The Effect Of HBN Re-crystallized Character On CBN Synthesis And Direct Nucleation And Growth Of CBN

As well known, cubic boron nitride (cBN) is widely used in the region of mechanics, thermology, optics and electronics. Due to its unique physical and chemical property such as its hardness next to diamond, thermal stability (up to 1300℃) as well as the chemical inertness to ferrous metals and its alloy etc, cBN is extensively used in machine industry. Also, cubic boron nitride is the simplestⅢ-V compound semiconductor material. It has the energy gap about 6.4eV, and can be made easily into both P- and N-type with suitable impurity additions. These characteristics make cBN a very promising material for application in high-temperature microelectronic as well as optoelectronic devices. CBN crystal must possess excellent property whether applied in the superhard materials or in the semiconductor. So the synthesis method of cBN crystal is always studied by researchers.Since the cBN was synthesized in our country the growth technology has made great progress. However, the gap in the growth technology of cBN is still lagger than developed country. In recent years, we devoted the basic investigation of cBN crystal all along to develop new growth technology of cBN.In this paper, using hBN which was treated under high pressure and high tempareture as starting material, we concluded the re-crystallization degree of hBN. And then, we investigated the synthesis of cBN using the treated hBN. The results indicated that cBN synthesis condition was affected remarkably. The conclusion was as follow.Three hBN of different initial crystallization were chosen as the researched object, and the trend changed of their crystallization degree was the same under HPHT. The different crystallization degree of hBN affect on synthesis condition was different.1,Under the same temperature and holding same time, with the pressure increasing, the crystallization degree of hBN first increased rapidly, and then decreased slowly.Under the same pressure and holding same time, with the temperature increasing, the crystallization of hBN degree increased gradually.Under the same pressure and the tempearure, with the holding time increasing, the crystallization degree of hBN increased gradually.2,In the synthesis conditions such as temperature, pressure and hold time, the impact of the synthesis temperature is the most significant to hBN crystallization degree, holding time takes second place, and the weakest is the pressure.3,Three hBN of different initial crystallization being compared, the lower the degree of initial crystallization is, the higher the degree of crystallization becomes after the same pretreatment of HPHT experimental conditions.4,After the pretreatment of HPHT conditions, cBN is synthesized easily by low degree of hBN crystallization. On the bases of thermodynamic analysis,we obtained some theoretic formulae. From the physics significance of these formulae we could see that the results are well consistent with experimental data. The conclusion was as follow.1,At the same conditions, the smaller the rk is, the higher the transformation rate will be in system.2,In order to obtain a small critical grain size, it is important to hold a high pressure.3,If we want to obtain a bigger size crystal, we should control the number of cBN nucleation under high temperature and low pressure.4,If we want to improve crystal quality, the region of synthesis should be chosen in high temperature and moderate pressure region.Cubic boron nitride single crystal was synthesized using the mixture compound or element which contains B or N by chemical reaction under high pressure and high temperature. The conclusion was as follow.1,Without any form of the BN in the starting material, cubic boron nitride single crystal was synthesized using the mixture of Li3N-B2O3 or Li3N-B by chemical reaction.2,Because of no form of the BN in the starting material and the synthesis condition being lower than that using Li3N or Li3BN2 as catalyst, cBN was nucleated directly by chemical reactions, and was not the phase transition from sp2-bonded hBN to sp3-bonded cBN.3,CBN crystal has been synthesized under lower condition, and the crystal size exceeded 100μm in short time 4mins. So, the mechanism of crystal growth was a combination effect of the crystal seed which formed in the chemical reactions gravitation and dissolve-precipitate.4,B atom entered into crystal through the way of substituting N vacancy on {111} facet. B atom entered into crystal and changed the crystal color to black.5,Because the B atoms on {111} facet have no vacant bond, B atoms entered into crystal restrain crystal growth along <111> planes. However, the crystal was easy to grow along <100> planes.