Synthesis Of Typical Transition Metal Nitrides Under High Pressure And High Temperature

The recent chemical synthesis of novel nitride compounds have aroused extensive studies due to their high hardness, corrosion resistance, mechanical stability.Moreover, the synthesis of transition-metal nitrides are regarded as a perfect way to search for potential superhard materials. There are tremendous potentials for discovering novel compounds of transition-metal nitride, cause introducing light elements such as carbon and nitrogen into interstitial sites in transition-metal(TM)lattice is anticipated to bring the high hardness. We have concentrated on the research of the tanalum nitrides and chromium nitrides. Although synthesis of transition-metal nitride compounds can be done by numbers of ways, high pressure is an irreplaceable method to synthesize new meterials with novel structures and properties. In the present work, three kinds of transition metal nitride compounds were synthesized using diamond anvil cell under high temperature and high pressure by three ways. The first one used elemental tantalum(99.9% purity) and molecular nitrogen for the raw materials, and the second was tantalum and sodium azide. The third is by employing chromium and sodium azide as reactant. In situ synchrotron X-ray diffraction experiment was used to analyze the possible crystal structure of the products.We present the synthesis of transition metal nitrides from three kinds of reactants in similar way. The first reactants were tantalum powder and molecular nitrogen. The tantalum powder was placed into a sample chamber, then liquid nitrogen was loaded into the sample chamber using COMPRES/GSECARS gas-loading equipment, which served as a reactant, thermal insulator and pressure transmitting medium. The sample was compressed to 16 GPa. The laser heating experiment was carried out using Nd :YLF laser, we gradually lifted the heating power to 18 W, and the temperature wasestimated to be about 1500 K. The second reactant tantalum and sodium azide were mixed in the ratio of 1 to 2, and the sample and ruby chips were placed into the sample chamber. Liquid argon was loaded into the sample chamber in glove box.Then the chamber was compressed to 21 GPa, and the laser power was increased to35 W in laser heating experiment. we estimated the temperature is up to 1500 K. In the third synthesis, reactants were chromium and sodium azide, which were mixed in the ratio of 1 to 1. The sample and ruby chips were placed into the sample chamber,then liquid neon was loaded into the chamber in glove box. The chamber was compressed to 30 GPa, and the laser heating experiment was performed to 18 W, the temperature was about 1500 K. The η-Ta2N3 was obtained from elemental tantalum and molecular nitrogen, the β-Ta2 N and mononitride θ-Ta N were synthesized from tantalum and sodium azide, the Cr N was obtained from chromium and sodium azide.This method ensures the samples were isolated from the ambient environment, air and water.