High-pressure Angle-dispersive X-ray Research Articles

Structural evolvement of 1-methyl-3,4,5-trinitropyrazole at high pressure

Explosives, a type of energetic material (EM), face a high-pressure environment in the detonation process or under shock conditions. Determining their high-pressure behavior is critical to their explosion and safety. 1-Methyl-3,4,5-trinitropyrazole (MTNP), a carrier of melt-cast explosives, exhibits the potential for replacing trinitrotoluene (TNT). However, there is limited knowledge about its structural evolvement at high pressure. Using a diamond anvil cell (DAC), this study investigated the structural variation of MTNP through in situ high-pressure synchrotron angle-dispersive X-ray diffraction (ADXRD) experiments and Raman measurements. As evidenced by the results, MTNP underwent phase transition at 8.7 GPa and amorphization at 15.3 GPa due to high pressure. Through the analysis of first-principles calculations and Raman spectra, this study proposed the mechanisms behind the changes in MTNP at high pressure. Furthermore, this study systematically explored the structural evolvement of MTNP and the evolution of its weak intermolecular interactions at high pressure, gaining further understanding of MTNP's detonation and safety.

In situ high-pressure pair distribution function measurement of liquid and glass by using 100keV pink beam.

Understanding the pressure-induced structural changes in liquids and amorphous materials is fundamental in a wide range of scientific fields. However, experimental investigation of the structure of liquid and amorphous material under in situ high-pressure conditions is still limited due to the experimental difficulties. In particular, the range of the momentum transfer (Q) in the structure factor [S(Q)] measurement under high-pressure conditions has been limited at relatively low Q, which makes it difficult to conduct detailed structural analysis of liquid and amorphous material. Here, we show the in situ high-pressure pair distribution function measurement of liquid and glass by using the 100keV pink beam. Structures of liquids and glasses are measured under in situ high-pressure conditions in the Paris-Edinburgh press by high-energy x-ray diffraction measurement using a double-slit collimation setup with a point detector. The experiment enables us to measure S(Q) of GeO2 and SiO2 glasses and liquid Ge at a wide range of Q up to 20-29 Å-1 under in situ high-pressure and high-temperature conditions, which is almost two times larger than that of the conventional high-pressure angle-dispersive x-ray diffraction measurement. The high-pressure experimental S(Q) precisely determined at a wide range of Q opens the way to investigate detailed structural features of liquids and amorphous materials under in situ high-pressure and high-temperature conditions, as well as ambient pressure study.

High-pressure structural behavior and elastic properties of Ce2In and Ce3In: A combined in situ synchrotron X-ray diffraction and density functional theory study

Across the cerium (Ce)-indium (In) binary phase diagram, there are five line compounds including Ce3In, Ce2In, Ce3In5, CeIn2 and CeIn3. So far, CeIn3 is the only compound whose high-pressure structural behavior and elastic properties have been studied in detail. In this work, we investigated the compression behavior of Ce3In and Ce2In at pressures up to 26.2 GPa using in situ high-pressure angle dispersive synchrotron powder X-ray diffraction (XRD). Our results indicate that Ce3In retains its Cu3Au-type structure in the pressure range investigated, whereas Ce2In undergoes a phase transformation from the Ni2In-type structure to an unidentified phase at ∼4.6 GPa. Unit-cell parameters as a function of pressure were obtained by Rietveld analysis of XRD data. Unit cell volumes were fitted to a second order Birch-Murnaghan equation of state (EOS). The experimentally determined bulk moduli (K0) of the two cerium indides are 50 ± 3 GPa for Ce3In and 39.2 ± 1.6 GPa for Ce2In. The zero-pressure compressibilites of the a-axis (βa,0) for Ce3In is 6.67 (±0.36) × 10–3 GPa–1 and of the a- and c-axis for Ce2In are βa,0 = 8.85 (±0.39) × 10−3 GPa−1 and βc,0 = 9.26 (±0.51) × 10−3 GPa−1, respectively. These results are in general agreement with those calculated by density functional theory (DFT + U) and open-source machine learning algorithms.

Pressure-Induced Structural Phase Transition of Co-Doped SnO2 Nanocrystals

Co-doped SnO2 nanocrystals (with a particle size of 10 nm) with a tetragonal rutile-type (space group P42/mnm) structure have been investigated for their use in in situ high-pressure synchrotron angle dispersive powder X-ray diffraction up to 20.9 GPa and at an ambient temperature. An analysis of experimental results based on Rietveld refinements suggests that rutile-type Co-doped SnO2 undergoes a structural phase transition at 14.2 GPa to an orthorhombic CaCl2-type phase (space group Pnnm), with no phase coexistence during the phase transition. No further phase transition is observed until 20.9 GPa, which is the highest pressure covered by the experiments. The low-pressure and high-pressure phases are related via a group/subgroup relationship. However, a discontinuous change in the unit-cell volume is detected at the phase transition; thus, the phase transition can be classified as a first-order type. Upon decompression, the transition has been found to be reversible. The results are compared with previous high-pressure studies on doped and un-doped SnO2. The compressibility of different phases will be discussed.

Shear stress induced phase transitions of cubic Eu2O3 under non-hydrostatic pressures

Pressure-induced phase transitions in cubic Eu2O3 subjected to non-hydrostatic conditions have been studied by in situ high-pressure synchrotron angle dispersive x-ray diffraction and Raman scattering measurements up to 30.1 and 43.8 GPa, respectively. Both x-ray diffraction and Raman spectroscopy results indicate that the pressure-induced transition routines of cubic Eu2O3 depend on the nature of stress loading. In contrast to our previous high-pressure studies of cubic Eu2O3 under hydrostatic pressure, where cubic Eu2O3 transforms directly into a hexagonal structure, the x-ray diffraction data show that cubic Eu2O3 begins to transform into the monoclinic phase at a non-hydrostatic pressure of about 4.3 GPa, while the monoclinic to hexagonal phase transition is initiated at about 6.4 GPa. These phase transitions have also been confirmed by Raman spectroscopy; the hexagonal phase is stable up to at least 43.8 GPa; and the material decompressed from high pressures is composed of a monoclinic phase, showing that the cubic Eu2O3 to monoclinic phase transition is irreversible due to the constructive nature. Pressure coefficients of Raman peaks and Grüneisen mode parameters of cubic, monoclinic, and hexagonal phases followed under pressure were determined. Furthermore, this study provides evidence for the shear stress-induced cubic to monoclinic phase transition in cubic Eu2O3 and the corresponding mechanism.

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.

Engineering ZnO with Cu doping to lower the transition pressure: Experimental and theoretical investigations

Zinc Oxide (ZnO) is an n-type wide bandgap semiconductor. Doping of different elements in ZnO potentially affects its structural, optical and electronic properties. We have carried out high pressure angle dispersive x-ray diffraction and Raman scattering studies on Zn0.99Cu0.01O. We observed the substantial lowering of the transition pressure threshold from the wurtzite to rock salt phase compared to pristine ZnO. Experimental findings are also supported through computational data from density functional theory simulations. The charge transfer from a Cu atom in ZnO may be responsible for the reduction in the transition pressure threshold.

Fluorescence-based monitoring of the pressure-induced aggregation microenvironment evolution for an AIEgen under multiple excitation channels

The development of organic solid-state luminescent materials, especially those sensitive to aggregation microenvironment, is critical for their applications in devices such as pressure-sensitive elements, sensors, and photoelectric devices. However, it still faces certain challenges and a deep understanding of the corresponding internal mechanisms is required. Here, we put forward an unconventional strategy to explore the pressure-induced evolution of the aggregation microenvironment, involving changes in molecular conformation, stacking mode, and intermolecular interaction, by monitoring the emission under multiple excitation channels based on a luminogen with aggregation-induced emission characteristics of di(p-methoxylphenyl)dibenzofulvene. Under three excitation wavelengths, the distinct emission behaviors have been interestingly observed to reveal the pressure-induced structural evolution, well consistent with the results from ultraviolet-visible absorption, high-pressure angle-dispersive X-ray diffraction, and infrared studies, which have rarely been reported before. This finding provides important insights into the design of organic solid luminescent materials and greatly promotes the development of stimulus-responsive luminescent materials.

The coupling of lattice-strain and phonon induced order-disorder phase transition in layered LiGaO2

Recently, order-disorder phase transition has been considered as an emerging method to engineer bandgap in semiconductors. In this work, we uncovered that the coupling of lattice strain and phonon dominates the pressure-induced order-disorder phase transition in α-LiGaO2 via in situ high-pressure angle dispersive X-ray diffraction (ADXRD) and Raman scattering experiments, with the aids of first-principles calculations. Upon compression, ADXRD experiments show that the anisotropic compression of the layered structure leads to the order-disorder phase transition. Combining with lattice dynamics, we observed that the transition begins at about 16 GPa based on coherent nucleation induced by the oxygen atoms opposite motion that is the result of the coupling of lattice strain and phonon mode A1g. This result further shows that the disorder in crystal can be a correlated behavior and controlling the disorder in crystal can be used to create materials with new or improved functionality.

Insights into the Bond Behavior and Mechanical Properties of Hafnium Carbide under High Pressure and High Temperature.

Hafnium carbide (HfC) is a potential candidate of ultrahigh-temperature ceramics (UHTCs) and has attracted significantly widespread interest in recent years. Here, we have synthesized high-purity HfC samples with NaCl-type structure by using a high-pressure solid-solid reaction. The structural stability, equation of state, plastic deformation, yield strength, and bonding properties under high pressure are investigated by a series of in situ high-pressure synchrotron-radiation angle-dispersive X-ray diffraction experiments combined with first-principles calculations. The yield strength of HfC (∼18 GPa) is obtained from analyzing the plastic deformation behavior under high pressure. In addition, we have successfully prepared bulk HfC ceramics with high density using a high-pressure and high-temperature method. The synthesized sample possesses a desirable Vickers hardness of 24.2 GPa and an excellent fracture toughness of 5.0 MPa·m1/2. The present results offer insights into the achievable application of HfC ceramics under extreme conditions and provide a powerful guide for the further design and synthesis of other high-performance UHTCs.

Suppression of magnetic ordering in Fe-deficient Fe3−xGeTe2 from application of pressure

Two-dimensional van der Waals magnets with multiple functionalities are becoming increasingly important for emerging technologies in spintronics and valleytronics. Application of external pressure is one method to cleanly explore the underlying physical mechanisms of the intrinsic magnetism. In this paper, the magnetic, electronic, and structural properties of van der Waals-layered, Fe-deficient ${\mathrm{Fe}}_{3\ensuremath{-}x}\mathrm{Ge}{\mathrm{Te}}_{2}$ are investigated. Magnetotransport measurements show a monotonic decrease in the Curie temperature $({T}_{C})$ and the magnetic moment with increasing pressure up to 13.9 GPa. The electrical resistance of ${\mathrm{Fe}}_{3\ensuremath{-}x}\mathrm{Ge}{\mathrm{Te}}_{2}$ shows a change from metallic to a seemingly nonmetallic behavior with increasing pressure. High-pressure angle dispersive powder x-ray diffraction shows a monotonic compression of the unit cell and a reduction of the volume by $\ensuremath{\sim}25%$ with no evidence of structural phase changes up to 29.4(4) GPa. We suggest that the decrease in the ${T}_{C}$ due to pressure results from increased intralayer coupling and delocalization that leads to a change in the exchange interaction.

High-pressure X-ray diffraction study, optical properties, and applications of CaMoO4:Eu3+ nanosheets in white LEDs

Red-emitting CaMoO4:Eu3+ nanosheets were prepared via a facile precipitation method at room temperature without any organic additives. The structural characterization indicates that these nanosheets are single-crystalline with an average diameter of ∼1.657 μm and a thickness of ∼10 nm. We investigated the high-pressure behaviors of bulk CaMoO4 and CaMoO4:Eu3+ nanosheets by in situ high-pressure synchrotron angle-dispersive X-ray diffraction (XRD) technique at room temperature with the pressures up to 35.0 and 40.1 GPa, respectively. Two pressure-induced phase transitions were observed for both bulk CaMoO4 and CaMoO4:Eu3+ nanosheets in the range of studied pressure. The two high-pressure phases were analyzed and identified to be monoclinic structures with I2/a and P21/n space group, respectively. The compressibility of the CaMoO4 is highly non-isotropic, and the c-axis is more compressible than a-axis and b-axis. Furthermore, the compressibility of the c-axis of CaMoO4:Eu3+ nanosheets is greater than that of bulk CaMoO4. On the release of pressure from 35.0 to 40.1 GPa, the initial phase is recovered, implying that the observed structural modifications are reversible. CaMoO4: Eu3+ sheets also show higher luminescence efficiency that of bulk CaMoO4: Eu3+, which is reflected in higher Ω2 value. The continuous shift of emission peaks indicates the changes in local symmetry of Eu3+ with pressure, which is consistent with our high-pressure XRD study. The potential applications of CaMoO4:Eu3+ nanosheets were explored and our findings show that white light with excellent color quality (CRI>90) and a high LER up to 345 lm/W could be achieved.

Evolutions of structural and optical properties of lead-free double perovskite Cs<sub>2</sub>TeCl<sub>6</sub> under high pressure

In recent years, organic-inorganic hybrid perovskite materials have been widely used in solar cells, photodetectors, and light-emitting diodes due to their advantages such as high light absorption coefficient, good carrier mobility, and long carrier diffusion length. However, the high toxicity of lead and poor stability still restrict the application and promotion of such materials. The lead-free double perovskite material derived from the concept of “heterovalent substitution”, while maintaining the high symmetrical structure of perovskite, avoids using the toxic lead elements, which has the advantages of environmental friendly, stable structure, and suitable band gap. At present, the limited research on lead-free double perovskite materials still leaves a big room to researchers, and such a limited research seriously restricts the development and promotion of such materials. Therefore, the relationship between the structure and performance of lead-free double perovskite materials needs further exploring in order to provide theoretical basis for the practical application of such materials. Here in this work, the lead-free double perovskite material Cs<sub>2</sub>TeCl<sub>6</sub> is prepared by the solution method. The crystal structure and optical properties of the lead-free double perovskite Cs<sub>2</sub>TeCl<sub>6</sub> under high pressure are investigated by using diamond anvil cell combined with <i>in-situ</i> high-pressure angle-dispersive X-ray diffraction and ultraviolet-visible absorption technology. The results show that the crystal structure of Cs<sub>2</sub>TeCl<sub>6</sub> is not changed within the experimental pressure range of 0－50.0 GPa, and the structural symmetry of <i>Fm-</i>3<i>m</i> is still maintained, indicating the sample has good stability. The lattice constant and volume of Cs<sub>2</sub>TeCl<sub>6</sub> gradually decrease within the pressure range of 0－50.0 GPa. The volume and pressure of Cs<sub>2</sub>TeCl<sub>6</sub> are fitted using the third-order Birch-Mumaghan equation of state, the bulk elastic modulus is obtained to be <i>B</i><sub>0</sub> = (18.77 ± 2.88) GPa. The smaller bulk elastic modulus indicates that the lead-free double perovskite material Cs<sub>2</sub>TeCl<sub>6</sub> has higher compressibility. The optical band gap of Cs<sub>2</sub>TeCl<sub>6</sub> is 2.68(3) eV at 1 atm and its optical band gap gradually decreases with the increase of pressure, which is related to the shrinkage of octahedral [TeCl<sub>6</sub>]<sup>2–</sup> under high pressure. The calculation results show that the Cs<sub>2</sub>TeCl<sub>6</sub> possesses an indirect band gap, the valence band maximum is mainly composed of Cl 3p orbits, and the conduction band minimum is mainly composed of Te 5p and Cl 3p orbits. After the pressure is completely relieved, Cs<sub>2</sub>TeCl<sub>6</sub> returns to the initial state. The above conclusions further deepen the understanding of the crystal structure and optical properties of lead-free double perovskite Cs<sub>2</sub>TeCl<sub>6</sub>, and provide a theoretical basis for designing and optimizing the lead-free double perovskite materials.

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.

Pressure-Induced Emission (PIE) of One-Dimensional Organic Tin Bromide Perovskites.

Low-dimensional halide perovskites easily suffer from the structural distortion related to significant quantum confinement effects. Organic tin bromide perovskite C4N2H14SnBr4 is a unique one-dimensional (1D) structure in which the edge sharing octahedral tin bromide chains [SnBr42-]∞ are embraced by the organic cations C4N2H142+ to form the bulk assembly of core-shell quantum wires. Some unusual phenomena under high pressure are accordingly expected. Here, an intriguing pressure-induced emission (PIE) in C4N2H14SnBr4 was successfully achieved by means of a diamond anvil cell. The observed PIE is greatly associated with the large distortion of [SnBr6]4- octahedral motifs resulting from a structural phase transition, which can be corroborated by in situ high-pressure photoluminescence, absorption, and angle-dispersive X-ray diffraction spectra. The distorted [SnBr6]4- octahedra would accordingly facilitate the radiative recombination of self-trapped excitons (STEs) by lifting the activation energy of detrapping of self-trapped states. First-principles calculations indicate that the enhanced transition dipole moment and the increased binding energy of STEs are highly responsible for the remarkable PIE. This work will improve the potential applications in the fields of pressure sensors, trademark security, and information storage.

Spectroscopic properties and martensitic phase transition of Y4Al2O9:Ce single crystals under high pressure

High pressure studies of monoclinic yttrium aluminum oxide single crystals (Y4Al2O9 -YAM) doped with Ce3+ ions grown by micro-pulling-down method are reported. The results of absorption measurements in the mid-infrared prove the existence of four different sites in which Ce3+ ions substitute Y ions, in accordance with the crystallographic structure of YAM. The lowest 5d level of Ce3+ is located very close to the bottom of the conduction band for two of four Ce3+ related centers at ambient pressure, which results in strong temperature quenching of their luminescence. Two other Ce3+ centers do not emit at ambient pressure since their 5d levels are resonant with the conduction band. Application of high pressure above 11 GPa restores their luminescence. Consequences of such energy structure of various Ce3+ sites in YAM for the Dorenbos theory are discussed. The bandgap energy of YAM is found to be 5.93 eV, which is the smallest out of the three yttrium aluminum oxides. High-pressure synchrotron angle dispersive x-ray diffraction and Raman scattering measurements identify a phase transition occurring at pressures between 8 and 11 GPa, which has martensitic character. The second phase transition to another structure (likely with hexagonal symmetry) occurs at a pressure around 16 GPa.

High-pressure angle-dispersive X-ray diffraction study of mechanically alloyed SnSe2

The effect of pressure on mechanically alloyed trigonal nanostructured SnSe2 (n-SnSe2) was studied by in situ angle-dispersive X-ray diffraction up to 25.8 GPa. The pressure dependence of lattice parameters and unit cell volume was investigated. By fitting the lattice parameters and unit cell volume to a third-order Birch–Murnaghan equation of state for several values of the applied pressure, the bulk modulus B0, its first derivative B′, and the linear moduli along the a- and c-axes were determined. The effect of pressure on the z coordinate of site 2d occupied by Se atoms was investigated using pair distribution function analysis. The results were compared with experimental and theoretical studies of SnS2 and SnSe2 reported in the literature.

Near Zero Area Compressibility in a Perovskite-Like Metal-Organic Frameworks [C(NH2)3][Cd(HCOO)3

Materials with zero area compressibility (ZAC) can keep their crystal uncompressed in two specific directions upon uniform compression. High-pressure angle-dispersive X-ray powder diffraction (ADXRD) experiments reveal a ZAC phenomenon in the ab-plane in crystal of a formate-based perovskite, [C(NH2)3][Cd(HCOO)3]. The ZAC behavior is ascribed to the unique rhombohedral [Cd(HCOO)3]- frameworks and confirmed by density functional theory (DFT) calculations. For the first time, a near ZAC single material is explicitly reported. This study opens up an exciting research field on pressure-resistant materials. We anticipate more ZAC materials to be discovered in the following explorations under the inspiration of this work.

Strengthening effects of interstitial nitrogen on rhenium

Introducing interstitial nitrogen atoms into the rhenium lattices is accepted for enhancing the mechanical and thermal properties of the metal. Here, we present an experimental study on the strengthening effects of interstitial nitrogen in rhenium on bulk modulus B0 and elastic shear constant C44 by comparing the difference in the compression and vibration behaviors between Re3N and Re in the in situ high pressure angle dispersive X-ray diffraction and high-pressure Raman scattering. The incorporation of interstitial N atoms introduces the covalent bonding and the special Z-type structure along the c-axis, which caused the bulk modulus B0 and elastic shear constant C44 increase by 14% and 15%, and the incompressibility of the c-axis is obviously enhanced. In addition, this work well explains the strengthening effects of interstitial N atoms on mechanical and vibrational properties.

High-Pressure Synthesis of CeOCl Crystals and Investigation of Their Photoluminescence and Compressibility Properties

The well-crystallized mixed anions compound cerium oxychloride (CeOCl) was successfully synthesized by a high-pressure solid-state metathesis reaction. The photoluminescence experiment shows that the CeOCl, with a band gap of ∼3.05 eV, has good violet-blue emission properties. And first-principles calculations of the band structures show that CeOCl is an indirect (direct) band gap semiconductor for the spin-up (spin-down) branch. This suggests that the CeOCl can be expected to be a semiconductor material. In addition, in situ high-pressure angle-dispersive X-ray diffraction experiment reveals that the bulk modulus of CeOCl is 52.8(8) GPa, which is close to our first-principles calculations, giving that B0 = 47.6(5) GPa.