超导体MgB_2成相过程及试验检验

Phase Formation Process and Test of Superconductor MgB_2

粉末反应中MgB2成相过程可分三步完成:两种粉粒由于热运动接触碰撞,做反相微幅受迫振动,形成MgB2成相区;两个硼原子接近,价轨道发生sp2杂化,反应生成B2,镁原子的两个3s价电子自旋相反且成对填入B2的π轨道形成π键生成MgB2,此即MgB2初始晶核。初始晶核有不对称的电场分布和四个外露半满杂化电子轨道;初始晶核分别沿a和c三个轴六个方向接近反应,生长成单晶晶粒。晶粒表面的外露半满杂化电子轨道、镁离子和电子的局域电场可能将相邻晶粒中的晶格周期性接通,形成库伯对穿过晶粒界面的通道;不同晶面中的两种化学键可能导致两种费米分布、两种库伯对和双能隙。利用初始晶核顺磁性和晶粒表面局域电子,对成相过程可做进一步试验检验。

Phase formation process of superconductor MgB2 may be completed through three steps in powder reaction.Firstly,two kinds of powder particles contact and vibrate with opposite phase to generate phase formation region of MgB2 due to thermal motion.Secondly,two boron atoms near and react to generate B2 with sp2 hybrid obits,two valence electrons of magnesium atom fill in pair π orbit of B2 to form π bond and to generate MgB2,this is initial crystal nucleus of MgB2 with four exposed half-filled hybrid orbits and an asymmetric electric field distribution;Thirdly,initial crystal nuclei contact and react along the six directions of a-axis and c-axis to grow into crystal grains.Lattice periodicity in adjacent crystal grains may be connected by exposed half-filled hybrid orbits and local electric fields of magnesium ions and electrons on the surface of the grains to form channel of Cooper pairs penetrating the interface.Two kinds of Fermi distributions,two kinds of Cooper pairs and dual-energy gap may be formed by two kinds of chemical bonds in different crystal planes.Phase formation process could be tested by using the paramagnetism of initial crystal nucleus and spin resonance of the local electrons.