Sol-Gel-Process in the Ammono-System - a Novel Access to Silicon Based Nitrides

Abstract

Controlled coammonolysis of elementalkylamides in aprotic organic solvents at low temperatures have been shown to result in the formation of polyazanes. The synthetic procedure developed may be addressed as “sol‐gel‐route in the ammono system”. Pyrolysis of these novel polymer precursors gave access to multinary nitrides. For the model systems Si(NHMe)4/B(NMe2)3, Si(NHMe)4/Ti(NMe2)4, and Si(NHMe)4/Ta(NMe2)5 polymeric boro‐, titano and tantalosilazanes were obtained. Pyrolysis in ammonia at 1000 °C yielded amorphous silicon boron nitride, silicon titanium nitride and silicon tantalum nitride powders; further heating of the nitride powders at 1500 °C in nitrogen atmosphere led to the formation of partly crystalline composites of α‐Si3N4 and amorphous silicon boron nitride for the Si/B/N system, a composite of finely dispersed TiN and amorphous silicon titanium nitride for the Si/Ti/N system, and crystalline TaN and amorphous silicon nitride for the Si/Ta/N system. Furthermore, the structure and pyrolysis chemistry of the polymeric intermediates, as well as the morphology of the pyrolysis products, were studied by NMR, MAS‐NMR, FT‐IR, DTA‐TG‐MS, XRD, SEM, EDX and elemental analyses.

Solution Phase Preparative Routes to Nitride Morphologies of Interest in Catalysis

“…Transition metals have also been mixed into the silicon nitride framework at the precursor stage [34]. Ti(NMe 2 ) 4 , Ta(NMe 2 ) 5 , Zr(NMe 2 ) 4 were found to have similar ammonolysis rates to Si(NHMe) 4 and metal/silicon amide mixtures were exposed to ammonia.…”

Catalytic ammonolytic sol–gel preparation of a mesoporous silicon aluminium nitride from a single-source precursor

“…A number of sol-gel processes to prepare highly porous nonoxide ceramics have also been reported, e.g., boron nitride [4][5][6][7][8], metal (carbo)nitrides [9][10][11][12][13][14], silicon carbonitride [15][16][17][18][19][20][21] and boron carbonitride [22,23]. A sol-gel process in an ammono-system has been used to prepare polymeric boron-, titano-and tantalo-silazanes by controlled co-ammonolysis of the elemental alkylamides [24]. The preparation of B/C/N xerogels by a reaction of B-trichloroborazine with bis(trimethylsilyl)carbodimide has also been reported [25].…”

Nonoxide Sol–Gel Synthesis of Terbium‐Doped Silicon Nitride Phosphors

“…This approach has been used by Bradley and colleagues 18–20 using Si(NH 2 )(NMe 2 ) 3 and by Löffelholz et al 28 with Si(NHMe) 4 . A further variation is to use other nitrogen‐containing bridging groups such as (NCN) 2− , as used by Kroke and colleagues 18–20 to produce carbonitrides: …”

“…Si(NHMe) 4 leads to solid xerogels when a trifluoromethanesulfonic acid catalyst is used 26 and may be suitable for the production of phosphors similar to those described herein, but was not used here due to concern that Tb ions would not be immobilized in the oily products, and thus Tb‐rich regions could form. Previous studies by others 28 used a 1:1 or 1:2 ratio of boron or transition metal amide:Si(NHMe) 4 and these did lead to solid xerogels. It is likely that the second element (B or metal) underwent condensation reactions more readily resulting in a larger oligomer size, and therefore a solid product and that this does not occur with the very low doping levels used herein.…”

“…The use of such routes to incorporate other ions into silicon nitride, and hence modify its properties is also a general interest. Löffelholz et al 28 showed that B, Ti, or Ta could be doped into SiN x by adding the respective dimethylamide to the reaction between Si(NHMe) 4 and ammonia. These silicon nitride materials are referred to as SiN x rather than Si 3 N 4 because they are amorphous materials with a composition that deviates from Si 3 N 4 , similar to the vapor‐deposited SiN x films extensively used as capping layers and dielectrics in electronics.…”