Dr. Takashi Taniguchi[National Institute for Materials Science, Japan]

Title: High pressure synthesis of polymorphic phase of Boron Nitride to realize their potentials as super-hard and wide-bandgap materials

Time:  Feb. 26, 2019   15:00-16:00

Place: Conference room 410, HPSTAR (Shanghai)

Host:  Toshimori Sekine

Polycom: 02120004 

Abstract:

Hexagonal boron nitride BN (hBN) and cubic BN (cBN) are known as the representative crystal structures of BN. The former is chemically and thermally stable, and has been widely used as an electrical insulator and heat-resistant materials. The latter, which is a high-density phase, is a super-hard material second only to diamond. In addition to those, wruztite BN (wBN) is also known as other polymorphic phase.   

Among those BN crystals, some progresses in the synthesis of high purity BN crystals were achieved by using Ba-BN as a growth solvent material at high pressure (HP) of 5.5GPa. Band-edge natures (cBN Eg=6.2eV and hBN Eg=6.4eV) were characterized by their optical properties. Then an attractive potential of hBN as a deep ultraviolet (DUV) light emitter and also superior properties as substrate of graphene devices were realized. By using high purity hBN crystal as a starting material, high purity cBN sintered body and also highly oriented wBN crystalline form were obtained under high pressure. Mechanical properties of highly oriented wBN crystals were evaluated by nano-indentation technique showing their next hard properties after cBN.

In this paper, recent studies on BN polymorphic phases obtained at high pressure with respect to impurity control and their function will be reported. The present issue to improve their properties further is to eliminate residual carbon and oxygen impurities.

Furthermore, another recent challenge for realizing new function of cBN/diamond heterostructure will be also introduced.  

Biography of the Speaker:

   Education: -B.S., Tokyo University of Agriculture and Technology (1982)

-Ph.D., Tokyo Institute of Technology (1987) 

   Positions:　 Fellow of National Institute for Materials Science