超高压下CsBr的结构与相变

 采用金刚石对顶压砧高压装置（DAC）、同步辐射X光源和能散法，对CsBr粉末样品进行了原位高压X光衍射实验，最高压力达115 GPa。观测到在53 GPa左右压力下，CsBr的最强衍射峰(110)劈裂成两个峰，标志了简单立方结构向四方结构的转变；在0至最高压力范围内（相应于V/V₀为1至0.463）测量了晶轴比c/a；在115 GPa内未观测到样品的金属化现象。     

C60高压X射线衍射研究

 采用同步辐射X光源和能量色散法对高纯C₆₀粉末样品进行高压原位X光衍射实验。由金刚石对顶压砧高压装置（DAC）产生高压,用已知状态方程的Pt粉末作内标,由Pt的衍射数据确定样品压力,最高压力达30 GPa。实验结果表明：室温常压下原始C₆₀样品为面心立方结构,晶格常数a=1.420 86 nm。高压下C₆₀的结构有所变化：从p=13.7 GPa开始,(311)线发生劈裂,形成低对称相;随着压力增加,衍射线逐渐变宽,强度逐渐变弱,压力超过25 GPa,衍射背底隆起,C₆₀开始转化成非晶相;在30 GPa左右,衍射线条完全消失,标志着向非晶相转化过程的完成。人们也对C₆₀样品不同压力的高压“淬火”相进行了X光衍射实验。采用非静水压的装样方式,最高压力达44 GPa,结果在30 GPa以上,C₆₀也转变为非晶相。最后我们对C₆₀晶体的压致非晶化现象进行了初步的讨论。     

非静水压下材料强度对压力标定的影响

采用金刚石对顶砧压腔和同步辐射X射线衍射技术研究了非静水压下材料强度对压力标定的影响。实验中,在同一个高压腔中用Pt和Au作为压标进行压力标定比较。Pt标定腔内压力,分别将Au与β-SiC和NaCl粉末混合,压力均加载到50GPa。结果表明:当使用β-SiC作为样品材料时,Pt标定的压力和Au标定的压力出现了比较大的差别;当使用NaCl作为样品材料时,Pt标定的压力和Au标定的压力十分接近。说明在非静水压下,样品材料强度对于压力标定有很大的影响。     

层状钙钛矿结构锰氧化物Ca3Mn2O 7的压致结构相变

采用金刚石压砧高压装置（DAC）,对层状钙钛矿结构锰氧化物Ca3Mn2O7的粉末样品进行了高压能散X射线衍射实验。实验结果表明,在0－35GPa压力范围内,Ca3Mn2O7晶体结构发生了两次相变。在1．3GPa左右,由原来的四方相转变为正交相,在9．5GPa左右,又由正交相向新的四方相转变。     

高压对钴酸锂的晶体结构和离子导电率的影响

采用金刚石对顶砧(DAC)高压产生装置,结合同步辐射X射线衍射(XRD),对钴酸锂(LiCoO2)粉末样品进行室温下原位高压X射线衍射实验,最高压强达到20.3GPa。研究结果表明:在20.3GPa下,LiCoO2的晶体结构非常稳定,并没有发生结构相变;在20.3GPa范围内测量了晶体沿不同晶轴a、c方向的压缩比,发现LiCoO2沿c轴方向的压缩率是沿a轴方向的4.5倍;使用二阶Birch-Murnagha方程拟合出钴酸锂样品的等温状态方程。另外还采用高压原位交流阻抗谱技术(EIS),测量了不同压强下钴酸锂中锂离子导电率,最高压强达到16.8GPa时,发现在实验的压强范围内,随着压强的增加,离子导电率减小。最后将高压下锂离子的电导率与钴酸锂的晶体结构进行联系,进一步阐述了高压下钴酸锂的微观结构和电学性能之间的关系。     

高压下两种8—羟基喹啉络合物的发光行为和结构变化

测定了在高压条件下两种金属(钙和锌）的8-羟基喹啉络合物的晶体粉末样品的发光行为和原位X光衍射光谱．结果表明,压力对其发光性质产生极大的影响．随着压力的增加,8—羟基喹啉钙的发光强度在3GPa以内时大大增加,随后发光强度快速下降．到7GPa左右时几乎为零,而8-羟基喹啉锌的发光强度随压力的增加而逐渐降低,到7GPa左右时约为常压的10％。高压下的原位X光衍射结果表明,8—羟基喹啉锌的晶体在3—4GPa开始发生非品化相变,在7GPa时该非晶化相变完成,样品的x光衍射完全消失．而8—羟基喹啉锌在压力的作用下(至16GPa)没有发生明显的相变。     

高压下碳纳米管的X射线衍射研究

 用同步辐射原位高压能散X射线衍射技术,对碳纳米管进行了结构和物性的研究,压力达50.7 GPa。在室温常压下,碳纳米管的结构和石墨的hcp结构相似,其(002)衍射线的面间距为d₀₀₂=0.340 4 nm,(100)衍射线的面间距为d₁₀₀=0.211 6 nm。从高压X射线衍射实验看到,当压力升到8 GPa以上时,(002)线变宽变弱,碳纳米管部分非晶化。而当压力从10 GPa或20 GPa卸压至零时,(002)线部分恢复。但当压力升高至最高压力50.7 GPa时,碳纳米管完全非晶化,而且这个非晶化相变是不可逆的。用Birch-Murnaghan方程拟合实验数据,得到体弹模量为K₀=(54.3±3.2)GPa（当K′₀=4.0时）。     

石墨相C_3N_4压致结构相变研究

将有机物三聚氰胺(C3N6H6)高温热解,得到了石墨相C3N4(g-C3N4)。利用同步辐射X射线衍射和金刚石对顶砧(DAC)高压技术,在室温下对g-C3N4进行了结构变化研究。实验结果表明,在16.57 GPa压力范围内,g-C3N4发生了压致结构相变,在6.6 GPa压力下,晶体结构由原来的石墨相转变为三斜相。使用Birch-Murnagha等温状态方程拟合出了样品的等温状态方程。     

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。     

巨磁阻材料Sr2CrWO6高压下的结构稳定性和电学特性

 采用金刚石压砧高压装置，研究了双钙钛矿结构化合物Sr₂CrWO₆在室温下、34.5 GPa压力内的同步辐射X射线衍射谱，发现在9.6 GPa的压力点样品的结构有所变化。结合室温下20 GPa内电阻和电容随压力的变化，证明样品在9 GPa附近发生了晶体结构相变，而在2~5 GPa的压力范围内样品发生了电子结构相变。     

Pressure-Effect on Anatase Titanium Dioxide

Pressure-induced phase transition of anatase titanium dioxide was investigated by Raman, absorption spectroscopy and X-ray diffraction. The change in Raman and absorption spectra with pressure revealed that the transition from anatase to high pressure phase with f -PbO 2 structure (TiO 2 -II) occurred in the pressure range of 4.0-4.6 GPa for a single crystal. The X-ray powder diffraction patterns indicate the presence of superstructural lattice of anatase at pressures more than 3 GPa. The superstructure of anatase disappears on the release of the pressure. A sluggish transition to the high pressure phase is also observed. The anatase coexists with the high pressure phase at 5.2 GPa. The difference in the results between optical spectroscopy (single crystal) and X-ray diffraction (powder) will be due to crystalinity of the sample.     

Evolution of disorder in Zn(CN)2 at high pressure

Zinc cyanide is an interesting negative thermal expansion (NTE) material exhibiting cubic structure at ambient pressure and temperature. We have investigated the structural stability of zinc cyanide under high pressure up to 5.2 GPa by performing X-ray powder diffraction in a diamond anvil cell. Under very low pressure of about 0.6 GPa, the diffraction peaks drastically reduce in intensity, indicating possible onset of disorder in the structure. In this paper, its high pressure structural and compressibility behaviour, bulk modulus and the pressure derivative of bulk modulus are reported.     

Equal compressibility structural phase transition of molybdenum at high pressure

We have studied the high-pressure compression behavior of molybdenum up to 60 GPa by synchrotron radial x-ray diffraction (RXRD) in a diamond anvil cell (DAC). It is found that all diffraction peaks of molybdenum undergo a split at around 27 GPa, and we believe that a phase transition from a body-centered cubic structure to a rhombohedral structure at room pressure has occurred. The slope of pressure-volume curve shows continuity before and after this phase transition, when fitting the pressure-volume curves of the body-centered cubic structure at low pressure and the rhombohedral structure at high pressure. A bulk modulus of 261.3 (2.7) GPa and a first-order derivative of the bulk modulus of 4.15 (0.14) are obtained by using the nonhydrostatic compression data at the angle ψ = 54.7° between the diffracting plane normal and stress axis.     

Pressure-induced phase transitions in CaB6 by means of XRD and resistance measurement

High pressure behavior of CaB₆ with cubic crystal structure is investigated by means of energy dispersive X-ray diffraction and by employing in situ resistance measurement in a diamond anvil cell. Two newcome high pressure phase transitions are found with pressure ranging from ambient to 26 GPa. The first one at 12 GPa is a structural phase transition from CsCl-type structure to orthogonal structure, which is reflected by both the X-ray diffraction and the resistance variation. The other one at 3.7 GPa is suggested to be an electronic transition, which is observed only in resistance measurement. The diffraction pattern recovered while the pressure is released to 0 GPa with a pressure hysteresis over 11 GPa, which implies the reversibility of the two phase transitions. Bulk moduli of the cubic and orthogonal phases are estimated by fitting the data to a Brich-Murnaghan equation of state equal to 169.9 and 48.2 GPa, respectively.     

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。     

Exploring the compression behavior of HP-BiNbO_4 under high pressure

In the present work, a third form, the so-called HP-BiNbO_4 synthesized at high pressure and high temperature is investigated with the in-situ angle-dispersive x-ray diffraction(ADXRD) measurements under high pressure. We explore the compression behavior and phase stability of HP-BiNbO_4. The structure of HP-BiNbO_4 is first determined. The x-ray diffraction data reveal that the structure HP-BiNbO_4 is stable under pressures up to 24.1 GPa. The ADXRD data yield a bulk modulus K_o = 185(7) GPa with a pressure derivative K_o'= 2.9(0.8). Furthermore, the data are compared with those of other ABO_4 compounds. The results show that the bulk modulus of HP-BiNbO_4(about 185 GPa) is slightly higher than that of tetragonal BiVO_4 and significantly greater than those of the tungstates and molybdates.     

High pressure investigations on amorphous selenium

We report the diamond anvil cell (DAC) high pressure powder X-ray diffraction studies on amorphous selenium (a-Se) under truly hydrostatic pressure condition up to 20 GPa. Amorphous selenium exhibits a sharp and irreversible transition to a hexagonal structure at 10.6 ± 0.1 GPa. It is also known that metallization occurs in a-Se around this pressure. Some plausible arguments are provided to suggest that the amorphous to crystalline transition may be driven by metallization.