共查询到20条相似文献,搜索用时 156 毫秒
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研究了制备压力对纳米块状样品La2/3Sr1/3MnO3的结构、磁学和电学性质的影响。结果表明:样品的晶粒尺寸随制备压力的增加而变小,且不同样品的磁电阻效应不同。低场磁电阻效应在整个实验温区都随制备压力的升高而变弱,这主要是由制备压力使样品晶粒界面连接更紧密所导致;T<200 K时,高场磁电阻效应随制备压力的升高而变强,T>200 K时,高场磁电阻效应随制备压力的升高反而变弱,这主要是由制备压力改变样品的晶粒尺寸所引起。 相似文献
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通过对裂解聚吡咙(PMDA-DAB)薄膜导电性环境温度、裂解温度及压力关系的研究表明:其室温导电率随所加压力与裂解温度的升高而增加。电导与温度的依赖行为有赖于裂解温度Tp及所加的压力在Tp<800 ℃时,碳化过程产物能符合三维变程跃迁模型;而在Tp>800 ℃时,石墨化过程产物则比较符合修正的三维变程跃迁模型。最大的导电率是在裂解温度为1 200 ℃的裂解产物上在1.05 GPa压力下获得的,数值约1 000 S/cm,电导与压力的关系能较好地符合所改进的扩展莫特关系。 相似文献
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为了探讨压力对类氢原子结构与性能的影响,本文采用类氢原子关闭在一半径为r0的球壳内的模型,计算其能量与极化率随球壳半径r0与相应压力的变化规律,给出了数值表和相应的曲线。 相似文献
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本文研究了Pd40Ni40P20块状非晶在4 GPa及常压下的晶化过程。得到了时间-温度转变图。结果表明:高压下样品的晶化温度明显升高,压力对原子的长程扩散及相分离熔体的粘性流动均有抑制作用。在接近熔点进行高压退火时,获得了单相过饱和固溶体。其晶体结构为面心立方。 相似文献
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在高温高压条件下,用hBN-LiH和hBN-Li3N-B为初始材料均可以合成出黑色cBN晶体。拉曼光谱测试结果表明,cBN晶体颜色变黑的原因是晶体中多余B原子的存在造成的。在hBN-Li3N-B体系中,晶体内部有明显的三角形阴影形成,表明从晶体表面的中心到顶角间B原子的含量较多,从表面中心到棱边B原子的含量逐渐减少。而在hBN-LiH体系中所得到的晶体颜色从黑色透明直接变成黑色不透明状态,晶体内部没有出现三角形阴影,表明晶体中作为杂质的B原子分布比较均匀。此两种情况说明,B作为杂质原子进入cBN晶体中可以有两种分布情况,一是居中对称分布,二是均匀分布,从晶体的生长环境和自身的排杂能力方面分析了晶体为什么会出现上述现象。 相似文献
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Analysis of Transition Mechanism of Cubic Boron Nitride Single Crystals under High Pressure-High Temperature with Valence Electron Structure Calculation
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The possibilities of hexagonal boron nitride(hBN) and lithium boron nitride(Li_3BN_2) transition into cubic boron nitride(cBN) under synthetic pressure 5.0 GPa and synthetic temperature 1700 K are analyzed with the use of the empirical electron theory of solids and molecules. The relative differences in electron density are calculated for dozens of bi-phase interfaces hBN/cBN, Li_3BN_2/cBN. These relative differences of hBN/cBN are in good agreement with the first order of approximation(10%), while those of Li_3BN_2/cBN are much greater than 10%.This analysis suggests that Li_3BN_2 is impossible to be intermediate phase but is a catalyst and cBN should be directly transformed by hBN. 相似文献
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采用第一性原理研究了CdS的六方纤锌矿(WZ), 立方闪锌矿(ZB) 和岩盐矿(RS)相在高压条件下的相稳定性、 相变点、电子结构以及弹性性能.WZ相与RS 相可以在相应的压强范围内稳定存在, 而ZB相不能稳定存在.压强大于2.18 GPa时, WZ相向RS相发生金属化相变.WZ相中S原子电负性大于Cd, 且电负性差值小于1.7, CdS的WZ相为共价晶体.高压作用下, S原子半径被强烈压缩, 有效核电荷增加, 对层外电子吸引能力提高, 电负性急剧增大, 导致S与Cd的电负性差值大于1.7, CdS的RS相以离子晶体存在. WZ相的C44随压强增加呈下降趋势, 导致WZ相力学不稳定, 并向RS相转变.当压强大于2.18 GPa时, RS相C11, C12随压强增加而增大, 并且C44保持稳定, 说明RS相具有良好的高压稳定性与力学性能.
关键词:
第一性原理
相变
电子结构
弹性性质 相似文献
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利用有效场理论研究了纳米管上双模随机晶场中混合自旋Blume-Capel模型的相变行为。结果表明,系统相变行为与取值概率、晶场强度比值、晶场参数、温度以及外壳层最近邻交换相互作用密切相关。取值概率、晶场强度比值、晶场参数和外壳层最近邻交换相互作用等诸多因素相互竞争,影响系统的一级和二级相变以及临界点。 相似文献
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The transverse electro-optic(EO)modulation system is built based on cubic boron nitride(cBN)single crystals unintentionally doped and synthesized at a high pressure and high temperature.The photoelectric output of the system includes two parts that can be measured respectively and the value of elements in the linear EO tensor of the cBN crystal can be obtained.This method does not need to measure the absolute light intensity.All of the surfaces of the tiny cBN crystals whose hardness is next to the hardest diamonds are{111}planes.The rectangular parallelepiped cBN samples are obtained by cleaving along{110}planes and subsequently grinding and polishing{112}planes of the tiny octahedral cBN flakes.Three identical non-zero elements of the EO tensor of the cBN crystal are measured via two sample configurations,and the measured results are very close,about 3.68 and 3.95 pm/V,respectively,which are larger than the linear EO coefficients of the general III-V compounds. 相似文献
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Abstract Techniques and results of studies on the kinetics and hysteresis of the structural phase transitions in lanthanides under pressures up to 58 GPa and temperatures between 200 K and 520 K are presented. The transformation rates show the same time dependence as for diffusion controlled transitions, however, other interpretations of this time dependence are also possible. Estimates of the 0 K equilibrium transition pressures are derived from the pressure and temperature dependence of the activation free energies A, G. A comparison of critical radius ratios, Rux/R5p for all the regular lanthanides at the various phase transitions shows simple systematics in the high pressure behaviour of the lanthanides. 相似文献
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The features of structural phase transitions that occur under high pressure are studied. The density functional theory is used to calculate the B1–B2 phase transition pressure as a function of the crystal size for small-sized alkali halide crystals. A size effect (an increase in the phase transition pressure as the crystal grain radius decreases) is revealed for the B1–B2 transitions in all halogen compounds except for lithium fluoride, for which the dependence is inverse. 相似文献