Pressure- and Temperature-Dependent Structural Stability of LLM-105

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C: Energy Conversion and Storage; Energy and Charge Transport

Pressure and Temperature Dependent Structural Stability of LLM-105 Crystal Zilong Xu, Hao Su, Xiaoqin Zhou, Xiangqi Wang, Junke Wang, Chan Gao, Xiaoyu Sun, Rucheng Dai, Zhongping Wang, Hongzhen Li, and Zengming Zhang J. Phys. Chem. C, Just Accepted Manuscript • DOI: 10.1021/acs.jpcc.8b10837 • Publication Date (Web): 27 Dec 2018 Downloaded from http://pubs.acs.org on January 3, 2019

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The Journal of Physical Chemistry

Pressure and Temperature Dependent Structural Stability of LLM-105 Crystal Zilong Xu1, Hao Su1, Xiaoqin Zhou2, Xiangqi wang1, Junke wang1, Chan Gao1, Xiaoyu Sun1, Rucheng Dai3*, Zhongping Wang3, Hongzhen Li2* and Zengming Zhang3, 4* 1. Department of Physics, University of Science and Technology of China, Hefei, Anhui 230026, China. 2. Insitute of Chemical Materials, China Academy of Engineering Physics，Mianyang, Sichuan 621900, China. 3. The Centre for Physical Experiments, University of Science and Technology of China,Hefei, Anhui 230026, China 4. Key Laboratory of Strongly-Coupled Quantum Matter Physics, Chinese Academy of Sciences, School of Physical Sciences, University of Science and Technology of China, Hefei, Anhui 230026, China Corresponding authors: (R.D) [email protected]; (H.L) [email protected]; and (Z.Z) [email protected]

Abstract New energetic material 2,6-diamino-3,5-dinitropyrazine-1-oxide (C4H4N6O5, LLM-105) maintains its structure stability under high pressure below 30 GPa at room temperature or in the temperature range from 513 K to 5 K with ambient pressure based on the high pressure or the cryogenic XRD patterns. One structural phase transition occurs at about 30 GPa and is confirmed by pressure-dependent Raman and infrared spectra. The structure of LLM-105 crystal shows anisotropic compressibility under pressure in the order βb >βa > βc and anisotropic thermal expansion in the order αb > αc ≈ αa. Debye temperature of 1225 K for this crystal is obtained based on the lattice parameters at different pressure or temperature. The experimental data reveal that the compression is a better path to reduce the volume of LLM-105 crystal comparing with cooling. Raman and infrared spectra at extreme conditions suggest that the structure stability is contributed to the stronger inter- and intra- molecule hydrogen bonding networks within LLM-105 crystal. The symmetric and asymmetric stretching modes of amino groups are coupled and it can improve the understanding of pressure evolution of LLM-105 crystal. The bond constants of amino groups with different pressure and temperature are also obtained.

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Introduction Energetic material 2,6-diamino-3,5-dinitropyrazine-1-oxide (C4H4N6O5 Lawrence Livermore Molecule No. 105, LLM-105) is attracting considerable attention due to its low sensitivity and high energy density.1-9 The higher nitrogen content and density (1.913 g/cm3) results in its detonation velocity larger than 7500 m/s and detonation pressure higher than 30 GPa. The insensitive is attributed to the intricate hydrogen bond network.5,6 In addition, this material has been found to be good performance on highsensitive force sensor.7 For energetic materials, the structure stability is one of the most important properties. At ambient conditions, LLM-105 behaves as a wavelike π-π stacking packing arrangement within a monoclinic structure (P21/n(14): a=5.642 Å, b = 15.956 Å, c =8.455 Å, β = 100.93°, V = 747.38 Å3 , Z=4) 10,11. Figure S1 shows the structure of LLM-105 crystal. The big π-bond and strong intramolecular hydrogen bonds allow LLM-105 molecules to exhibit a layered configuration and the intermolecular hydrogen bonding networks lead its high stability up to 513 K. 9 High pressure can shorten the distance between molecules and induce the different molecular conformers and/or phase transformation of crystal. In our previous investigation for hexahydro-1,3,5trinitro-1,3,5-triazine (RDX), more than six phases were generated by high pressure up to 50 GPa at room temperature.12 Few experimental reports about phase structure of LLM-105 under high pressure was provided except Stavrou et al’s work6, and no phase transition has been confirmed. In the other side many groups investigated the structure evolution of LLM-105 under high pressure in thoretical.4-6 Wu et al.4 predicted that a series of phase transitions exists at 8, 17, 25 and 42 GPa based on the periodic density functional theory (DFT) calculations. While, Manaa et al.5 employed dispersion-corrected DFT calculations to study the hydrostatic compression of crystal LLM-105 up to 45 GPa and suggested that there is no evidence for structural phase transition and the ambient phase remains stable up to 20 GPa. Zong et al.11 predicted a sudden change in the lattice parameters which may indicate a phase transition at about 30 GPa, but the new structure still remains uncertain. So these contradictory conclusions from different theoretical groups need to be clarified by experimental evidence under high pressure. Raman and Infrared spectra are the conventional methods to explore the evolutional processes of energetic materials under high pressure, Because the vibrational frequencies are sensitive to structural changes.11-16 The energetic materials with aromatic ring usually possess a lot of Raman or Infrared vibrational modes. And these modes are difficult to identify due to disturbance such as combination from other modes. But the stretching modes of methyl group, amino group and hydroxyl group always localize in the higher wavenumber regions due to the lighter oscillator containing H atom and they can be well identified. And the methyl group, amino group and hydroxyl group are closely related to


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structural changes. So these stretching vibrations can provide the evolutional information for energetic materials under high pressure and help us to further understand the pressure role. In this paper we employed X-ray diffraction, Raman and Infrared spectroscopy to confirm the structure stability of LLM-105 crystal under high pressure up to 34.7 GPa and under different temperature from 5 K to 363 K. The bond constants of NH2 group in LLM-105 crystal are obtained with different pressure and temperature. These constants can help us have a better understand of crystal stability and verify the correctness of the theoretical calculation. And the Grüuneisen Parameters for Raman modes are also obtained.

Experiments LLM-105 crystals sample from China Academy of Engineering Physics were used in our experiment without further purification. Under Cu Kα radiation (λ=1.542 Å), the XRD patterns at low temperature from 5 K to 280 K were measured by Rigaku Smartlab with a cool stage, for the high temperatures more than 280 K were measured by Rigaku Smartlab with a heat stage. As for the low temperature measurements, finely powdered sample was placed on a fluted copper sample holder, then the sample holder was placed on a copper block which was cooled by using a liquid helium cryostat. During the high temperature measurements, same powdered sample was placed on a platinum sample holder with a small heater in it. Temperature-dependent data were collected with the increasing temperature with steps of 20 K. At each temperature the sample was equilibrated for about 30 min before recording the data. The XRD pattern was analyzed by Rietveld method using MAUD software package.17,18 Raman spectra were recorded by using an integrated laser Raman system (LABRAM HR, Jobin Yvon) which equipped a confocal microscope, a spectrometer, and a multichannel air-cooled CCD detector. The 633 nm and 785 nm lasers were used as the excitation sources at a power level of about 7 mW. In situ temperature-dependent Raman spectra were recorded from 25 K to 513 K. A liquid helium cryostat was used to cool the sample from 25 K to 280 K. In the high temperature Raman measurement, a heating stage (TS1500) with a solid heater (TMS94/1500) were employed. Spectra were recorded in the backscattering geometry. In the high pressure experiment, the sample and ruby (as the pressure standard) were loaded into the sample chamber of diamond anvil cell (DAC, with 400 µm diameter culets) for in situ high pressure measurements. The stainless steel gasket was preindented to about 60 µm thickness and drilled by a spark eroder (BETSA, MH20M) to make a 130 µm diameter hole as the sample chamber. A 4:1 (v/v) mixture of methanol and ethanol was employed as the pressure-transmitting medium (PTM) in high pressure Raman measurement and KBr was used as PTM in infrared spectra measurement.19 The pressure was measured by the R1 fluorescence line of ruby.20 The high pressure Raman spectroscopy 3 ACS Paragon Plus Environment


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were measured by the same Raman system (LABRAM HR, Jobin Yvon) with a long focal length objective. The high pressure dependent Infrared spectroscopy were measured by TENSOR37 with a microscopy (HYPERION) at National Synchrotron Radiation Laboratory. All the high pressure experiment was occurred under room temperature. High pressure synchrotron X-ray diffraction experiment were performed at beamline 15U1 with X-ray beams (0.6199 Å, 20 keV) at Shanghai Synchrotron Radiation Facility (SSRF), China. And the beam was focused to a spot with size of 4∼6 µm. The XRD patterns were integrated with program FIT2D 2123.

Results & Discussion The X-ray diffraction patterns are shown in Fig. 1(a) for fine powdered crystal of LLM-105 under high pressure up to 42 GPa. With the increasing pressure up to 25 GPa, all diffraction peaks shift to higher angle, indicating the crystal unit cell contracts. At same time all peaks broaden out and gradually loss their intensities. Over 25 GPa, some peaks such as (1 2 0), (1 2 1) and (1 3 1) are indistinguishable for their too low intensities apart from several peaks as (0 1 1), (0 1 2), (1 4 1) and (1 5 1). At 30.6 GPa, three new peaks occur at 5.88°, 8.40°and 8.63° as marked by asterisks. This indicates a phase transition and this pressure value agrees with the predicted phase transition point in Zong’s work11 based on the first principle calculation. And these peaks still exist at higher pressure, though the intensity is lower. As for the structure information of the observed new phase, it is difficult to observe from the current XRD patterns due to the broadening peaks and bad signal/noise ratio, some complex calculating works are necessary in future. The obtained XRD patterns for this new phase provide the criteria of the computing structure. The lattice constants under high pressure up to 25 GPa are given in Fig. 1(b). The results below 20 GPa are similar to the work from Ref. 6. Pressure-dependent lattice constants reveal that the b-axis is more compressible below 7 GPa. The reason is that the stacking of plane molecule of LLM-105 along b-axis induces the larger compressional space as seen in Fig.S1. The unit cell volume under high pressure is fitted with the third-order Birch-Murnaghan equation of state (EOS)24. The fitting result was shown in Fig. 1(c). 𝐵0 and 𝐵′0 are 19.23 GPa and 6.700, respectively. The volume of LLM105 at 25 GPa has decreased 35% comparing with ambient condition. This result and recently work of bulk modulus are summarized in Table 1. It can be seen that our result is agree well with reported experiments6,9 and published calculations5,11. LLM-105 crystal possesses rich Raman vibration modes with 76 atoms of four molecules in a unit cell.10,11 The mechanical representation of this symmetry is described by Eq. (1). M = 57Ag+57Au +57Bg+57Bu Which includes 3 acoustic modes in Eq. (2) and 255 optical modes in Eq. (3). 4 ACS Paragon Plus Environment

(1)

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Γoptic = Au+2Bu

(2)

Γ = 57Ag +56Au +57Bg+55Bu

(3)

Group-theoretical analysis reveals that the 57Ag+57Bg modes are Raman-active and 56Au+55Bu modes are infrared-active. Figure 2 shows Raman and Infrared spectra with the distinguishable peaks of vibration modes at ambient condition for LLM-105 crystal. The observed peaks number is much lower than the predicating 114 and 111 for Raman and IR modes, respectively, which indicates that there exists the high degeneration for some vibrational modes. The vibrations at 57, 72, 85, 91, and 106 cm1

are attributed to external modes. And the eleven peaks from 151 cm-1 to 480 cm-1 are response to the

mixture of external and internal modes. The frequencies from 480 cm-1 to 557 cm-1 are the wagging vibrational modes of NH2 groups, and 700, 713, 734 and 757 cm-1 are twisting vibrational modes of ring and NH2 groups, which is similar to another energetic material Fox-7.25,26, The vibrations from 814 cm-1 to 1680 cm-1 are related to the ring, NH2 groups and NO2 groups. The higher frequencies from 3100 cm-1 to 3600 cm-1 are attributed to the stretching vibrational modes of NH2 groups. The abundant vibrational modes of NH2 groups revealed the different NH2 groups with different circumstance in LLM-105 crystal which will be discussed below. The Infrared spectrum is similar to Raman spectrum as shown in Fig. 2, but some difference on the intensity. To understand the stability of LLM-105 crystal under high pressure, the Raman and Infrared spectra at different pressures were measured and shown in Fig. 3. Figure 3(a) presents the Raman spectra from 50 to 1680 cm-1 under high pressure up to 31.5 GPa. The strong peak at 1330 cm-1 is from diamond of DAC setup. All peaks gradually broaden and lost their intensities with increasing pressure. The broadening mainly results from the larger pressure gradient and the weaker peaks are due to lattice distortion. For the stretching vibrational modes of NH2 group at high frequency region, these Raman peaks also lost their intensities, broaden gradually and are finally undetectable at 9.7 GPa as seen in Fig. 3(b), but these vibrational modes do not disappear which can be confirmed in the pressure dependent infrared spectra up to 34.7 GPa as shown in Fig. 3(c). Figure 4 provided some regional magnifying and the relative Raman peak shifts under high pressure. The lattice modes in Figs. 4(a) and (b) display rapid blue shift below 5 GPa due to the b-axis is more compressible as description above mentioned. The modes about deformations of ring and amino groups show the slow shift in the lower pressure region as seen Figs. 4(c-d). This indicates that the vibrations from intramolecular are hardly influenced under lower pressure. With continuing compression up to 25 GPa, all modes rapidly shift to blue. The trending is modified over 25 GPa. At 31.5 GPa, Raman peaks at 151 cm-1 (lattice mode), 320 cm-1 (mixture of lattice mode and NO2 rock) and 657 cm-1 (NH2 wag, ring twist) disappear, the vibrations at 140 cm-1 and 229 cm-1(lattice mode), 468 cm-1 (NH2 & N-O in ring rocking) and 802 cm-1 (NH2 twisting, ring twisting) show an faster shift toward higher frequency 5 ACS Paragon Plus Environment


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and the Raman mode at 560 cm-1 (NH2 wagging) shows a slower shift toward higher frequency. The difference of lattice modes under different pressures reveals a structural change in LLM-105 crystal. These unusual behavior of Raman modes indicates a phase transition begins at 25.6 GPa and finishes at about 31.5 GPa, which is agree with our high pressure XRD result as mentioned above. Figure S2 shows the pressure induced shifts of these modes. The lattice vibration modes in the low frequency region present normal blue shifts with increasing pressure, which has been observed in many other organic crystals26-29. The blue shift of lattice vibration modes is considered to be the result of the smaller intermolecular distance and the stronger intermolecular interactions under compressed. With the increasing pressure, the force constant enhances due to the pressure-induced smaller intermolecular distance. In addition, the shift rates of the lattice vibration modes decrease gradually with increasing pressure, which can be ascribed to the reduction of volumetric compression which has already been observed in experiment and computation. 6 In LLM-105 crystal, the hydrogen bonding networks play an important role in structural stability. The intramolecular hydrogen bonds consist of N-H…O2-N or N-H…O-N-C2, the intermolecular hydrogen bonds are connected through amine groups with nitro groups from adjacent molecules. The strength of the hydrogen bond is related to the N-H bond. To study the evolution of hydrogen bond under pressure, pressure dependent Raman and Infrared spectra of the ν(NH2) stretching modes were measured as shown in Figs. 3 (b) and (c), the frequency shift behavior under pressure of these modes were shown in Fig. 5(a). Combined the Raman and Infrared spectra, there are seven modes can be resolved for amino group stretching vibrations, this means that there are four different kinds of amino groups. It’s easy to understand that each unit cell of LLM-105 possesses 8 amino groups. The different stretching vibrational frequencies reveal the different bond angle and bond length for amino groups each other. On the other hand, 8 amino groups should generate 16 stretching modes including 8 asymmetric modes and 8 symmetric modes. The observed 7 modes (as shown in Fig. S3) confirm the higher degenerating characteristics for amino groups of LLM-105. The bond-stretching force constant and bond angle of NH2 can be descripted by the following Eqs. (4) and (5).30 1

𝜈𝑠 = 2𝜋𝑐 [𝜇1 + 𝜇2(1 + 𝑐𝑜𝑠𝜑)](𝑓𝑟 + 𝑓𝑟𝑟) ― 2𝜇2𝑓𝑟𝜑

(4)

1

𝜈𝑎𝑠 = 2𝜋𝑐 [𝜇1 + 𝜇2(1 ― 𝑐𝑜𝑠𝜑)](𝑓𝑟 ― 𝑓𝑟𝑟)

(5)

Where 𝜈𝑠 and 𝜈𝑎𝑠 are the frequencies for symmetric and asymmetric stretching vibrations, respectively. 1

1

µ is the reciprocal of effective mass for oscillator, as for amino group 𝜇1 = 𝑚𝐻, 𝜇2 = 𝑚𝑁. 𝜑 is the bond angle of NH2, 𝑓𝑟, 𝑓𝑟𝑟 and 𝑓𝑟𝜑 correspond to bond stretching force constant, bond-bond interaction force constant and bond-angle force constant of NH2, respectively. The observed frequencies of stretching vibration modes for amino groups exist a difference value in the range of 80 cm-1 to 130 cm-1 between 6 ACS Paragon Plus Environment

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𝜈𝑎𝑠 and 𝜈𝑠 . The large difference means that the bond-bond interaction and bond-angle interaction are very weak and ignorable. Considering that 𝜑 is around 120°, and 𝑓𝑟 about 6 dyn/cm. Based on the infrared spectra, we propose that 3432 cm-1, 3402 cm-1, 3283 cm-1 and 3228 cm-1 respond to the asymmetric stretching modes, 3301 cm-1, 3283 cm-1, 3192 cm-1 and 3150cm-1 belong to the symmetric stretching modes. 3283 cm-1 peak with larger intensity and width is recognized as a mix mode from one asymmetric stretching mode and another symmetric stretching mode. Based on the Eqs. (4) and (5), 8 vibration modes are precisely assigned to 4 pairs asymmetric and symmetric stretching modes [𝜈𝑎𝑠,𝜈𝑠 ] as [3432, 3301], [3402, 3283], [3283, 3192] and [3228, 3150]. Asymmetric and symmetric modes from same group are correlative each other and can be determined from Eq. (4) and Eq. (5). As soon as one couple is confirmed, the evolution of modes is facilely traced with variable temperature and /or pressure. With the increasing pressure, the modes at 3402 cm-1 and 3283cm-1 show a red shift while others are normally blue shift. This softening mode probably comes from the amino which has a stronger hydrogen-bonding effect under higher pressure. Based on our synchrotron high pressure XRD patterns and an earlier literature6, the b-axis compressibility is significantly larger than a- and c-axis, which means that the intermolecular hydrogen-bonding effect becomes stronger with the increasing pressure. The pressure dependent bond-stretching force constant and bond angle of NH2 groups were shown in Figs. 5 (b) and (c). Uploading pressure, the bond-stretching force constant of the softening amino group with [3402, 3283] presents a slightly decreasing trend, and the bond angle increases to 123.39° at 5.6 GPa then decreases. The mode softening is attributed to pressure inducing the rotation of amino groups around N-N bond as description in our other work about TATB31. For other normally blue shift modes, the force constants all show an increasing trend with a decreasing bond angle. Grüneisen parameter (γ)32-36, which is always used to evaluate how volume changes affect the vibrational properties. The isothermal bulk modulus of LLM-105 is taken as 19 GPa. The obtained γ values are listed in table 2. The Grüneisen parameters of external modes are significant larger than those of internal modes. As for internal modes, the very small Grüneisen parameters reveal the volume change has little effect on internal modes due to a big void space in LLM-105 crystal. The phase and structure of LLM-105 at different temperature were analyzed with Rietveld method by using the structure reported in the earlier work.37-38 The background of XRD data was fitted by a fourthorder polynomial, and peaks were modeled by a convolution equation according to Enzo et al35. All temperature-dependent XRD patterns can be well refined with the room temperature structural data. The results of refined XRD patterns at 5 K and 363 K are shown in Fig. 6. The result indicates no phase transition occurrence from 5 K to 363 K. LLM-105 crystal shows anisotropic response to the pressure as mentioned above. Temperature evolution of unit cell parameters for LLM-105 crystal was shown in Fig.7. With lowering temperature, the lattice parameters show a descending trend. And just like the case 7 ACS Paragon Plus Environment


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under high pressure, the b-axis shows a significantly larger contraction trend with decreasing temperature than that of a- and c- axis. Comparing Fig. 7 with Fig. 1 the contracting effect from room temperature to 5 K is similar to that of compression up to about 0.68 GPa. The typical axial thermal expansion coefficients of LLM-105 obtained from the unit cell parameters between 160 K and 360 K are αa = 3.44×10-5 K-1, αb = 8.47×10-5 K-1 and αc = 3.44×10-5 K-1, and the volume thermal expansion (αV) is 1.49×10-4 K-1 as shown in table 3. The expansion advantage along baxis indicates an anisotropic thermal expansion of the lattice. The similar anisotropic behavior has also been observed for LLM-105 crystal under high pressure. The axial compression factors are

βb =

9.85×10-3 GPa-1, βa = 6.51×10-3 GPa-1 and βc = 5.68×10-3 GPa-1 within the region from 0.3 GPa to 11.6 GPa. Furthermore, it can be noticed that, below 160 K, the cooling contraction coefficients are αa = 1.33×10-5 K-1, αb = 5.95×10-5 K-1, αc = 1.89×10-5 K-1, which are smaller than the value in the region of higher temperature. The difference in thermal expansion behavior at lower temperature (βa > βc. With Rietveld method, we refined the temperature dependent XRD result of LLM-105 crystal and obtained its anisotropic thermal expansion in the order αb > αc ≈ αa. Debye temperature of 1125K is obtained based on the measured expansion coefficient and compressibility for LLM-105 crystal. Combining Debye heat capacity curve and P-V curve, compression is a better path to contract the volume of LLM-105 crystal comparing with cooling. Based on the Raman and Infrared spectroscopy, we assigned the vibrational modes of amino groups and obtained the bond constants at different pressure and temperature. And the temperature dependent Raman spectrum also presents anharmonicity effect exist in LLM-105 crystal.

Supporting Information The structure of LLM-105 crystal, Raman shifts of LLM-105 crystal, vibrational modes of amino groups, diagram of amino group's vibration

Acknowledgements This work was supported by the National Natural Science Foundation of China (Grant Nos. 11672273), the Science Challenge Project (No. TZ2016001), beam line 15 U1 of the Shanghai Synchrotron 10 ACS Paragon Plus Environment

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Radiation Facility (SSRF), infrared spectroscopy and micro spectroscopy at National Synchrotron Radiation Laboratory (NSRL, Hefei) and Supercomputing Center of University of Science and Technology of China. Author contributions: Z. Zhang, Z. Xu, H. Li, R. Dai, Z. Wang and X. Zhou design the experiment. X. Zhou and H. Li synthesized the high quality crystal samples. Z. Xu and H. Su performed the experiment. Z. Xu, X. Wang and J. Wang do the calculations. Z. Xu, H. Su, X. Zhou, X. Wang, J. Wang, C. Gao, X. Sun, R. Dai, Z. Wang, H. Li and Z. Zhang take part in discussion. Z. Xu and Z. Zhang write and revise the manuscript.

Conflict of interest All the authors declare that they have no conflict of interest and they are responsible for content and writing of paper.

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[20] Mao, H. K.; Bell, P. M.; Shaner, J. W.; Steinberg, D. J. Specific volume measurements of Cu, Mo, Pd, and Ag and calibration of the ruby R1 fluorescence pressure gauge from 0.06 to 1 Mbar. J. Appl. Phys. 1978, 49, 3276-3283. [21] Hammersley, A. P.; Riekel, C. MFIT: Multiple spectra fitting program. Synch. Rad. News . 1989, 2, 24-26. [22] Zhao, Y.; Zhang, J.; Han, B.; Song, J.; Li, J.; Wang, Q. Metal-organic framework nanospheres with well-ordered mesopores synthesized in an ionic liquid/CO2/surfactant system. Angew. Chem. Int. Edit. 2011, 50, 636-639. [23] Hammersley, A. P. FIT2D: a multi-purpose data reduction, analysis and visualization program. J. Appl. Crystallogr. 2016, 49, 646-652. [24] Birch, F. Finite elastic strain of cubic crystals. Physical review. Phys. Rev. 1947, 71, 809. [25] Dreger, Z. A.; Tao, Y.; Averkiev, B. B.; Gupta, Y. M.; Klapötke, T. M. High-pressure stability of energetic crystal of dihydroxylammonium 5, 5’-bistetrazole-1, 1’-diolate: Raman spectroscopy and DFT calculations. J. Phys. Chem. B. 2015, 119, 6836-6847. [26] Dreger, Z. A.; Tao, Y.; Gupta, Y. M. High-pressure vibrational and polymorphic response of 1, 1-diamino-2, 2-dinitroethene single crystals: Raman spectroscopy. J. Phys. Chem. A. 2014, 118, 5002-5012. [27] Ciezak, J. A.; Jenkins, T. A.; Liu, Z.; Hemley, R. J. High-pressure vibrational spectroscopy of energetic materials: Hexahydro-1, 3, 5-trinitro-1, 3, 5-triazine. J. Phys. Chem. A. 2007, 111, 59-63. [28] Klapötke, T. M.; Witkowski, T. G.; Wilk, Z.; Hadzik, J. Determination of the initiating capability of detonators containing TKX-50, MAD-X1, PETNC, DAAF, RDX, HMX or PETN as a base charge, by underwater explosion test. Propellants, Explos., Pyrotech. . 2016, 41, 92-97. [29] Chellappa, R. S.; Dattelbaum, D. M.; Coe, J. D.; Velisavljevic, N.; Stevens, L. L.; Liu, Z. Intermolecular Stabilization of 3, 3’-Diamino-4, 4’-azoxyfurazan (DAAF) Compressed to 20 GPa. J. Phys. Chem. A. 2014, 118, 5969-5982. [30] Coates, J. Interpretation of Infrared Spectra, A Practical Approach; John Wiley & Sons, Chichester, U.K., 2000; pp 10815– 10837. [31] Ojeda, O. U.; Çağın, T. Hydrogen bonding and molecular rearrangement in 1, 3, 5-triamino2, 4, 6-trinitrobenzene under compression. J. Phys. Chem. B. 2011, 115, 12085-12093. [32] Peiris, S. M.; Wong, C. P.; Zerilli, F. J. Equation of state and structural changes in diaminodinitroethylene under compression. J. Chem. Phys. 2004, 120, 8060-8066. 13 ACS Paragon Plus Environment


[33] Sawyer, J. O.; Hyde, B. G.; Eyring, L. R. Pressure and polymorphism in the rare earth sesquioxides. Inorg. Chem. 1965, 4, 426-427. [34] Dohcevic-Mitrovic, Z.; Popovic, Z. V. Anharmonicity effects in nanocrystals studied by Raman scattering spectroscopy. Acta Phys. Pol., A. 2009, 116, 36. [35] Pandey, S. D.; Samanta, K.; Singh, J.; Sharma, N. D.; Bandyopadhyay, A. K. Raman scattering of rare earth sesquioxide Ho2O3: A pressure and temperature dependent study. J. Appl. Phys. 2014, 116, 133504. [36] Pandey, S. D.; Samanta, K.; Singh, J.; Sharma, N. D.; Bandyopadhyay, A. K. Anharmonic behavior and structural phase transition in Yb2O3. AIP Adv. 2013, 3, 122123. [37] Lutterotti, L.; Scardi, P. Simultaneous structure and size-strain refinement by the Rietveld method. J. Appl. Crystallogr. 1990, 23, 246-252. [38] Gilardi, R. D.; Butcher, R. J. 2,6-Diamino-3,5-dinitro-1,4-pyrazine dimethyl sulfoxide solvate. Acta Crystallogr., Sect. E: Struct. Rep. Online. 2001, 57, o757-o759. [39] Ma, H.; Song, J.; Zhao, F.; Gao, H.; Hu, R. Crystal Structure, Safety Performance and DensityFunctional Theoretical Investigation of 2,6-Diamino-3,5-dinitropyrazine-1-oxide (LLM-105). Chin. J. Chem.. 2008, 26, 1997-2002.


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Table Captions: Table 1: Bulk modulus and it's derivative of LLM-105 crystal Table 2: The frequencies, pressure coefficients, and Grüuneisen Parameter (γi) for Raman vibrational modes in LLM-105 Table 3: The typical axial thermal expansion coefficients of LLM-105 between 160 K and 360 K and the axial compressibility Table 4: The energy cost of reducing the volume of LLM-105 crystal by compression and cooling. Table 1 works

𝐵0(GPa)

𝐵′0

This work

19.23

6.70

Exp. (6)

15

9

Exp. (9)

11.19

18.54

Cal. (5)

17.4

7.9

Cal. (21)

16.5

9.4

Table 2 Mode frequency(cm-1)

dω/dP(cm-1/GPa)

γi

57

2.25

0.59

72

2.31

0.48

85

2.22

0.37

91

3.76

0.62

106

3.38

0.48

133

6.00

0.68

151

6.91

0.69

175

6.00

0.52

181

8.22

0.68

218

6.22

0.43

229

7.34

0.48

3.8 GPa



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Table 3 Axial

a

b

c

Thermal expansion coefficients（10-5 K-1）

3.44

8.47

3.44

Compressibility（×10-3 GPa-1）

6.51

9.85

5.68

Table 4 Unit cell Volume (Å3)

Energy (eV)

Energy by DFT (eV)

P (GPa)

1 atm

756.6

at 300 K

0.68

732.0

T (K)

300

756.6

5

732.0

0.052 (by P-V curve)

at ambient

1.018 (by Cv-T curve)

pressure


0.061

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Figure Captions: Figure 1: The structure parameters of LLM-105 crystal under high pressure, (a) The synchrotron X-ray diffraction patterns , (b) the lattice constants, and (c) the unit cell volume. Figure 2: Typical Raman and Infrared spectrum of LLM-105 crystal at ambient. Figure 3: Raman spectra of LLM-105 crystal under high pressure in the range of (a) 50-1680 cm-1, (b) 3000-3600 cm-1. (c) Infrared spectra of LLM-105 crystal under high pressure. Figure 4: Pressure induced shifts of Raman modes of LLM-105 crystal, (a-b) lattice modes, (c-d) deformations of ring and amino groups. Figure 5: Pressure dependent IR modes and bond paprameters in LLM-105 crystal : (a) shifts of Infrared modes from amino, (b) the bond constant of N-H in amino groups, and (c) bond angle of H-N-H in amino groups. Figure 6: The result of refined XRD patterns of LLM-105 crystal at 5 K and 363 K. Figure 7: Temperature evolution of unit cell parameters of LLM-105 crystal. The solid points is the unit cell parameters under low temperature measured by the machine with a cooling system and the hollow points is the high temperature XRD data measured by another machine with a heating system. Figure 8: Temperature dependent Raman spectra of LLM-105 crystal, low temperature from 25 K to 280 K in the range of (a) 50-1680 cm-1, and (b) 3100-3600 cm-1, and (c) high temperature from 293 K to 513 K. Figure 9: Temperature-dependent Raman shifts and bond parameters, (a)frequencies shifts for ν(NH2) stretching modes. (b) the bond constant of N-H in amino groups, and(c) bond angle of H-N-H in amino groups. (d) The Raman shift for ν(NH2) stretching modes as pressure increasing (solid points) and temperature decreasing (hollow points).



Figure 1


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Figure 2



Figure 3


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Figure 4



Figure 5


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Figure 6



Figure 7


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Figure 8



Figure 9


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TOC Graphic:



Figure 1: The structure parameters of LLM-105 crystal under high pressure, (a) The synchrotron X-ray diffraction patterns , (b) the lattice constants, and (c) the unit cell volume. 99x53mm (300 x 300 DPI)

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Figure 2: Typical Raman and Infrared spectrum of LLM-105 crystal at ambient. 99x66mm (300 x 300 DPI)



Figure 3: Raman spectra of LLM-105 crystal under high pressure in the range of (a) 50-1680 cm-1, (b) 3000-3600 cm-1. (c)Infrared spectra of LLM-105 crystal under high pressure. 42x42mm (300 x 300 DPI)


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Figure 4: Pressure induced shifts of Raman modes of LLM-105 crystal, (a-b) lattice modes, (c-d) deformations of ring and amino groups. 99x44mm (300 x 300 DPI)



Pressure dependent IR modes and bond paprameters in LLM-105 crystal : (a) shifts of Infrared modes from amino, (b) the bond constant of N-H in amino groups, and (c) bond angle of H-N-H in amino groups. 99x49mm (300 x 300 DPI)


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Figure 6: The result of refined XRD patterns of LLM-105 crystal at 5 K and 363 K. 79x95mm (300 x 300 DPI)



Temperature evolution of unit cell parameters of LLM-105 crystal. The solid points is the unit cell parameters under low temperature measured by the machine with a cooling system and the hollow points is the high temperature XRD data measured by another machine with a heating system. 99x80mm (300 x 300 DPI)


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Figure 8: Temperature dependent Raman spectra of LLM-105 crystal, low temperature from 25 K to 280 K in the range of (a) 50-1680 cm-1, and (b) 3100-3600 cm-1, and (c) high temperature from 293 K to 513 K. 80x80mm (300 x 300 DPI)



Figure 9: Temperature-dependent Raman shifts and bond parameters, (a)frequencies shifts for ν(NH2) stretching modes. (b) the bond constant of N-H in amino groups, and(c) bond angle of H-N-H in amino groups. 99x44mm (300 x 300 DPI)


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Pressure- and Temperature-Dependent Structural Stability of LLM-105

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