Angle-dispersive Synchrotron X-ray Diffraction Research Articles

Vibration-Dependent Dual-Phosphorescent Cu4 Nanocluster with Remarkable Piezochromic Behavior.

The dual emission (DE) characteristics of atomically precise copper nanoclusters (Cu NCs) are of significant theoretical and practical interest. Despite this, the underlying mechanism driving DE in Cu NCs remains elusive, primarily due to the complexities of excited state processes. Herein, a novel [Cu4(PPh3)4(C≡C-p-NH2C6H4)3]PF6 (Cu4) NC, shielded by alkynyl and exhibiting DE, was synthesized. Hydrostatic pressure was applied to Cu4, for the first time, to investigate the mechanism of DE. With increasing pressure, the higher-energy emission peak of Cu4 gradually disappeared, leaving the lower-energy emission peak as the dominant emission. Additionally, the Cu4 crystal exhibited notable piezochromism transitioning from cyan to orange. Angle-dispersive synchrotron X-ray diffraction results revealed that the reduced inter-cluster distances under pressure brought the peripheral ligands closer, leading to the formation of new C-H···N and N-H···N hydrogen bonds in Cu4. It is proposed that these strengthened hydrogen bond interactions limit the ligands´ vibration, resulting in the vanishing of the higher-energy peak. In situ high-pressure Raman and vibrationally resolved emission spectra demonstrated that the benzene ring C=C stretching vibration is the structural source of the DE in Cu4.

High-pressure study of synthesized α-Bi2O3/NiBi3 nanostructured composite: In-situ synchrotron XRD measurements, DFT calculations and PDF approach

We investigated a nanostructured composite of α-Bi2O3/NiBi3, which was synthesized through high-energy milling, under high-pressure conditions of up to 30 GPa. To track its structural changes, we employed in-situ synchrotron angle-dispersive X-ray diffraction measurements in conjunction with density functional theory calculations. Crystallographic information was derived using the Rietveld method and DFT computations. Additionally, we examined the chemical short-range order using pair distribution functions and determined the compressibility parameters through the Birch-Murnaghan equation of state.We explored the high-pressure behavior of a nanostructured composite of α-Bi2O3/NiBi3, applying pressures up to 30 GPa. The composite sample, synthesized by mechanical alloying, underwent thorough structural characterization by X-ray diffraction, high-resolution transmission electron microscopy and Raman spectroscopy. The sample's response to applied pressure was studied by analyzing crystallographic data obtained from in-situ synchrotron angle-dispersive X-ray diffraction measurements and density functional theory calculations. Crystallographic information from experiments was refined using the Rietveld method. Additionally, chemical short-range order was examined using pair distribution functions, and compressibility parameters were determined via the Birch-Murnaghan equation of state. This investigation into the high-pressure behavior of NiBi3 provides valuable insights for future studies and potential applications of similar materials in extreme pressure environments.

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.

Pressure tuning reverse martensitic transformation in the Mn0.9Co0.1NiGe half-Heusler alloy

Here we investigate the structural properties of the Mn0.9Co0.1NiGe half-Heusler alloys under pressure up to 12 GPa by Synchrotron angle-dispersive x-ray diffraction (XRD). At room temperature and pressure, the compound exhibits only the hexagonal NiIn2-type structure. Lowering the temperature to 100 K at ambient pressure induces an almost complete martensitic phase transformation to the orthorhombic TiNiSi-type structure. With increasing pressure, the stable orthorhombic phase gradually undergoes a reverse martensitic transformation. The hexagonal phase reaches 85% of the sample when applying 12 GPa of pressure at T = 100 K. We further evaluated the bulk modulus of both hexagonal and orthorhombic phases and found similar values (123.1 ± 5.9 GPa for hexagonal and 102.8 ± 4.2 GPa for orthorhombic). Also, we show that the lattice contraction induced is anisotropic. Moreover, the high-pressure hexagonal phase shows a volumetric thermal contraction coefficient α v ∼ −8.9(1) × 10−5K−1 when temperature increases from 100 to 160 K, evidencing a significant negative thermal expansion (NTE) effect. Overall, our results demonstrate that the reverse martensitic transition presented on Mn0.9Co0.1NiGe induced either by pressure or temperature is related to the anisotropic contraction of the crystalline arrangement, which should also play a crucial role in driving the magnetic phase transitions in this system.

Pressure-induced phase transition in cubic Yb2O3 and phase transition enthalpies

The high pressure structural evolution of cubic Yb2O3 has been studied using in situ synchrotron angle dispersive x-ray diffraction in combination with diamond anvil cell techniques up to 44.1 GPa. The XRD measurements revealed an irreversible reconstructive phase transition from cubic to monoclinic Yb2O3 at 11.2 GPa and extending up to 28.1 GPa with ∼8.1% volume collapse and a subsequent reversible displacive transition from monoclinic to hexagonal phase starting at 22.7 GPa. The monoclinic phase coexists with the hexagonal phase up to 44.1 GPa. After pressure releases, the hexagonal Yb2O3 reverts to the monoclinic structure. The second-order Birch–Murnaghan equation of state fit to the pressure–volume data yields a bulk modulus of 201 (4), 187 (6), and 200 (4) GPa for the cubic, monoclinic, and hexagonal phases, respectively. Furthermore, the effects of the hydrostatic pressure state on the diffraction patterns, bulk modulus, and onset transition pressure of Yb2O3 under high pressure have been discussed. It is concluded that the bulk modulus of the cubic Ln2O3 phase increases with decreasing cation radius due to lanthanide contraction. Another important work in this study is the determination of the enthalpies of the cubic to monoclinic and monoclinic to hexagonal phase transitions of Yb2O3 of 37.0 and 17.4 kJ/mol, respectively, based on the basic thermodynamic equations and using the onset transition pressures and corresponding volume changes obtained from high pressure XRD experiments.

High-Pressure Vibrational and Structural Studies of the Chemically Engineered Ferroelectric Phase of Sodium Niobate

Pure NaNbO3 has an antiferroelectric phase at ambient pressure. The structural behaviour of the chemically engineered ferroelectric phase of sodium niobate, NNBT05: [(0.95) NaNbO3-(0.05) BaTiO3], under high-pressure has been studied using Raman scattering and angle-dispersive synchrotron X-ray diffraction techniques. At pressure > 1 GPa, noticeable changes in the Raman spectra can be seen in the low wavenumber modes (150–300 cm−1). Large changes in the positions and intensities of the Raman bands as a function of pressure provide evidence for structural phase transition. The results indicate significant changes in the bond-lengths and the orientation of the NbO6 octahedra at ~1 GPa, and a transition to the paraelectric phase at ~5 GPa, which are at lower pressures than previously found in pure NaNbO3. The powder X-ray diffraction pattern shows an appreciable change in the peak profile in terms of position and width on increasing pressure. The pressure dependences of the structural parameters show that the response of the lattice parameters to pressure is strongly anisotropic. By fitting the pressure–volume data using the Birch–Murnaghan equation of state, the isothermal bulk modulus was estimated. The experimental results suggest that on doping BaTiO3 in NaNbO3, the bulk modulus increases. The bulk modulus of NNBT05 has been estimated to be 164.5 GPa, which is fairly close to 157.5 GPa, as previously observed in NaNbO3.

Pressure-induced structural transition of pyrochlore Tm2Sn2O7

The geometrically frustrated pyrochlore Tm2Sn2O7 is an insulator with a slight trigonal lattice distortion at ambient conditions. High pressure was applied to this system to investigate the responses of structural evolution. In-situ angle-dispersive synchrotron X-ray diffraction and Raman spectroscopy analyses have been performed on Tm2Sn2O7 up to 52.6(1) GPa and 62.1(1) GPa, respectively. It was found that Tm2Sn2O7 transformed from the cubic (Fd3̅m) structure to the orthorhombic (Pnma) structure around 36.7(1) GPa. The phase transition was mainly induced by the increased cation disorder upon compression, which efficiently modified its surrounding coordination environment. After releasing pressure, both experimental results revealed that the structural phase transition was reversible.

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.

The pressure-induced structural transformation of La2S3

As a fundamental thermodynamic parameter, pressure can cause matters to produce new phases with unique physical properties. In this paper, the pressure-induced behavior of La2S3 has been investigated in depth by in-situ high pressure synchrotron angle dispersive X-ray diffraction (ADXRD), and the pressure is up to 26 GPa. We find the conventional La2S3 which was stable at ambient pressure, was destabilized with the application of pressure and decomposed into La3S4 and LaS2 at 13.4 GPa. This is the first time that the high pressure decomposition of La2S3 has been found in the experiments. The La2S3 possesses the lowest formation enthalpy at atmospheric pressure, enthalpy change increases with the pressure increasing, leading to the decomposition of La2S3. The high pressure inhibits the ability of S atoms to accept electrons and promotes the polymerization of S atoms to form shared electron pairs, brings in the change of S–S bonding modes, and also further leads to the change of structural. The study of pressure relief experiment shows that the pressure induced decomposition in La2S3 is an irreversible phase transition. The different radial direction has the different compression effects under pressure, the initial structure decays rapidly driven by pressure. With the pressure rising, the decay rate becomes gentle. The volume expansion of La3S4 and LaS2 may be due to some defects, and the smaller the volume, the greater the bulk modulus. This work provides a strong support for the theoretical research results and is expected to provide guidance for the experiment study of the physical properties and structural characteristics of La–S system and other rare earth sulfur compounds.

Crystallographic structural variations in nano-crystalline Sc2O3 under pressure

The present manuscript reports high-pressure investigations on nano-crystalline Scandium Oxide (Sc2O3) through synchrotron angle dispersive x-ray diffraction technique (ADXRD) up to a pressure of ∼35.4 GPa using a diamond-anvil cell (DAC). The sample, having a cubic bixbyite structure at ambient conditions, underwent substantial changes in crystallographic parameters under the application of external pressure, while exhibiting phase stability i.e. does not undergo any structural phase transition up to 35.4 GPa. The lattice parameters and the unit cell volume decrease significantly with an increase in pressure, revealing the compressible nature of the crystal structure. The pressure-volume data is fitted using the third-order Birch-Murnaghan equation of state to calculate the bulk modulus and its first derivative, which yields zero pressure bulk modulus of 217(35) GPa, with = 12(4) and the corresponding ambient volume per unit molecule comes out to be 59.18(18) Å3.

Effects of High Pressure on the Bandgap and the d–d Crystal Field Transitions in Wolframite NiWO4

The pressure effects on the optical and structural properties of NiWO4 have been studied experimentally and theoretically. The fundamental bandgap decreases with a pressure coefficient of −12.0 ± 0.2 meV/GPa. Meanwhile, the Ni2+ d–d transition energies increase at a rate of 7.4–14.8 meV/GPa. Therefore, the energy differences between the fundamental band and the Ni2+ d–d transition bands gradually decrease under pressure, which is beneficial to improve its optical performance. These optical phenomena are associated with structural variations. The shrinkage of the WO6 octahedron enhances the hybridization between the W 5d and O 2p orbitals, resulting in bandgap reduction. The pressure-induced enhancement of the NiO6 octahedral symmetry increases the crystal field splitting, thereby yielding increases in the Ni2+ d–d intraband transition energies. Besides, a pressure-induced structural phase transition is also observed around 20.0 GPa by both angle-dispersive synchrotron X-ray diffraction (ADXRD) and Raman experiments. This study provides valuable insight into the electron–lattice coupling of NiWO4 under compression and an effective way to modulate the electronic structure and optical properties of isomorphic wolframite materials.

Structural correlation to enhanced magnetodielectric properties of Pr-doped polycrystalline Gd0.55Pr0.45MnO3 at low temperatures

The effect of improved dielectric properties in the presence of an applied magnetic field is discussed in polycrystalline Gd0.55Pr0.45MnO3 complemented by the structural and magnetic properties. Enhanced dielectric permittivity and low dielectric loss represent the strongly field-dependent dielectric behaviour of the sample. The structural characterizations using synchrotron angle dispersive X-ray diffraction confirm the orthorhombic symmetry of the polycrystalline sample with the Pnma space group in the temperature range from 300 K to 50 K. There is no structural transition observed at lower temperatures down to 50 K; however the Mn- O octahedral distortion is slightly reduced. The magneto-dielectric measurements were performed in the frequency range 500 Hz–1 MHz and temperature range 8 K–300 K both with and without external magnetic field (up to 7 Tesla), which shows the high dielectric constant. The magnetic study shows the negative magnetization and high coercivity in Gd0.55Pr0.45MnO3 at low temperatures due to competition in between spin ordering of Mn and Gd + Pr magnetic lattice. The MnOMn bond angle study indicates the A-type antiferromagnetic structure of the material at lower temperature.

Equations of State and Crystal Structures of KCaPO4, KSrPO4, and K2Ce(PO4)2 under High Pressure: Discovery of a New Polymorph of KCaPO4.

We have studied by means of angle-dispersive powder synchrotron X-ray diffraction the structural behavior of KCaPO4, SrKPO4, and K2Ce(PO4)2 under high pressure up to 26, 25, and 22 GPa, respectively. For KCaPO4, we have also accurately determined the crystal structure under ambient conditions, which differs from the structure previously reported. Arguments supporting our structural determination will be discussed. We have found that KCaPO4 undergoes a reversible phase transition. The onset of the transition is at 5.6 GPa. It involves a symmetry decrease. The low-pressure phase is described by space group P3̅m1 and the high-pressure phase by space group Pnma. For KSrPO4 and K2Ce(PO4)2, no evidence of phase transitions has been found up to the highest pressure covered by the experiments. For the three compounds, the linear compressibility for the different crystallographic axes and the pressure-volume equation of states are reported and compared with those of other phosphates. The three studied compounds are among the most compressible phosphates. The results of the study improve the knowledge about the high-pressure behavior of complex phosphates.

Experimental and theoretical revelation of a unique band topology in Sb[formula omitted]Te[formula omitted] topological insulator by substitution of Cu—A high pressure study

TI Sb1.9Cu0.1Te3 is an ideal platform for investigating such semiconducting to metal transition under extreme conditions. The unusual softening of two newly M1, M2 phonon modes combined with the sudden collapse in bond length, angle of succession, intralayer distance and the direct observation of band gap closure from theoretical density functional theory calculation validates a unique metal transition. To the best of our knowledge, the metallic transition pressure in the present observation is the lowest amongst the A2B3 TI family of compounds. This distinctive transition is stimulated by the p-d hybridization which is the concomitant effect of Cu and applied pressure. We also establish structural and vibrational anomalies from pressure induced angle dispersive synchrotron x-ray diffraction and Raman spectra of the bulk that signify changes in electronic topology of the Fermi surface. Our experimental observations on bulk corroborates an ETT (∼2.5 GPa) and 3 structural transitions in the present system.

Vacancy infilling during the crystallization of Fe-deficient hematite: An in situ synchrotron X-ray diffraction study of non-classical crystal growth

Abstract The crystallization of hematite from precursor ferrihydrite was studied using time-resolved, angle-dispersive synchrotron X-ray diffraction in aqueous solutions at pH 10 and 11 and at temperatures ranging from 80 to 170 °C. Rietveld analyses revealed a non-classical crystallization pathway involving vacancy infilling by Fe as defective hematite nanocrystals evolved. At 90 °C and pH 11, incipient hematite particles exhibited an Fe site occupancy as low as 0.68(2), and after 30 min, Fe occupancy plateaued at 0.84(1), achieving a metastable steady state with a composition corresponding to “hydrohematite.” During crystal growth, unit-cell volume increased with an increase in Fe occupancy. The increase in Fe occupancy in hydrohematite was accomplished by deprotonation, resulting in a shortening of the long Fe-O(H) bonds and decreased distortion of the octahedral sites. Once the occupancy stabilized, the unit-cell volume contracted following further nanoparticle growth. Our study documented various synthetic routes to the formation of “hydrohematite” with an Fe vacancy of 10–20 mol% in the final product. The structure refined for synthetic hydrohematite at 90 °C and pH 11 closely matched that of natural hydrohematite from Salisbury, Connecticut, with a refined Fe occupancy of 0.83(2). Dry heating this natural hydrohematite generated anhydrous, stoichiometric hematite, again by continuous infilling of vacancies. The transformation initiated at 150 °C and was complete at 700 °C, and it was accompanied by the formation of a minor amorphous phase that served as a reservoir for Fe during the inoculation of the defective crystalline phase.

Thermal expansion and compressibility of calcium scandate CaSc2O4

By using in-situ synchrotron angle-dispersive X-ray diffraction measurements, the thermal expansion and compressibility of orthorhombic CaSc2O4 were investigated up to 1173 K at ambient pressure and up to 15.9 GPa at room temperature, respectively. No phase transformation was observed in this study. The thermal expansion coefficients of CaSc2O4 were determined to be 4.17(3) × 10−5 K−1, 1.60(1) × 10−5 K−1, 1.18(1) × 10−5 K−1 and 1.39(1) × 10−5 K−1 for the V, a-, b- and c-axis, respectively. The isothermal bulk modulus of CaSc2O4 was obtained as 153.8(50) GPa with its first pressure derivative of 6.5(9). The axial compressibility was estimated to be 123(3), 177(4) and 242(11) GPa for the a-, b- and c-axis, respectively. Both the thermal expansion and compressibility of CaSc2O4 show axial anisotropy. The heat capacities (Cv and Cp) of CaSc2O4 was estimated by using a Kieffer model with Raman spectroscopy data and present experimental results. The standard entropy (S2980) and Debye temperature (θD) of CaSc2O4 were also calculated.

Hematite-goethite ratios at pH 2–13 and 25–170 °C: A time-resolved synchrotron X-ray diffraction study

Iron (oxyhydr)oxides are sensitive indicators of pH, Eh, temperature, microbial activity, and climate conditions in the Critical Zone. The most ubiquitous and environmentally significant iron oxides in most soils are two-line ferrihydrite, goethite, and hematite. Here we present a comprehensive study of the transformation of two-line ferrihydrite to hematite and goethite over a wide range of temperature (25–170 °C) and initial pH (2−13) conditions through ex situ batch and in situ synchrotron X-ray diffraction (XRD) experiments.Within the high time resolution of our experiments, goethite and hematite nucleated nearly simultaneously from ferrihydrite in nearly equal concentrations by mass. Hematite increased in abundance relative to goethite until a steady-state ratio was achieved, and both phases ceased growth on the depletion of ferrihydrite. Higher temperatures and lower water activities favored hematite formation at all pH values studied. In both our batch and our time-resolved, angle-dispersive synchrotron X-ray diffraction experiments, hematite was favored relative to goethite at an initial pH of 3 to 5. In contrast, goethite preferentially formed in neutral (initial pH 7–8) and highly alkaline conditions (initial pH ≥ 11). Surprisingly, mildly alkaline conditions (initial pH 9–11) induced the precipitation of a highly Fe-deficient (Feocc = ~0.80–0.90) variety of hematite known as “hydrohematite” in greater concentrations than goethite. Our results are useful for the application of hematite-goethite ratios as paleoclimate proxies for soil and sediment systems with low pH buffering capacities.

Structural evolution and bandgap modulation of layered β-GeSe2 single crystal under high pressure

Germanium diselenide (GeSe2) is a promising candidate for electronic devices because of its unique crystal structure and optoelectronic properties. However, the evolution of lattice and electronic structure of β-GeSe2 at high pressure is still uncertain. Here we prepared high-quality β-GeSe2 single crystals by chemical vapor transfer (CVT) technique and performed systematic experimental studies on the evolution of lattice structure and bandgap of β-GeSe2 under pressure. High-precision high-pressure ultra low frequency (ULF) Raman scattering and synchrotron angle-dispersive x-ray diffraction (ADXRD) measurements support that no structural phase transition exists under high pressure up to 13.80 GPa, but the structure of β-GeSe2 turns into a disordered state near 6.91 GPa and gradually becomes amorphous forming an irreversibly amorphous crystal at 13.80 GPa. Two Raman modes keep softening abnormally upon pressure. The bandgap of β-GeSe2 reduced linearly from 2.59 eV to 1.65 eV under pressure with a detectable narrowing of 36.5%, and the sample under pressure performs the piezochromism phenomenon. The bandgap after decompression is smaller than that in the atmospheric pressure environment, which is caused by incomplete recrystallization. These results enrich the insight into the structural and optical properties of β-GeSe2 and demonstrate the potential of pressure in modulating the material properties of two-dimensional (2D) Ge-based binary material.

High-Pressure Studies of Trimethylsilane Azide by Raman Scattering and Synchrotron X-ray Diffraction.

We have reported the high-pressure behavior of energetic material trimethylsilane azide ((CH3)3SiN3, TMSiN3) by in situ Raman scattering and synchrotron angle-dispersive X-ray diffraction (ADXRD) measurements in diamond anvil cells with a pressure up to ∼40 GPa at ambient temperature. The analyses of Raman spectra showed two liquid-liquid phase transitions at 0.13 and 7.9 GPa. The XRD results verified that TMSiN3 remained in a liquid state throughout the phase transitions. In the pressure range of 0.13-2.6 GPa, the distortion of the Si-C3 bond and the shortening of the bond between azide group and silicon atom lead to the first phase transition. The second transition is ascribed to the rotation of methyl group at 7.9 GPa. With further compression, the azide groups become increasingly asymmetric, and completely amorphous at 33.8 GPa. This paper is useful to understand the behavior of azide group and the molecular structural evolution of organic azide under high pressure. The unique high-pressure behavior of the azide group in TMSiN3 may be useful for improving in the formation of the polynitrogen compound with azides.