Raman spectroscopy investigation on the pressure-induced structural and magnetic phase transition in two-dimensional antiferromagnet FePS_(3)

The layered van der Waals antiferromagnetic Fe PS_(3) has received considerable attention because long range magnetic ordering can remain with single atoms layer,which offers potential applications in future ultrathin devices.Here,we perform Raman spectroscopy to systematically explore the variations of lattice vibration and crystal structure under pressure up to 18.9 GPa.We observe two structural phase transitions at approximately 4 GPa and 13 GPa,respectively.Moreover,by monitoring spin-related Raman modes,we demonstrate a pressure-induced magnetic structure transition above 2 GPa.These modes disappear accompanying the second structural phase transition and insulator-to-metal transition(IMT),indicating the suppression of long-range magnetic ordering,in agreement with earlier neutron powder diffraction experiments.

High-pressure Raman study of MgV_2O_6synthesized at highpressure and high temperature

A new structural phase of MgV2O6 was obtained by a high-pressure, high-temperature （HPHT） synthesis method. The new phase was investigated by the Rietveld analysis of X-ray powder diffraction data, showing space group Pbcn （No. 60） symmetry and a = 13.6113（6）A （1A =0.1 nm）, b = 5.5809（1）A, c = 4.8566（3）A, V = 368.93（2）A3 （Z = 4）. High pressure behavior was studied by Raman spectroscopy at room temperature. Under 22.5 GPa, there was no sign of a structural phase transition in the spectra, demonstrating stability of the HPHT phase up to the highest pressure.

High-Pressure Raman Study on Anglesite

High-pressure Raman spectroscopic experiments of anglesite, PbSO4, were carried out in a diamond anvil cell up to about 35 GPa at room temperature. Two stages of changes in the pattern of wavenumber-versus-pressure plot were observed in most of the vibrational modes. The first stage of change is the kink in the slope of wavenumber-versus-pressure plot at about 14 GPa, indicating a change in the force constant of modes. Further compression up to 21 GPa causes the splitting in the S-O stretching modes, representing the distortion of SO4 tetrahedron. The behavior of transition observed in PbSO4 is similar to that of BaSO4 as well as those found in the solid solution series of BaSO4-SrSO4. Transitions taking place at higher pressure for anglesite is due to the relatively greater value of electronegativity for Pb2+, as compared with M2+ in other complex compounds of similar structure.

Methane formation from CaCO_3 reduction catalyzed by high pressure

Under high pressures of several giga-pascals using hydrothermal diamond anvil cell,methane generated directly from CaCO3 reduction in gold-lined chamber is in situ measured by Raman spectroscopy at the temperature of 550℃ Fhe reducing agents include FeO,SiO and natural fayalite（Fe2SiO4）,and the resource of hydrogen are water and natural serpentine（Mg3Si2O5（OH）4）. The study demonstrates the existence of abiogenic formation of methane under high pressures in the Earth＇s interior and that the application of high pressure to catalyze multicomponent reactions is a very promising method.

High-pressure investigations on the isostructural phase transition and metallization in realgar with diamond anvil cells

The high-pressure structural,vibrational and electrical properties for realgar were investigated by in-situ Raman scattering and electrical conductivity experiments combined with first-principle calculations up to~30.8 GPa.It was verified that realgar underwent an isostructural phase transition at~6.3 GPa and a metallization at a higher pressure of~23.5 GPa.The isostructural phase transition was well evidenced by the obvious variations of Raman peaks,electrical conductivity,crystal parameters and the As–S bond length.The phase transition of metallization was in closely associated with the closure of bandgap rather than caused by the structural phase transition.And furthermore,the metallic realgar exhibited a relatively low compressibility with the unit cell volume V_(0)=718.1.4Å^(3)and bulk modulus B_(0)=36.1 GPa.

Photothermal-chemical synthesis of P-S-H ternary hydride at high pressures

The recent discovery of room temperature superconductivity(283 K)in carbonaceous sulfur hydride(C-S-H)has attracted much interest in ternary hydrogen rich materials.In this report,ternary hydride P-S-H was synthesized through a photothermal-chemical reaction from elemental sulfur(S),phosphorus(P)and molecular hydrogen(H_(2))at high pressures and room temperature.Raman spectroscopy under pressure shows that H_(2)S and PH_(3) compounds are synthesized after laser heating at 0.9 GPa,and a ternary van der Waals compound P-S-H is synthesized with further compression to 4.6 GPa.The P-S-H compound is probably a mixed alloy of PH_(3) and(H_(2)S)_(2)H_(2) with a guest-host structure similar to the C-S-H system.The ternary hydride can persist up to 35.6 GPa at least and shows two phase transitions at approximately 23.6 GPa and 32.8 GPa,respectively.

Synthesis of ternary compound in H-S-Se system at high pressures

The chemical reaction products of elemental sulfur(S),selenium(Se),and molecular hydrogen(H_(2))at high pressures and room temperature are probed by Raman spectroscopy.Two known compounds H_(2)S and H_(2)Se can be synthesized after laser heating at pressures lower than 1 GPa.Under further compression at room temperature,an H_(2)S-H_(2)Se and an H_(2)S-H_(2)Se-H_(2)van der Waals compounds are synthesized at 4 GPa and 6 GPa,respectively.The later is of guest-host structure and can be identified as(H_(2)S)x(H_(2)Se)(2-x)H_(2).It can be maintained up to 37 GPa at least,and the stability of its H_(2)Se molecules is extended:the H-Se stretching mode can be detected at least to 36 GPa but disappears at 22 GPa in(H_(2)Se)2H_(2).The pressure dependence of S-H and Se-H stretching modes of this ternary compound is in line with that of(H_(2)S)2 H_(2)and(H_(2)Se)2H_(2),respectively.However,its hydrogen subsystem only shows the relevance to(H_(2)S)2H_(2),indicating that this ternary compound can be viewed as H_(2)Se-replaced partial H_(2)S of(H_(2)S)2H_(2).

Structural evolution and bandgap modulation of layeredβ-GeSe_(2)single crystal under high pressure

Germanium diselenide(GeSe_(2))is a promising candidate for electronic devices because of its unique crystal structure and optoelectronic properties.However,the evolution of lattice and electronic structure ofβ-GeSe_(2)at high pressure is still uncertain.Here we prepared high-qualityβ-GeSe_(2)single crystals by chemical vapor transfer(CVT)technique and performed systematic experimental studies on the evolution of lattice structure and bandgap ofβ-GeSe_(2)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 ofβ-GeSe_(2)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 ofβ-GeSe_(2)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 ofβ-GeSe_(2)and demonstrate the potential of pressure in modulating the material properties of two-dimensional(2D)Ge-based binary material.

High-Pressure Behavior of Ferromagnesite(Mg_(0.81)Fe_(0.19))CO_(3)by Synchrotron X-Ray Diffraction and Raman Spectroscopy up to 53 GPa

Ferromagnesite(Mg,Fe)CO_(3)with 20 mol%iron is a potential host mineral for carbon transport and storage in the Earth mantle.The high-pressure behavior of synthetic ferromagnesite(Mg_(0.81)Fe_(0.19))CO_(3)up to 53 GPa was investigated by synchrotron X-ray diffraction(XRD)and Raman spectroscopy.The iron bearing carbonate underwent spin transition at around 44–46 GPa accompanied by a volume collapse of 1.8%,which also demonstrated a variation in the dνi/dP slope of the Raman modes.The pressure-volume data was fitted by a third-order Birch-Murnaghan equation of state(BM-EoS)for the high spin phase.The best-fit K_(0)=108(1)GPa and K_(0)'=4.2(1).Combining the dνi/dP and the K_(0),the mode Grüneisen parameters of each vibrational mode(T,L,ν4 andν1)were calculated.The effects of iron concentration on the Mg_(1−x)Fe_(x)CO_(3)system related to high-pressure compressibility and vibrational properties are discussed.These results expand the knowledge of the physical properties of carbonates and provide insights to the potential deep carbon host.

微区Raman光谱在TiO_2高压结构相变研究中的应用

本文以金红石单晶TiO2和锐钛矿多晶TiO2为研究对象,应用金刚石小压机和原位拉曼光谱测量技术,系统研究了室温高压下TiO2的结构相变。原位拉曼测量表明,金红石单晶TiO2在压力达到12.91GPa时开始发生由金红石结构向斜锆石结构(MI)的相变,当压力达到14.16 GPa时,相变完成;继续加压到21.65 GPa,没有发现进一步的相变;卸压时由斜锆石结构转变为PbO2结构,相变发生在大约7.11 GPa处。锐钛矿多晶TiO2在压力达到4.26 GPa时开始向PbO2结构转变,当压力达到8.34 GPa时相变完成;继续加压到12.94 GPa,样品开始发生由PbO2结构向斜锆石结构的相变,当压力达到18.74 GPa时相变完成;继续加压到21.39 GPa,没有发现进一步的相变;卸压时也由斜锆石结构转变为PbO2结构,起始相变压力点应高于8 GPa。

高温高压下利用金刚石压腔实验技术对材料Raman光谱的研究

金刚石对顶砧装置(diamond anvil cell,DAC)是静态超高压装置的一种,由于金刚石具有高的硬度和良好的透光性,因此这种装置所实现的压力和能测量物性的种类都优于其他高压装置。Raman光谱是表征物质结构及其变化的一种重要手段,DAC超高压实验技术与激光Raman光谱测试方法相结合,为高压下物质结构相变研究提供了一种有效途径。实验利用金刚石压腔实验技术在高温高压条件下对氧化镓、硫酸锶固体材料进行了Raman光谱的测量。

Experimental and ab initio study of Ba_(2)Na_(3)(B_(3)O_(6))_(2)F stability in the pressure range of 0–10 GPa

Both numerical and experimental studies of the stability and electronic properties of barium–sodium metaborate Ba_(2)Na_(3)(B_(3)O_(6))_(2)F(P63/m) at pressures up to 10 GPa have been carried out. Electronic-structure calculations with HSE06 hybrid functional showed that Ba_(2)Na_(3)(B_(3)O_(6))_(2)F has an indirect band gap of 6.289 eV. A numerical study revealed the decomposition of Ba_(2)Na_(3)(B_(3)O_(6))_(2)F into the BaB_(2)O_(4),Na BO_(2), and NaF phases above 3.4 GPa at 300 K. Subsequent high-pressure high-temperature experiments performed using ‘Discoverer-1500’DIA-type apparatus at pressures of 3 and 6 GPa and temperature of 1173 K confirmed the stability of Ba_(2)Na_(3)(B_(3)O_(6))_(2)F at 3 GPa and its decomposition into BaB_(2)O_(4), NaBO_(2), and NaF at 6 GPa, which was verified by energy-dispersive X-ray analysis and Raman spectroscopy. The observed Raman bands of the Ba_(2)Na_(3)(B_(3)O_(6))_(2)F phase were assigned by comparing the experimental and calculated spectra. The experimental Raman spectra of decomposition reaction products obtained at 6 GPa suggest the origin of a new high-pressure modification of barium metaborate BaB_(2)O_(4).

高压拉曼光谱研究均苯四甲酸二酐

测量了常温常压下的均苯四甲酸二酐的拉曼光谱,并对所测量的各个拉曼谱线进行归属认证。获得了从常压到24GPa压强条件下的原位拉曼光谱,通过频率-压强关系曲线可以得出该材料在2Gpa存在晶体结构相变,定义了均苯四甲酸二酐在低于2GPa压强条件的晶体结构为相Ⅰ,高于2GPa压强条件的晶体结构相为相Ⅱ。在相变前后,绝大多数的拉曼谱线频率-压强曲线斜率变小,说明与相Ⅰ相比,各官能团对压强的敏感程度下降,相Ⅱ的分子晶体具有更紧密的堆积结构。拉曼光谱强度能够给出丰富的材料结构信息,通过对C—O伸缩振动的倍频(常压位于1837cm^(-1))和C=O伸缩振动基频(常压位于1865cm^(-1))的相对拉曼光谱强度随压强的变化规律进行分析,发现两拉曼谱线强度比在2GPa附近存在突变,为均苯四甲酸二酐在2GPa附近发生结构相变提供了实验依据。

高压下多硅白云母的拉曼光谱学研究

在金刚石压腔中,通过原位拉曼光谱研究了多硅白云母在常温高压下的稳定性。实验获得了多硅白云母从常压到20GPa的拉曼光谱数据,研究了多硅白云母的266、708和3618cm-1谱峰与压力的相关性。研究发现,多硅白云母的708cm-1谱峰随压力增加有规律地向高频方向偏移,与压力的增加呈明显的正相关性,即y(拉曼位移,cm-1)=0.5238x(压力,GPa)+712.31,相关系数R2=0.9656,并且该谱峰在压力4.7GPa时消失,这可能与多硅白云母中的Si、Al替代有关。羟基3618cm-1谱峰则随压力增加向低频方向移动,谱峰的降低与压力的增加呈明显的线性关系变化(y=-0.3402x+3617.8,R2=0.9662),并且强度随着压力的增加也在逐渐减弱,在压力达18GPa时开始消失,推测该压力可能为多硅白云母在常温下脱羟基的极限压力。

显微激光拉曼光谱原位观测甲烷水合物生成与分解的微观过程

采用显微激光拉曼光谱技术对高压透明毛细管中甲烷水合物的生成与分解的微观过程进行了原位观测,初步探讨了甲烷水合物笼型结构的变化规律。结果表明,甲烷水合物在生成过程中,甲烷分子的拉曼峰(2 917 cm-1)逐渐分裂为两个峰(2 905和2 915 cm-1),表明溶解态甲烷分子从单一的化学环境进入了两个有差异的化学环境中,这两个峰分别代表着水合物的大笼和小笼。同时,水的氢键作用由其液态向固态的转化而得到加强,使O—H键伸缩振动向低波数迁移。在甲烷水合物的分解过程中,大小笼中甲烷分子的拉曼双峰逐渐消解,并最终转化成单一的甲烷气体峰。显微激光拉曼光谱可以准确捕捉水合物生成与分解过程中其笼型结构变化的相关信息。

在200℃和0.95～7.70GPa下天然斜绿泥石的拉曼光谱特征

在200℃,0.95-7.70 GPa下,利用激光拉曼光谱技术研究了天然斜绿泥石晶体结构随压力的变化。在200℃,斜绿泥石481和786 cm-1谱峰随压力增加有规律地向高频方向偏移,拉曼位移（N,cm-1）与压力（P,GPa）的线性关系分别为：N=11.136P＋482.6（R2=0.987 4）和N=5.055P＋785.7（R2=0.983 7）。由于四面体层T阳离子与TOT层八面体M阳离子之间产生强烈的排斥作用,使Si—Onb键能增强,导致硅氧四面体层中Si—Onb键伸缩振动的865 cm-1谱峰随压力没有明显的频移。481和786 cm-1谱峰分别对应斜绿泥石晶体结构中M4八面体中M—Obr伸缩振动和Si—Obr—Si伸缩振动,频移说明M—Obr和Si—Obr键长缩短。在实验条件下绿泥石没有发生相变。研究结果说明,在某些冷俯冲带,绿泥石至少在80-90 km深部可能稳定存在,绿泥石脱水及其产生的流体可能是俯冲带地震孕育和发生的重要因素。

高压氘氚靶球的制备与拉曼光谱研究

氢同位素的定量分析与监测在能源与环境领域都有着重要的意义。激光拉曼光谱由于其可以无损分析氢同位素分子,已经成为一种重要的方法,在国际热核聚变实验反应堆(ITER)和美国萨凡纳河工厂得到了广泛应用。利用高压充气装置得到了惯性约束聚变(ICF)高压靶丸,并对靶丸内气体进行原位拉曼光谱测量,通过对高压下氘氚混合气体的拉曼光谱进行分析得到了靶丸内气体的成分比例,验证了靶丸充气工艺参数。实验表明,在CCD的积分时间延长到1min时,氘(DD),氘氚(DT)和氚(TT)的测量精度可以达到1%,同时对不同时刻靶丸内气体组分的拉曼光谱进行测量,实验结果表明在氘氚渗透和氚衰变两者共同作用下,靶丸内总气体压力随时间不断下降,但是气体组成基本不发生变化。

流体包裹体压力计研究之二：高温高压下碳氢化合物的拉曼光谱

在温度23～315℃、压力高达近2000MPa 下用金刚石压腔下研究了正庚烷、环己烷及其混合物的拉曼光谱特征。结果表明:环己烷和正庚烷混合,只是改变了环己烷及正庚烷的平均 C-H 伸缩振动的拉曼位移,但是并不影响其 P-△■关系式。另外,经过数据拟合,得到了平均 C-H 伸缩振动的拉曼位移与压力的关系为:P=78.21(△■)+71.56。该公式可以用来作为流体包裹体尤其是油气包裹体的压力计。

流体包裹体压力计研究之一:高温高压下Na_2SO_4溶液的拉曼光谱

用金刚石压腔研究了Na2S04溶液在温度30—400℃、压力90—2400MPa条件下的拉曼光谱特征。结果表明：温度相同时，SO4^2-的对称伸缩振动随压力增大向高频方向偏移；而在压力基本相同时，随温度升高则向低频方向偏移。经过数据拟合得到了SO4^2-对称伸缩振动的拉曼位移与温度、压力的关系为：ρ=190.44△vp＋0．0027t^2＋2．9019t-111．68。该公式可以用来作为流体包裹体的压力计。

高压下金红石的拉曼光谱分析

常温下利用金刚石压腔装置(DAC)对金红石加压至40GPa,进行拉曼光谱的原位分析。发现压力约为13GPa时。金红石结构转变为斜锆石结构(ZrO2)。21．1GPa相变完全。直至实验最高压力,没有进一步相变出现。在卸压中,斜锆石结构转变为α-PbO2结构。实验压力通过红宝石用拉曼光谱测压的计算方法确定,快速方便。