High-Pressure Synthesis And Characterization For The Novel Nitrides Of Noble Metal-lrN_x And PtN_x

The designing of novel superhard materials with high strength, high hardness andheat-resistance performances，such as noble metal nitrides, is one of the front researchtopics in condensed matter physics at the present time. High-pressure synthesis for thenovel nitrides of noble metal (IrNxand PtNx) with high bulk modulus and uniqueelectronic structures, have absorbed many researchers’ interests during the pastdecades. Up to date, the noble metal nitrides have been synthesized by the laser-heating diamond-anvil-cell (LH-DAC) technique at extremily high pressureconditions (i.e.,45-50GPa,2000K) using the metal elements and N2as the rawmaterials.In this study, IrCl3, PtCl2and Li3N powders are used as raw materials,Large-volumn high pressure appratus are applied to synthesize the metal nitride viasolid-state reaction. IrNxand PtNxare obstained under relatively lower pressure (5～10GPa) and lower temperature (1273K).The crystal structures and chemicalcomposition of IrNxand PtNxwere studied in detail by first-principles calculationsand experimental measurements.Theoretical calculations and experimental researchresults revealed that the as-synthesized IrNxand PtNxcrystals all have a face-centeredcubic(fcc) crystal structure.The lattice constants of IrNxare4.07and the Ncontent(x) in IrNxis～0.3. The lattice constants of PtNxare changed from4.07to3.83.In order to study the synthesis mechanism of the noble metal nitrides, theexperimental conditions were changed, i.e., the molar radio of Ir:N, add NaCl asreaction inhibitor, increasing the synthesis pressure and temperature conditions,extending the reaction time, etc.. The results show that increasing molar radio of Pt:N,the lattice constants of PtNxchanged from4.07to3.83. More PtNxcrystals canbe synthesized by extending high pressure reaction time.