0.5, 1, 2 and 3) were investigated. High-pressure structural stability studies on MoB3 were carried out up to a pressure of 40 GPa using a Mao–Bell-type diamond anvil cell. The hexagonal structure remained stable up to 40 GPa. High-pressure X-ray diffraction data yielded a bulk modulus of 254 GPa and were in good agreement with computed bulk moduli of 258–295 GPa with various potentials. First-principles calculations were carried out to investigate the structural, elastic and mechanical properties of molybdenum borides based on generalized gradient approximation proposed by Perdew–Burke–Ernzerhof. The compressibility behaviour of MoBx (x = 0.5, 1, 2 and 3) showed parabolic trend and was explained in terms of electronic structure and mainly arose due to the partial charge density of boron.

Pressure-stabilized divalent ozonide CaO3 and its impact on Earth\u2019s oxygen cycles

High pressure can drastically alter chemical bonding and produce exotic compounds that defy conventional wisdom. Especially significant are compounds pertaining to oxygen cycles inside Earth, which hold key to understanding major geological events that impact the environment essential to life on Earth. Here we report the discovery of pressure-stabilized divalent ozonide CaO3 crystal that exhibits intriguing bonding and oxidation states with profound geological implications. Our computational study identifies a crystalline phase of CaO3 by reaction of CaO and O2 at high pressure and high temperature conditions; ensuing experiments synthesize this rare compound under compression in a diamond anvil cell with laser heating. High-pressure x-ray diffraction data show that CaO3 crystal forms at 35 GPa and persists down to 20 GPa on decompression. Analysis of charge states reveals a formal oxidation state of −2 for ozone anions in CaO3. These findings unravel the ozonide chemistry at high pressure and offer insights for elucidating prominent seismic anomalies and oxygen cycles in Earth’s interior. We further predict multiple reactions producing CaO3 by geologically abundant mineral precursors at various depths in Earth’s mantle.

Compressibility and thermoelasticity of CrN

ABSTRACT We report experimental determination of compressibility and thermoelasticity for CrN based on in situ high pressure/high temperature synchrotron x-ray diffraction measurements. The pressure-induced cubic-to-orthorhombic phase transition is observed at ∼ 5 GPa in high-quality CrN samples synthesized using a high pressure reaction route. Equation of state, bulk modulus and axial compressibility of this material are obtained by analysis of high pressure x-ray diffraction data collected at room temperature. Both cubic and orthorhombic phases have a similar bulk modulus value of 257 (5) and 262 (6) GPa, respectively. For orthorhombic CrN, the b-axis has the most axial incompressibility, which should be associated with magnetic properties. In addition, the isothermal equation of states is also determined at different temperatures of 300, 400, 600, 800, 1000, and 1200 K, respectively. Some of the important thermoelastic properties of cubic CrN are thus derived, including temperature derivative of bulk modulus and volumetric thermal expansivity where a 0 = 1.95 (16) × 10−5 K−1 and a 1 = 4.39 (3) × 10−9 K−1.

Effect of Alkali and Trivalent Metal Ions on the High-Pressure Phase Transition of [C2H5NH3]MI 0.5MIII 0.5(HCOO)3 (MI = Na, K and MIII = Cr, Al) Heterometallic Perovskites.

We report the high-pressure behavior of two perovskite-like metal formate frameworks with the ethylammonium cation (EtAKCr and EtANaAl) and compare them to previously reported data for EtANaCr. High-pressure single-crystal X-ray diffraction and Raman data for EtAKCr show the occurrence of two high-pressure phase transitions observed at 0.75(16) and 2.4(2) GPa. The first phase transition involves strong compression and distortion of the KO6 subnetwork followed by rearrangement of the −CH2CH3 groups from the ethylammonium cations, while the second involves octahedral tilting to further reduce pore volume, accompanied by further configurational changes of the alkyl chains. Both transitions retain the ambient P21/n symmetry. We also correlate and discuss the influence of structural properties (distortion parameters, bulk modulus, tolerance factors, and compressibility) and parameters calculated by using density functional theory (vibrational entropy, site-projected phonon density of states, and hydrogen bonding energy) on the occurrence and properties of structural phase transitions observed in this class of metal formates.

Pressure-Induced Emission (PIE) and Phase Transition of a Two-dimensional Halide Double Perovskite (BA)4 AgBiBr8 (BA=CH3 (CH2 )3 NH3 + ).

Two-dimensional (2D) halide perovskites have attracted significant attention due to their compositional flexibility and electronic diversity. Understanding the structure-property relationships in 2D double perovskites is essential for their development for optoelectronic applications. In this work, we observed the emergence of pressure-induced emission (PIE) at 2.5 GPa with a broad emission band and large Stokes shift from initially nonfluorescent (BA)4 AgBiBr8 (BA=CH3 (CH2 )3 NH3 + ). The emission intensity increased significantly upon further compression up to 8.2 GPa. Moreover, the band gap narrowed from the starting 2.61 eV to 2.19 eV at 25.0 GPa accompanied by a color change from light yellow to dark yellow. Analysis of combined in situ high-pressure photoluminescence, absorption, and angle-dispersive X-ray diffraction data indicates that the observed PIE can be attributed to the emission from self-trapped excitons. This coincides with [AgBr6 ]5- and [BiBr6 ]3- inter-octahedral tilting which cause a structural phase transition. High-pressure study on (BA)4 AgBiBr8 sheds light on the relationship between the structure and optical properties that may improve the material's potential applications in the fields of pressure sensing, information storage and trademark security.

Structural stability of MoB up to 25 GPa: experiment and computation

In this work we report both experimental and computational study on the structural stability of MoB under pressure. The single phase MoB with tetragonal structure (I41/amd) having lattice parameters a = 3.109(2) Ǻ and c = 16.936(7) Ǻ was studied using a Mao-Bell type diamond anvil cell (DAC) to collect high pressure x-ray diffraction (HPXRD) data in angle dispersive x-ray mode up to a pressure of ∼25 GPa. The tetragonal structure remains stable up to 25 GPa. The a-axis shows lower compressibility than the c-axis. The anisotropy behaviour in the compressibility is discussed taking cue from the bond alignment in the structure. Compressibility behaviour of MoB is also compared to WB with regard to their electronic structure and charge distribution. The charge density plots as a function of pressure reveal strong covalent bond along a-axis and weak covalent bond between Mo-B. The high pressure XRD data yields a bulk modulus of 311 GPa which agrees well with the computed value of ∼304 GPa.

The High Pressure Behavior of Galenobismutite, PbBi2S4: A Synchrotron Single Crystal X-ray Diffraction Study

High-pressure single-crystal synchrotron X-ray diffraction data for galenobismutite, PbBi2S4 collected up to 20.9 GPa, were fitted by a third-order Birch-Murnaghan equation of state, as suggested by a FE-fE plot, yielding V0 = 697.4(8) Å3, K0 = 51(1) GPa and K’ = 5.0(2). The axial moduli were M0a = 115(7) GPa and Ma’ = 28(2) for the a axis, M0b = 162(3) GPa and Mb’ = 8(3) for the b axis, M0c = 142(8) GPa and Mc’ = 26(2) for the c axis, with refined values of a0, b0, c0 equal to 11.791(7) Å, 14.540(6) Å 4.076(3) Å, respectively, and a ratio equal to M0a:M0b:M0c = 1.55:1:1.79. The main structural changes on compression were the M2 and M3 (occupied by Bi, Pb) movements toward the centers of their respective trigonal prism bodies and M3 changes towards CN8. The M1 site, occupied solely by Bi, regularizes the octahedral form with CN6. The eccentricities of all cation sites decreased with compression testifying for a decrease in stereochemical expression of lone electron pairs. Galenobismutite is isostructural with calcium ferrite CaFe2O4, the suggested high pressure structure can host Na and Al in the lower mantle. The study indicates that pressure enables the incorporation of other elements in this structure, increasing its potential significance for mantle mineralogy.

Boron monosulfide: Equation of state and pressure-induced phase transition

Quasi-hydrostatic compression of rhombohedral boron monosulfide (r-BS) has been studied up to 50 GPa at room temperature using diamond-anvil cells and angle-dispersive synchrotron X-ray diffraction. A fit of the experimental P–V data to the Vinet equation of state yields the bulk modulus B0 of 42.2(1.4) GPa and its first pressure derivative B0′ of 7.6(2) that are in excellent agreement with our ab initio calculations. Formation of a new high-pressure phase of boron monosulfide (hp-BS) has been observed above 35 GPa. According to ab initio evolutionary crystal structure predictions combined with Rietveld refinement of high-pressure X-ray diffraction data, the structure of hp-BS has trigonal symmetry and belongs to the space group P-3m1. As it follows from the electron density of state calculations, the phase transformation is accompanied by an insulator-metal transition.

Structural Behavior of Natural Silicate–Carbonate Spurrite Mineral, Ca5(SiO4)2(CO3), under High-Pressure, High-Temperature Conditions

We report on high-pressure and high-temperature angle-dispersive synchrotron X-ray diffraction and high-pressure Raman data up to 27 GPa and 700 K for natural silicate carbonate Ca5(SiO4)2(CO3) spurrite mineral. No phase transition was found in the studied P-T range. The room-temperature bulk modulus of spurrite using Ne as the pressure-transmitting medium is B0 = 77(1) GPa with a first-pressure derivative of B0' = 5.9(2). The structure compression is highly anisotropic, the b axis being approximately 30% more compressible than the a and c axes. The volumetric thermal expansivity value around 8 GPa was estimated to be 4.1(3) × 10-5 K-1. A comparison with intimately related minerals CaCO3 calcite and aragonite and β-Ca2SiO4 larnite shows that, as the composition and structural features of spurrite suggest, its compressibility and thermal expansivity lie between those of the silicate and carbonate end members. The crystal chemistry and thermodynamic properties of spurrite are discussed.

LaB Work Function and Structural Stability under High Pressure**Supported by the National Natural Science Foundation of China under Grant Nos 11274030 and 11474281.

The work functions of the (110) and (100) surfaces of LaB are determined from ambient pressure to 39.1 GPa. The work function of the (110) surface slowly decreases but that of the (100) surface remains at a relatively constant value. To determine the reason for this difference, the electron density distribution (EDD) is determined from high-pressure single-crystal x-ray diffraction data by the maximum entropy method. The EDD results show that the chemical bond properties in LaB play a key role. The structural stability of LaB under high pressure is also investigated by single-crystal x-ray diffraction. In this study, no structural or electronic phase transition is observed from ambient pressure to 39.1 GPa.

High-pressure high-temperature phase diagram of organic crystal paracetamol

High-pressure high-temperature (HPHT) Raman spectroscopy studies have been performed on the organic crystal paracetamol in a diamond anvil cell utilizing boron-doped heating diamond anvil. Isobaric measurements were conducted at pressures up to 8.5 GPa and temperature up to 520 K in five different experiments. Solid state phase transitions from monoclinic Form I → orthorhombic Form II were observed at various pressures and temperatures as well as transitions from Form II → unknown Form IV. The melting temperature for paracetamol was observed to increase with increasing pressures to 8.5 GPa. This new data is combined with previous ambient temperature high-pressure Raman and x-ray diffraction data to create the first HPHT phase diagram of paracetamol.

Crystal behavior of potassium bromate under compression.

We report on high-pressure angle-dispersive X-ray diffraction data up to 15 GPa and ab initio total-energy calculations up to 242 GPa for KBrO3. No phase transition was found below 15 Pa in contrast to previously reported data. Its experimental bulk modulus in the quasi-hydrostatic regime is B0 = 18.8 (9) GPa with a bulk modulus pressure derivative B'0 = 8.2 (4). However, according to our ab initio calculations, KBrO3 significantly reduces its rhombohedral distortion via small cooperative movements of the atoms and the structure progressively approaches the cubic symmetry, where the KBr subarray would adopt a topology similar to that of the corresponding B2-type bromide. This rearrangement of atoms is directly related to the Buerger's mechanism of the B1-B2 phase transition for halides, confirming that cations (second neighbors) do not arrange in an arbitrary way. The O atoms forming the [BrO3] pyramidal units move smoothly with pressure to the center of the [K8] cube faces, where electron localization function calculations present their maxima in other B2-type compounds, eventually adopting the perovskite-type structure at P ≃ 152 GPa. Our data on KBrO3 has been compared with chemically substituted isostructural halates, providing new insights on the compressibility of this family of compounds.

Strength of polycrystalline niobium from high-pressure x-ray diffraction data: A comparison of results from line-width and line-shift analyses

High purity polycrystalline niobium was compressed in a diamond anvil cell (DAC) without any pressure transmitting medium and the pressure was increased in steps of ∼5 GPa to the highest pressure of ∼40 GPa. The diffraction pattern was recorded after each pressure increment using angle-dispersive mode with the conventional diffraction geometry, wherein the primary x-ray beam is parallel to the load axis of the DAC. The strength of niobium as function of pressure was determined using the line-width and line-shift analyses. Both eY and 2eY, where Y is the aggregate Young's modulus and e is the strain determined from the line-width analysis, have been used as the measure of strength in earlier studies. In this study, it is eY that agrees with the strength determined from the line-shift analysis of the radial diffraction data as well as the data from the conventional diffraction geometry. These results have been discussed and compared with a similar observation made earlier on strength of diamond. This study highlights the ambiguity that presently exists in choosing eY or 2eY as a measure of strength while attempting to estimate the strength from the diffraction line width analysis.

Crystal Structure of Sinhalite MgAlBO4 under High Pressure

We report on high-pressure angle-dispersive X-ray diffraction data up to 27 GPa for natural MgAlBO4 sinhalite mineral and ab initio total energy calculations. The experimental bulk modulus of sinhalite is B0 = 171(3) GPa with a first-pressure derivative of B0′ = 4.2(3). A comparison with other olivine-type compounds shows that the value for B0 is 27% larger than that of Mg2SiO4 forsterite and 29% smaller than that of Al2BeO4 chrysoberyl. These differences are interpreted, on the basis of our ab initio calculations, in terms of the relative incompressibility of Al–O bonds in AlO6 octahedra (with a calculated bulk modulus of 250(1) GPa) as compared to Mg–O bonds in MgO6 octahedra (with a calculated bulk modulus of 130(1) GPa). The spatial cation distribution in the Pbnm orthorhombic unit cell and different polyhedral compressibilities entails a strong anisotropic compression comparable to that of forsterite. The axial compressibilities are 1.06(2) × 10–3, 2.17(2) × 10–3, and 1.30(3) × 10–3 GPa–1 for a, b, and c axes, respectively. The crystal chemistry of sinhalite under compression is compared to that of other olivine-like compounds. Compressibility trends and possible high-pressure phases are discussed.