Low and increased solubility of silicon in metal nitrides: evidence by X-ray absorption near edge structure (original) (raw)
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Interface Structure and Atomic Bonding Characteristics in Silicon Nitride Ceramics
Science, 2004
Direct atomic resolution images have been obtained that illustrate how a range of rare-earth atoms bond to the interface between the intergranular phase and the matrix grains in an advanced silicon nitride ceramic. It has been found that each rare-earth atom bonds to the interface at a different location, depending on atom size, electronic configuration, and the presence of oxygen at the interface. This is the key factor to understanding the origin of the mechanical properties in these ceramics and will enable precise tailoring in the future to critically improve the materials' performance in wide-ranging applications.
Interfacial structure in silicon nitride sintered with lanthanide oxide
Journal of Materials Science, 2006
Three independent research groups present a comparison of their structural analyses of prismatic interfaces in silicon nitride densified with the aid of lanthanide oxide Ln2O3. All three groups obtained scanning transmission electron microscope images which clearly reveal the presence of well-defined Ln segregation sites at the interfaces, and, moreover, reveal that these segregation sites are element-specific. While some results differ across the three research groups, the vast majority exhibits good reproducibility.
The Structure of Grain Boundaries in Silicon Nitride Based Alloys
Processing of Crystalline Ceramics, 1978
Grain boundaries in silicon-based ceramics have been characterized by high resolution electron microscopy including the technique of lattice fringe imaging~ and this work is illustrated with examples from b~th h~t-pressed sil~con nitrides (MgO and Y203 fluxed) and a magnes~~-s~alon (Mg 1 8~~1.Br4l2.4?03.l9~3 8l)' .Roo~ tem~erature observat~ons of the glassy pnase are cons~stent w~th ~t be~ng only a partially wetting phase~ indicating that it cannot form a continuous film. The atomic configuration of the grain boundaries in both materials is presented together with lattice fringe observations of segregation at grain boundaries in the magnesium-sialon. H. Palmour III et al. (eds.
MICROSTRUCTURE OF Si 3 N 4 FILMS DEPOSITED ON VARIOUS SUBSTRATES BY CVD
Le Journal de Physique Colloques, 1986
Resume -Nous avons prepare des bicouches afin d16tudier les relations qui GZG'Ent entre les proprietCs mecaniques et la microstructure de composites Sic-Si3N4. Des couches de Si 3N4, obtenues ? I basse pression, par decomposition de Si(CH3)4 dans une chambre isotherme a 1300°C, ont ete deposees sur du Sic monocristallin ou fritte. Nous avons determine leurs structures cristallines par diffraction des rayons X. L1influence du substrat sur leur microstructure a &t& etudiee par microscopie electronique ?I balayage ou a transmission.
The formation and role of interfaces in superhard nc-MenN/a-Si3N4 nanocomposites
2007
The early finding of Veprek and Reiprich that the maximum hardness in the nc-TiN/Si 3 N 4 nanocomposites is achieved at about one monolayer of the interfacial Si 3 N 4 has been confirmed for a number of different nc-Me n N/X x N m systems (Me = Ti, W, V, (TiAl)N,…; X = Si, B). More recently, this has been confirmed experimentally for TiN-Si 3 N 4 heterostructures and by first principle density functional theory calculations. We present a consistent understanding of the formation of the nanocomposites with one monolayer Si 3 N 4 interface by spinodal phase segregation. This interface is energetically stabilized as compared to bulk Si 3 N 4 , which results in an enhanced bond strength and corresponding cohesion energy. Such an enhancement appears to be of a general validity in nano-sized solids with well-ordered interfaces. The paper concludes a brief summary of the recent progress of the understanding of the mechanical properties of these nanocomposites.
Surface Structure of Commercial Si3N4 Powders Analyzed by X-Ray Photoelectron Spectroscopy (XPS)
Journal of the Ceramic Society of Japan, 2005
Surface structures of seven different commercial Si 3 N 4 powders were investigated by X-ray photoelectron spectroscopy XPS. The evaluated powders were produced by three different methods: diimide precipitation, carbothermal reduction and nitridation of silicon using different nitriding media with final treatments. The XPS spectra of all as received powders show Si2p, C1s, N1s and O1s signals after 0, 5 and 10 s etching priods. Tetrahedral structures Si-XYZW with different atoms Si; H; N; O or groups NH; NH 2 ; OH in XYZ and W, from here after substituted by them, were observed for all as received commercial Si 3 N 4 powders. For five out of the seven Si 3 N 4 powders, the two main tetrahedra present on the most outer surface layer are Si-SiSiN OH , and tetrahedra containing O; Si-O NNN; SiSiH; SiNN; NNO. The two powders produced by nitridation of silicon with HF acid washing in the final treatment present Si-SiSiN NH 2 and tetrahedra containing OH; Si-SiN Si; N OH. The powder produced by carbothermal reduction process using NH 3 g presents the highest fraction of O containing tetrahedra. For all powders after 5 and 10 s etching periods, the main structure changed to NH 2 ; Si-SiN H; Si NH 2 and NH groups containing configurations Si-SiN Si; N NH , respectively. The surface of Si 3 N 4 powders of any production method does not have structure close to SiO 2 , Si 2 N 2 O or an intermediate between them as commonly accepted.
Surface and Coatings Technology, 2005
Ti 1Àx Si x N (0 x 0.14) thin solid films were deposited onto cemented carbide (WC-Co) substrates by arc evaporation. X-ray diffraction and transmission electron microscopy showed that all films were of NaCl-structure type phase. The as-deposited films exhibited a competitive columnar growth mode where the structure transits to a feather-like nanostructure with increasing Si content. Films with 0 x 0.01 had a b111À crystallographic preferred orientation which changed to an exclusive b200À texture for 0.05 x 0.14. X-ray photoelectron spectroscopy revealed the presence of SiN bonding, but no amorphous Si 3 N 4. Band structure calculations performed using a full potential linear muffin tin orbital method showed that for a given NaCl-structure Ti 1Àx Si x N solid solution, a phase separation into cubic SiN and TiN is energetically favorable. The microstructure was maintained for the Ti 0.86 Si 0.14 N film annealed at 900-C, while recrystallization in the cubic state took place at 1100-C annealing during 2 h. The Si content influenced the film hardness close to linearly, by combination of solid-solution hardening in the cubic state and defect hardening. For x = 0 and x = 0.14, nanoindentation gave a hardness of 31.3 T 1.3 GPa and 44.7 T 1.9 GPa, respectively. The hardness was retained after annealing at 900-C, while it decreased to below 30 GPa for 1100-C following recrystallization and W and Co interdiffusion.