CeO_2纳米八面体高压结构相变的Raman研究(英文)

利用高压原位拉曼光谱技术研究了非静水条件对CeO2纳米八面体高压结构相变的重压影响。研究表明:在非静水条件下(无传压介质),当压力达到26 GPa时,CeO2纳米八面体发生由立方萤石型结构到正交α-PbCl2型结构的可逆结构相变,相变压力低于相应的体材料(30 GPa)。相反,在准静水压条件下,CeO2纳米八面体的相变压力为33 GPa,高于其体材料。研究表明,实验条件对CeO2纳米八面体结构稳定性具有重要影响。     

超高压下碘的结构相变

 采用DAC高压X光技术，在320 GPa压力下，对碘进行了结构相变的研究。用耐腐蚀材料Mo作封垫，在室温和无保护气氛下装样。采用Mo内标和红宝石荧光测量进行压力校准。结果表明，在21 GPa时，开始发生结构相变，由面心正交相（Ⅰ相），转变为体心正交相（Ⅱ相），体积缩小2%左右。在21~25 GPa之间为两相共存区；在25 GPa以上完全转变为新的高压单相（Ⅱ相）。此相变为可逆相变。     

纳米硫化锌球壳的高压相变研究

 采用同步辐射能量色散X射线衍射（EDEX）技术和金刚石对顶砧高压装置,对纳米硫化锌球壳进行了原位高压X射线衍射实验。最高压力达33.3 GPa。常压下纳米硫化锌球壳为纤锌矿结构和闪锌矿结构共存的混相结构。压力达到11.2 GPa时,纳米硫化锌空心球中的纤锌矿结构全部转变为闪锌矿结构。压力达到16.0 GPa时,发生了由闪锌矿结构向岩盐矿结构的相变,在17.5 GPa和21.0 GPa时分别出现未知峰,33.3 GPa时基本完全转变为岩盐矿结构。两个相变均为可逆相变。     

(111)轴向锑化铟单晶冲击相变研究

 利用气体炮加载方法研究了(111)轴向锑化铟（InSb）单晶的冲击相变以及剪力对冲击相变的影响。冲击加载应力为1.75~3.80 GPa。实验得到，InSb单晶相变的起始应力由静高压时的2.3 GPa下降到1.727 GPa，最大体积变化率为ΔV/V₀＝15.31%，对应的最大剪力为0.681 GPa，剪力水平为83%左右，相变平均静水压力由静高压时的2.3 GPa，下降到0.823 GPa。研究表明，剪力对锑化铟单晶相变的诱发水平有重大影响。     

三聚氰胺(C_3N_6H_6)的高压Raman与压致结构相变研究

本文在8 7GPa压力范围内研究了三聚氰胺(C3N6H6)的高压原位Raman光谱。通过内、外Raman活性模的压致效应,发现在1 5GPa和6 0GPa压力下该分子晶体发生了压致结构相变。用空间群相关原理确认在1 5GPa压力下它从单斜相转变为三斜相;在6 0GPa压力下又发生了另一次结构相变。然后在室温高压条件下对三聚氰胺进行了原位同步辐射能量散射x-ray衍射实验(EDXD),在14 7GPa压力范围内,观察到常压下为单斜晶系的三聚氰胺经历了两次压致结构相变。在1 3GPa下,三聚氰胺分子晶体从单斜相转变为三斜相;在8 2GPa又转变为正交相。本实验结果为利用三聚氰胺碳氮有机分子晶体高温高压合成超硬C3N4共价晶体的研究提供了重要信息。     

MnF2的高压Raman光谱研究

 本文首次报道了在0~3.21 GPa压力范围内MnF₂的高压Raman光谱，结果表明压力在1.32 GPa附近，MnF₂发生了一次结构相变，晶胞中氟原子构成的八面体没有解体。在3.21 GPa下，Raman谱带消失，表明又有一次结构相变发生。     

高压诱致的反式联苯乙烯酮结构相变与化学反应

 利用金刚石对顶砧（DAC）高压装置在室温下对反式联苯乙烯酮（Trans, Trans-Dibenzylideneacetone）分子晶体进行了高压拉曼谱、荧光光谱和能量色散X射线衍射（EDXRD）研究。结果表明,在压力为1.0~1.3 GPa时,反式联苯乙烯酮发生了晶体—晶体的结构相变,同时开始伴随有压力诱导的化学反应,反应完成的压力为6.5 GPa。高压X射线研究表明,这次相变有新的共价键产生,可能的化学变化过程是,C＝C双键打开再与相邻的分子结合生成新的共价键。在压力大约为11 GPa时,反式联苯乙烯酮分子晶体再次发生了晶体的结构相变。新产生的物质在卸压后依然保持稳定。     

Hf-C体系的高压结构预测及电子性质第一性原理模拟

本论文中, 采用晶体结构预测软件USPEX结合第一性原理方法全面地搜索了Hf-C体系在高压下的晶体结构, 预测得到了两种新的化合物及HfC在高压下的相变路径. 压力低于100 GPa 时, 除了常压下的结构HfC, Hf₃C₂, Hf₆C₅, 并没有得到新的热力学稳定结构. 在200 GPa时, 预测得到了一种新化合物——Hf₂C, 空间群为I4/m; 且HfC的结构发生了相变, 空间群由Fm3m变为C2/m. 在300 GPa时, 预测得到了另一种新化合物——HfC₂, 空间群为Immm. 而在400 GPa时, HfC的结构再次发生相变, 空间群为Pnma. 通过能量计算, 得到了Hf-C体系的组分-压力相图: 在压力分别低于15.5 GPa和37.7 GPa时, Hf₃C₂和Hf₆C₅是稳定的; 压力分别大于102.5 GPa和215.5 GPa时, Hf₂C和HfC₂变成稳定化合物; HfC的相变路径为Fm3m→C2/m→Pnma, 相变压力分别为185.5 GPa 和322 GPa. 经结构优化后, 得到了这四种高压新结构的晶体学数据, 如晶格常数、原子位置等, 并分析了其结构特点. 对于Hf-C 体系中的高压热力学稳定结构, 分别计算了其弹性性质和声子谱曲线, 证明是力学稳定和晶格动力学稳定的. 采用第一性原理软件VASP模拟高压结构的能带结构、态密度、电子局域函数和Bader 电荷分析, 发现HfC(C2/m, Pnma结构), Hf₂C 和HfC₂ 中Hf-C 键具有强共价性、弱金属性和离子性, 且C-C 间存在共价作用.     

高压下岩盐矿和单斜结构AgCl的电子行为

 利用基于密度泛函理论的赝势平面波方法，计算了AgCl在高压下的结构行为和电子性质，交换关联函数采用广义梯度近似（GGA）。通过比较焓随压力的变化关系，从理论上确定了AgCl从岩盐矿结构相变到单斜结构的转变压强。预测了这两种结构在布里渊区中的价带顶和导带底的位置，结果表明：盐岩矿和单斜结构的AgCl都是具有间接带隙的半导体。还计算了这两种结构的带隙和电子态密度随压强的变化情况，发现在这两种结构相变之前都不会发生金属化转变。电荷转移研究发现，随着压强的增加，Ag原子和Cl原子之间成键的共价性增强，离子性减弱。     

PbWO_4微晶高压结构相变的Raman光谱研究

本文利用溶剂热方法合成出具有锥形结构的四方白钨矿相PbWO4微晶,并结合金刚石对顶砧压机,利用Raman光谱手段研究了其在22GPa压力下的结构变化。结果发现,在大约4.2GPa,发生了向单斜结构PbWO4-Ш相的局部转变。随着压力继续增大至7GPa,又发现了向亚稳单斜结构的褐钇铌矿相的转变。大约13.2GPa后,亚稳相褐钇铌矿结构也转变为更为致密的PbWO4-Ш相。该相变过程为可逆相变,卸压后恢复为白钨矿结构。     

氧流量对热蒸发CVD法生长β-Ga2O3纳米材料的结构及发光特性的影响

用热蒸发CVD法制备了β-Ga₂O₃纳米材料, 并用光致发光(PL)方法研究了其发光特性. Ｘ射线衍射分析显示, 产物为单斜结构的β-Ga₂O₃. 扫描电子显微镜测试表明: 在较小氧流量条件下制备的产物为β-Ga₂O₃纳米带, 宽度小于100nm, 长度有几微米; 较大氧流量时制备出β-Ga₂O₃纳米晶粒结构, 晶粒尺度在80—15 关键词： 光致发光 氧流量 纳米结构 2O₃')" href="#">Ga₂O₃     

High-pressure effect on inverse spinel LiCuVO4:X-ray diffraction and Raman scattering

The effect of external quasi-hydrostatic pressure on the inverse spinel structure of LiCuVO 4 was studied in this paper. High-pressure synchrotron X-ray diffraction and Raman spectroscopy measurements were carried out at room temperature up to 35.7 and 40.3 GPa, respectively. At a pressure of about 20 GPa, both Raman spectra and X-ray diffraction results indicate that LiCuVO4 was transformed into a monoclinic phase, which remained stable up to at least 35.7 GPa. Upon release of pressure, the high-pressure phase returned to the initial phase. The pressure dependence of the volume of low pressure orthorhombic phase and high-pressure monoclinic phase were described by a second-order Birch-Murnaghan equation of state, which yielded bulk modulus values of B 0 = 197(5) and 232(8) GPa, respectively. The results support the empirical suggestion that the oxide spinels have similar bulk modulus around 200 GPa.     

Structural Transition of Gd2O3：Eu Induced by High Pressure

The structural transition of bulk and uano-size Gd2O3：Eu are studied by high pressure energy disperse x-ray diffraction （XRD） and high pressure photoluminescence. Our results show that in spite of different size of Gd2O3 particles, the cubic structure turns into a possible hexagonal one above 13.4 GPa. When the pressure is released, the sample reverses to the monoclinic structure. No cubic structure presents in the released samples. That is to say, the compression and relaxation of the sample leads to the cubic Gd2O3：Eu then turns into the monoclinic one.     

Diamond anvil cell syntheses and compressibility studies of the spinel-structured gallium oxonitride

The formation conditions of cubic spinel-structured gallium oxonitride have been investigated in situ under high-pressure/high-temperature conditions using a laser-heated diamond anvil cell. As starting materials, a mixture of the end members w-GaN/β-Ga₂O₃ in a molar ratio of 3:2 and a gallium oxonitride ceramic derived during pyrolysis from the metallo-organic precursor (Ga(O^tBu)₂NMe₂)₂ were used. In the mixture of the end members, spinel-structured gallium oxonitride starts crystallizing at a pressure of 3 GPa and at a temperature of about 1300 °C. The precursor-derived ceramic with predefined bondings reacted completely to the spinel phase, without by-products, at a pressure of 0.7 GPa. For the spinel-structured gallium oxonitride we determined a bulk modulus K of 216(7) GPa using a fixed value of 4 for K′. The spinel-structured gallium oxonitride exhibits a cell volume of 552.9(5) ų at ambient pressure.     

High pressure studies up to 50GPa of CuO

Abstract

Copper oxide has been studied at high pressure up to 50 GPa. A monoclinic structure was compatible with the measurements at all pressures, and no phase change was observed. A bulk modulus, B₀, = 98 GPa, and its pressure derivative B′₀ = 5.6 was obtained.     

Structural phase transitions of tellurium nanoplates under pressure

In situ high-pressure angle dispersive x-ray diffraction experiments using synchrotron radiation on Te nanoplates were carried out with a diamond anvil cell at room temperature. The results show that Te-I with a trigonal structure transforms to triclinic Te-II at about 4.9 GPa, Te-II transforms to monoclinic Te-III at about 8.0 GPa, Te-III turns to rhombohedral Te-IV at about 23.8 GPa, and Te-IV changes to body centered cubic Te-V at 27.6 GPa. The bulk moduli B0 of Te nanoplates are higher than those of Te bulk materials.     

Structural phase transitions in yttrium under ultrahigh pressures

X-ray diffraction studies were carried out on the rare earth metal yttrium up to 177?GPa in a diamond anvil cell at room temperature. Yttrium was compressed to 37% of its initial volume at the highest pressure. The rare earth crystal structure sequence hcp?→?Sm?type?→?dhcp?→?mixed(dhcp?+?fcc)?→?distorted fcc (dfcc) is observed in yttrium below 50?GPa. The dfcc (hR24) phase has been observed to persist in the pressure range of 50-95?GPa. A structural transition from dfcc to a low symmetry phase has been observed in yttrium at 99?±?4?GPa with a volume change of -?2.6%. This low symmetry phase has been identified as a monoclinic C2/m phase, which has also been observed in other rare earth elements under high pressures. The appearance of this low symmetry monoclinic phase in yttrium shows that its electronic structure under extreme conditions resembles that of heavy rare earth metals, with a significant increase in d-band character of the valence electrons and possibly some f-electron states near the Fermi level.     

Evidence of a pressure-induced metallization process in monoclinic VO2

Raman and combined infrared transmission and reflectivity measurements were carried out at room temperature (RT) on monoclinic VO2 over the 0-19 GPa and 0-14 GPa pressure ranges. Both lattice dynamics and optical gap show a remarkable stability up to P* approximately 10 GPa whereas subtle modifications of V ion arrangements within the monoclinic lattice, together with the onset of a metallization process via band gap filling, are observed for P >P*. Differently from P=0, where the VO2 metallic phase is found only in conjunction with the rutile structure above 340 K, a new RT metallic phase within a monoclinic structure appears accessible in the high pressure regime.     

富硼稀土硼化物NdB6的高温高压合成

 提出了一种在高温高压极端条件下合成富硼稀土硼化物NdB₆的新方法，即以稀土氧化物Nd₂O₃为钕源与单质硼反应的方法获得了稀土六硼化物NdB₆。并对合成产物进行了粉末X射线衍射分析。结果表明在配比为Nd：B＝1：6时，压力为4.0 GPa、温度为1 600 ℃、反应时间为15 min的条件下，获得了单相性非常好的NdB₆。高温高压合成NdB₆方法具有反应条件易达到、合成时间短、反应产物单相性好等优点。其XRD结果表明该合成产物为立方结构，晶格常数为a＝0.417 nm。     

Substitutional alloy of Bi and Te at high pressure

Being a best known thermoelectric material and a topological insulator at ambient condition, magic bismuth telluride (Bi2Te3) under pressure transforms into several superconducting phases, whose structures remain unsolved for decades. Here, we have solved the two long-puzzling low high-pressure phases as seven- and eightfold monoclinic structures, respectively, through particle-swarm optimization technique on crystal structure prediction. Above 14.4 GPa, we experimentally discovered that Bi2Te3 unexpectedly develops into a Bi-Te substitutional alloy by adopting a body-centered cubic disordered structure stable at least up to 52.1 GPa. The continuously monoclinic distortion leads to the ultimate formation of the Bi-Te alloy, which is attributed to the Bi→Te charge transfer under pressure. Our research provides a route to find alloys made of nonmetallic elements for a variety of applications.