Neutron powder diffraction and high-pressure synchrotron x-ray diffraction study of tantalum nitrides

摘要

Tantalum nitride (TAN) compact with a Vickers hardness of 26 GPa is prepared by a high-pressure and high-temperature (HPHT) method.The crystal structure and atom occupations of WC-type TaN have been investigated by neutron powder diffraction,and the compressibility of WC-type TAN has been investigated by using in-situ high-pressure synchrotron x-ray diffraction.The third-order Birch-Murnaghan equation of state fitted to the x-ray diffraction pressurevolume (P-V) sets of data,collected up to 41 GPa,yields ambient pressure isothermal bulk moduli of B0 =369(2) GPa with pressure derivatives of B~ =4 for the WC-type TAN.The bulk modulus of WC-type TaN is not in good agreement with the previous result (B0 =351 GPa),which is close to the recent theoretical calculation result (B0 =378 GPa).An analysis of the experiment results shows that crystal structure of WC-type TaN can be viewed as alternate stacking of Ta and N layers along the c direction,and the covalent Ta-N bonds between Ta and N layers along the c axis in the crystal structure play an important role in the incompressibility and hardness of WC-type TaN.