籽晶{100}面形状对高温高压合成金刚石大单晶的影响

选用不同形状的{100}金刚石籽晶面,以NiMnCo合金为触媒,利用温度梯度法在压力为5.5 GPa、温度为1260～1300℃的条件下,合成Ib型金刚石大单晶。通过光学显微镜和电子显微镜对晶体的形貌进行表征。研究发现,将合成籽晶的{100}晶面切割成不同形状,只会令晶体的长宽比发生改变,晶体并不会因籽晶形状的改变而偏离{100}晶体的正常形貌。晶体的合成质量受到籽晶长宽比的影响:在籽晶长宽比较小的情况下,晶体的合成质量能够得到保证;但当籽晶长宽比过大时,合成晶体的下表面出现较多缺陷。关于籽晶形状对晶体生长情况影响的研究,揭示了籽晶形状与合成晶体形貌之间的关系,有利于更深入理解晶体的生长过程和外延生长机理,对于今后合成不同形貌的金刚石具有借鉴意义。同时此项研究有助于扩大籽晶的选取范围,降低籽晶的选择难度,提升工业级金刚石的利用率,为合成金刚石大单晶的籽晶选取提供了技术支持。     

Reaction mechanism of metal and pyrite under high-pressure and high-temperature conditions and improvement of the properties

Pyrite tailings are the main cause of acid mine wastewater. We propose an idea to more effectively use pyrite, and it is modified by exploiting the reducibility of metal represented by Al under high-pressure and high-temperature (HPHT) conditions. Upon increasing the Al addition, the conductivity of pyrite is effectively improved, which is nearly 734 times higher than that of unmodified pyrite at room temperature. First-principles calculations are used to determine the influence of a high pressure on the pyrite lattice. The high pressure increases the thermal stability of pyrite, reduces pyrite to high-conductivity Fe₇S₈ (pyrrhotite) by Al. Through hardness and density tests the influence of Al addition on the hardness and toughness of samples is explored. Finally we discuss the possibility of using other metal-reducing agents to improve the properties of pyrite.     

Utilizing of high-pressure high-temperature synthesis to enhance the thermoelectric properties of Zn0.98Al0.02O with excellent electrical properties

The temperature in the high-pressure high-temperature(HPHT) synthesis is optimized to enhance the thermoelectric properties of high-density Zn O ceramic, Zn_0.98Al_0.02O. X-ray diffraction, scanning electron microscopy, and transmission electron microscopy show that HPHT can be utilized to control the crystal structure and relative density of the material.High pressure can be utilized to change the energy band structure of the samples via changing the lattice constant of samples, which decreases the thermal conductivity due to the formation of a multi-scale hierarchical structure and defects. The electrical conductivity of the material reaches 6×10⁴ S/m at 373 K, and all doped samples behave as n-type semiconductors. The highest power factor(6.42 μW·cm^-1·K^-2) and dimensionless figure of merit(z T = 0.09) are obtained when Zn_0.98Al_0.02O is produced at 973 K using HPHT, which is superior to previously reported power factors for similar materials at the same temperature. Hall measurements indicate a high carrier concentration, which is the reason for the enhanced electrical performance.