硫化铁的两个电导率相关的相变

 由于X射线对高级相变和电子相变不够敏感,致使很多物质的相变和新的性质被忽略。对物质电阻的变化进行分析可以很好地弥补这一缺陷。通过金刚石对顶砧上原位电阻测量方法,在0~88.7 GPa的压强范围内,在300~443 K的温度条件下,基于范德堡法电阻测量原理,对硫化铁的电导率进行了测量。通过对电导率的分析发现,在零压、温度为408 K的条件下,硫化铁转变成了NiAs结构相。在34.7 GPa和61.3 GPa压强处发现了两个新的突变点,为了印证这两处相变的可靠性,分别测量了在不同压强下样品电导率随温度的变化情况。     

CdSe在高压下的电学性质及相变

 利用在金刚石压砧上集成的微电路,原位测量了CdSe多晶粉末在温度为300~450 K、压力达到23 GPa时电阻率随温度和压力的变化关系。实验结果表明：在加压过程中,电阻率在2.6 GPa压力时出现的异常改变,对应着CdSe从纤锌矿向岩盐矿结构的转变,而在6.0、9.8、17.0 GPa等压力处出现的电阻率异常,则是由CdSe中的电子结构的变化所引起的;在卸压过程中,只在约14.0和3.0 GPa压力下观察到了两个电阻率异常点。通过对电阻率随压力变化曲线的模拟,得出了CdSe高压相的带隙随压力的变化关系,据此预测CdSe金属化的压力应在70~100 GPa之间。变温实验结果表明,在实验的温度和压力范围内,CdSe的电阻率均随温度的增加而升高。     

Pressure-Induced Metallization and Structural Phase Transition in the Quasi-One-Dimensional TlFeSe_2

We report a comprehensive high-pressure study on the monoclinic TIFeSe_2 single crystal,which is an antiferromagnetic jnsulator with quasi-one-dimensional crystal structure at ambient pressure.It is found that TIFeSe_2 undergoes a pressure-induced structural transformation from the monoclinic phase to an orthorhombic structure above P_c≈13 GPa,accompanied with a large volume collapse of ΔV/V_0=8.3%.In the low-pressure monoclinic phase,the insulating state is easily metallized at pressures above 2 GPa;while possible superconductivity with T_c~(onset)～2 K is found to emerge above 30 GPa in the high-pressure phase.Such a great tunability of TIFeSe_2 under pressure indicates that the ternary AFeSe_2 system(A=Tl,K,Cs,Rb) should be taken as an important platform for explorations of interesting phenomena such as insulator-metal transition,dimensionality crossover,and superconductivity.     

Metallization of Cu3N Semiconductor under High Pressure

Using the four-probe method, we investigate the electrical conductivity of Cu3N under high pressure with the diamond anvil cell. Cu3N is a semiconductor at ambient pressure showing a band gap about l eV. With the application of quasi-hydrostatic pressures, its resistance decreases dramatically over five orders of magnitude from ambient to 9 GPa. The compound became a metal at pressure about 5.5 GPa, which is in well agreement with the recent first principle calculation.     

Raman Scattering Spectroscopy of Phase Transition in n-Pentadecane under High Temperature and High Pressure

The Raman spectroscopy of n-pentadecane is investigated in a moissanite anvil cell at normal temperatures and a diamond anvil cell under pressure to about 3000MPa and at temperature from 298 to 573K. Result indicates that at room temperature the vibration modes, assigned to the symmetric and asymmetric stretching of CH3 and CH2 stretching, shift to higher frequency and display a pressure dependent quasi-linear curve. A liquid-solid phase transition appears at a pressure of 150 MPa. The high temperature solidus line of n-pentadecane follows a quadratic function of P = 0.02369T^2 - 9.117T ＋ 725.58, in agreement with previous conclusion derived from studies of other hydrocarbons. Upon phase transition, fitting the experimental data obtained in a temperature range of 283 553 K to the Clausius-Clapeyron equation allows one to define the thermodynamic parameters of n-pentadecane of dP/dT = 0.04738T - 9.117.     

聚晶金刚石复合片超高压烧结过程的实验研究

 采用X射线衍射（XRD）分析、扫描电子显微镜（SEM）和能谱分析（EDX）等方法,对在压力5.6 GPa、温度1 460 ℃条件下,加热时间分别为2、3、4、6、8、10 min的聚晶金刚石复合片（PDC）样品进行了分析。结果表明：PDC的烧结经历了金刚石的石墨化过程,而且在烧结过程中金刚石层表面的XRD图谱出现了WC衍射峰,强度由弱到强,再由强到弱,直至消失;进一步的研究发现,PDC中助烧结剂Co的晶格常数因C和W原子的固溶会变大,并随PDC加热时间的延长出现一个峰值;从硬质合金基体扩散到金刚石层的Co由于扩散通道各异、所受阻力不同,使得其分布不均匀。     

Structural Stability of CaCuMn6O12 under High Pressure and Low Temperature

In situ high pressure energy-dispersive x-ray synchrotron radiation diffraction and resistance experiments are carried out on CaCuMn6O12. Its crystal structure is stable in the measured pressure range. The equation of state of CaCuMn6O12 is obtained from the V/Vo - P relationship （V and Vo are the volumes at pressure P and at atmosphere）. The bulk modulus Bo is calculated based on the Birch-Murnaghan equation. Low temperature x-ray diffraction shows no phase transition occurring down to 160K.     

高空低压低温环境航空发动机燃烧室熄火特性实验

航空发动机高空熄火是非常严重的安全威胁,高空燃烧稳定性与可靠再点火是航空发动机燃烧室的普遍要求.文章介绍了高空低压低温条件下航空发动机燃烧室模拟实验设备方案和调试结果,实现了对地面状态到高空10 km处环境条件的模拟.研究表明,随着高度增加,贫油熄火极限油气比不断增大.地面状态的贫油熄火油气比为0.016,高空10 km条件下,熄火油气比为0.071,增大3倍以上.低压低温环境下,火焰锋面位置不断向喷嘴收缩,燃烧释放热区域缩小到燃油喷嘴头部附近,CH*发光强度不断衰减.在模拟高度4 km时,火焰开始转为淡蓝色,10 km时燃烧室内为淡蓝色火焰,燃烧趋于不稳定.      

高温高压下辉石岩的电导率研究

 利用阻抗谱在1.0~2.0 GPa、温度450~792 K条件下、10⁵~12 Hz的频率范围内,对辉石岩的电导率进行了研究,并且分析了测试频率对电导的影响,结果表明,电导率对频率具有一定的依赖性;在复平面上出现了代表颗粒内部的阻抗弧。辉石岩的激化焓为0.661~0.673 eV,样品中较高的铁含量可能是造成本实验电导率较高的主要原因。     

高温高压下冲击波淬火的锆基大块金属玻璃的相演化过程研究

 采用同步辐射能散X射线衍射技术,研究了高温高压下利用冲击波淬火技术制备的Zr₄₁Ti₁₄Cu_12.5Ni₁₀Be_22.5大块金属玻璃的相演化过程。研究结果发现：在实验压力范围内,在不同压力下试样具有相同的初始析出相Zr₂Be₁₇,但是随后的相演化过程是不同的,根据应用压力的不同,试样的相演化过程可以分为3个不同的区域;另外,试样的晶化温度随着压力的增大而升高,但是在6.0 GPa存在一个突然的下降,在此压力点试样具有不同于其它压力点的相演化过程。相演化过程的不同和晶化温度的突然下降,可能归因于在不同压力下试样具有不同的原子构型。     

镁橄榄石和顽辉石的高温高压合成

 用国产六面顶压机,在温度为1 000～1 500 ℃和压力为2～5 GPa的高温高压条件下,对氧化镁（MgO）和二氧化硅（SiO₂）混合粉末样品进行了处理。通过对所得产物的观察与X射线衍射分析结果表明,在较宽的压力范围内,可以得到镁橄榄石（Mg₂SiO₄）单晶体和顽辉石（MgSiO₃）单晶体。讨论了地幔物质镁橄榄石（Mg₂SiO₄）和顽辉石（MgSiO₃）的生成条件、生长特性及相变关系。     

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。     

高温高压下硬水铝石状态方程研究

 在金刚石压砧装置上,用氧化铝膜作绝热层,借助同步辐射和双面激光加温系统,分析了硬水铝石在高温高压下的结构变化,并分别用理论和实验的方法得出了其结构参数,得到了样品在不同压力温度下的体模量。这对于人们认识和研究地壳结构和地球内部物质的演化具有重要意义。研究发现,在常温和高温时其压缩率有明显不同,在高温高压范围内,其晶格常数和晶胞体积的变化非常接近样品在高压常温下的情况;而在高温低压范围内,情形和常温时有较大差别。在实验过程中并没有发现相变的产生。     

Structural stability and vibrational characteristics of CaB_6 under high pressure

In situ Raman spectroscopy and x-ray diffraction measurements are used to explore the structural stability of CaB_6 at high pressures and room temperature. The results show no evidence of structural phase transitions up to at least 40 GPa.The obtained equation of state with smooth pressure dependencies yields a zero-pressure isothermal bulk modulus B0=170(5) GPa, which agrees well with the previous measurements. The frequency shifts for A_(1g), Eg, and T_(2g) vibrational modes of polycrystalline CaB_6 are obtained with pressure uploading. As the pressure increases, all the vibration modes have smooth monotonic pressure dependence. The Gr¨uneisen parameter of Eg modes is the largest, indicating its largest dependence on the volume of a crystal lattice.     

冷轧低碳钢高压相变组织的透射电镜分析

 对冷轧低碳钢在高压下进行再结晶,用透射电子显微镜（TEM）分析高压相变组织,发现压力可以使再结晶晶粒细化;压力升高,具有体心立方结构的普通低碳钢可形成ε-马氏体,并根据电子衍射花样的计算确定ε-马氏体的晶格参数。     

Phase Transitions in Lead Hafnate under High Pressure

Physics of the Solid State - The effect of hydrostatic pressure on phase transitions in lead hafnate (PbHfO3) has been studied by the methods of X-ray diffraction and X-ray diffuse scattering. The...     

Cubic BN Sintered with A1 under High Temperature and High Pressure

Sintering of cubic boron nitride （cBN） with addition of A1 is carried out in the temperature range 1300-1500℃ and under the pressure 5.5 GPa. When sintered at 1300℃, a weak diffractive peak of hexagonal BN （hBN） is observed in the Al-cBN sample, indicating the transformation from cBN to hBN. No nitrides or borides of A1 are observed, which indicated that A1 does not react with cBN obviously. When the sintering temperature is increased to 1400℃, the diffractive peak of hBN disappears and new phases of A1N and A1B2 are observed, due to reactions between A1 and cBN. When the sintering temperature is further increased to 1500℃, the contents of A1N and A1B2 phases increase and the A1 phase disappears completely.     

高压下纳米尺寸Sr2FeMoO6粉末的结构稳定性和电学特性的研究

 采用高分子网络凝胶法，通过控制其化学反应过程，合成了高纯的多晶纳米级粉末Sr₂FeMoO₆样品A（50 nm）和样品B（100 nm）。对其在高压下的结构稳定性和电学性质进行了研究，并将样品A和样品B的实验结果与已报道的粒度达微米级的块状Sr₂FeMoO₆样品C的实验结果进行了对比。在实验测量范围内，样品A（50 nm）呈现出最大的体弹模量B₀，并在电阻-压力曲线中，电阻下降区域表现出相对较缓的变化率，晶界效应可以用来很好地解释此结果。电学性质测量实验表明，样品在高压下发生了电子结构相变。     

顽火辉石的高温高压同步辐射研究

 采用同步辐射能量色散X射线衍射技术、激光加热技术和金刚石对顶砧（DAC）高压装置,在温度为2 000 K和压力为23 GPa的范围内,对采自地幔二辉橄榄岩中的顽火斜方辉石,进行了原位的高温高压能量色散X射线衍射（EDXRD）测量。实验结果表明：当压力为15.3 GPa、温度为1 600 K时（相当于地球内部410 km处的地震波不连续界面的温压环境）,顽火斜方辉石转变为橄榄石的β相——瓦兹利石（Wadsleyite）相;继续加温加压至2 000 K、23 GPa时（相当于地球内部670 km处的地震波不连续界面的温压环境）,顽火斜方辉石相变为钛铁矿（Ilmenite）结构和钙钛矿（Perovskite）结构的混和相。实验结果进一步证明,在地幔中存在的两个地震波不连续界面是由橄榄石、顽火斜方辉石等矿物的相变引起的。