The nitridosilicates are chemical compounds that have anions with nitrogen bound to silicon. Counter cations that balance the electric charge are mostly electropositive metals from the alkali metals, alkaline earths or rare earth elements. Silicon and nitrogen have similar electronegativities, so the bond between them is covalent. Nitrogen atoms are arranged around a silicon atom in a tetrahedral arrangement.
Related compounds include pnictogenidosilicates :phosphidosilicates, arsenidosilicates and antimonosilicates; pnictogenidogernamates: phosphidogermanates. By replacing silicon, there are also nitridogermanates, nitridostannates, nitridotantalates and nitridotitanates.
Use Nitridosilicates are used as host substances for europium in LED phosphors. Examples include CASN (calcium aluminium silicide nitride) (CaAlSiN3), SCASN (SrCaAlSiN3) and SCSN (SrCaSiN3). These fluoresce red.
Production Nitridosilicates can be made in a solid state reaction by heating silicon nitride with metallic nitrides in a nitrogen atmosphere at over 1300 °C. If the mixtures are exposed to oxygen or air, then oxides or oxynitridosilicates are produced instead. Instead of metal nitrides, ammine complexes, amides or imides can be used instead. In place of the highly stable silicon nitride, silicon diimide can be used. Carbothermal reduction involves using a metal oxide or carbonate heated with carbon in a nitrogen atmosphere.
Properties The ratio of silicon to nitrogen varies from 1:4 to 7:10 (0.25 to 0.7) with increased condensation, and fewer sites for metals with high silicon content. At a ratio of 3:4 (0.75) there is no longer capacity for metal, as that is silicon nitride. The more condensed substances, with lower nitrogen content, have greater number of silicon atoms surrounding the nitrogen. This coordination number can vary from one to four, with the most common being three. The silicon atom always is coordinated by four nitrogen atoms. In the silicates, silicon is surrounded by four oxygen atoms, but each oxygen is only connected to one or two silicon atoms, and only very rarely three. So nitridosilicates can form more diverse structures than the silicates.
Nitridosilicates with higher proportion of silicon (more condensed) are more resistant to attack by water and oxygen, and so can be exposed to the atmosphere without decomposition. These condensed nitridosilicates are mechanically strong, and resistant to heat, acids and alkalis.
SiN4 tetrahedra can be connected to each other via vertices or edges. This differs from SiO4 which only connects via vertices.
Use Nitridosilicates have been used to make abrasives, turbine blades, cutting tools and phosphors.
Nitridosilicates nameformulaformula weightcrystal
systemspace
groupunit cellvolumedensitycommentsref LiSi2N3Li2SiN2Li5SiN3Li8SiN4Li18Si3N10Li21Si3N11I4a=9.4584 c=9.5194antifluorite structureBeSiN2 MgSiN2NaSi2N3 Ca2Si5N8332.64monoclinicCca = 14.3280 b = 5.61165 c = 9.69406 β = 112.1484 Z=4 721.92 3.06Eu orange fluorescence CaSiN2Ca3SiN3HmonoclinicC2/ca = 5.236 b = 10.461 c = 16.389 β = 91.182° Z = 8semiconductor: band gap 3.1 eV Ca4SiN4Ca5Si2N6Ca12Si4[SiN4]triclinicPa 9.0103 b 9.0218 c 13.8252 α 71.053° β 82.738° γ 69.763°blackCa16Si17N34CaMg3SiN4I41/aCa5[Si2Al2N8]orthorhombicPbcna = 9.255 b = 6.140 c = 15.578LiCa3Si2N5monoclinicC2/ca = 5.145 b = 20.380 c = 10.357 β = 91.24°Li4Ca3Si2N6288.24monoclinicC2/ma=5.787 b=9.705 c=5.977 β=90.45335.72.852Li2CaSi2N4Li2Ca2Mg2Si2N6Li2Ca3MgSi2N6CaMg3SiN4I41/aa = 11.424 c = 13.445 Z=16CaAlSiN3orthorhombicCmc21Eu yellow fluorescenceCaAlSi4N7orthorhombicPna21a = 11.6819, b = 21.0193, c = 4.9177 ÅCa4AlSiN5orthorhombicPna21a 11.2058 b 9.0512 c 6.0203faint redCa5Al2Si2N8orthorhombicPbcaa= 9.255 b = 6.140 c = 15.578 Z=4885.23.171yellow CaScSi4N7Manganese silicide dinitrideMnSiN2orthorhombic Pna21a = 5.271, b = 6.521, and c = 5.0706 V=174.26intense redFe2Si5N8364.23monoclinicCca= 14.0408 b = 5.32635 c = 9.5913 β = 110.728 Z=4decompose 1370K; brownZnSiN2 SrSiN2 Sr2Si5N8orthorhombicPmn21a = 5.71006 b = 6.81914 c = 9.33599 Z=2363.523.908Eu red fluorescenceSrSi6N8SrSi7N10Sr5Si7P2N16920.83Pnmaa=5.6748 b=28.0367 c=9.5280 Z=41522.14.018SrAlSi4N7orthorhombicPna21a = 11.742 b = 21.391 c = 4.966 Z = 81247.2Li2SrSi2N4cubica=10.69 Z=121220Li4Sr3Si2N6monoclinicC2/ma = 6.127, b = 9.687, c = 6.220, β = 90.24° Z=2369.13.876SrBeSi2N4p2ca=4.86082 c=9.42264 Z=2SrMg3SiN4I41/aa = 11.495 c = 13.512 Z=16Sr8Mg7Si9N22Cma 15.280 b 7.4691 c 10.936 β 110.462°SrAlSiN3Cmc21SrAlSi4N7Pna21 SrScSi4N7YScSi4N6ChexagonalP63mca=5.9109 c=9.677 CaYSi4N7 SrYSi4N7Ca8In2SiN4orthorhombicIbama = 12.904 b = 9.688 c = 10.899 Z = 4metallic BaSiN2Ba5Si2N6 Ba2Si5N8orthorhombicPmn21Eu red fluorescenceBaSi6N8Imm2a = 7.9316, b = 9.3437, c = 4.8357, Z = 2358.38BaSi7N10monoclinica = 6.8729, b = 6.7129, c = 9.6328, β = 106.269, Z = 2most condensedBa6Si6N10O2(CN2)Pa = 16.255, c = 5.469, Z = 3yellow, grown in liquid sodiumBaMg3SiN4Pa = 3.451 b = 6.069 c = 6.101 α = 85.200 β = 73.697 γ = 73.566° Z=1Ba2AlSi5N9triclinicP1a = 9.860 b = 10.320 c = 10.346 α = 90.37° β = 118.43° γ = 103.69° Z = 4Ba5Si11Al7N25Pnnma = 9.5923, b = 21.3991, c = 5.8889 Å Z = 2with Eu yellow emissionBaSi4Al3N9P21/Ca = 5.8465, b = 26.726, c = 5.8386 Å, β = 118.897° and Z = 4with Eu blue emission BaScSi4N7 BaYSi4N7 LaSi3N5orthorhombicP212121 a=7.853 b=11.264 c=4.8172 La3Si6N11tetragonalP4bmLa5Si3N9La7Si6N15Li5La5Si4N12tetragonalPb2a = 11.043 c = 5.573 Z = 2calcium lanthanum nitridosilicateCaLaSiN3Ca can be substituted by Yb or EuCaLaSi4N7CeSi3N5orthorhombicP212121Ce3Si6N11tetragonalP4bmCe3Si5N9Ce7Si6N15triclinicCe7Si6N15trigonalLi5Ce5Si4N12tetragonalPb2a = 10.978 c = 5.514 Z = 2PrSi3N5orthorhombicP212121Pr3Si6N11tetragonalP4bmPr5Si3N9Pr7Si6N15NdSi3N5orthorhombicP212121Nd3Si6N11tetragonalP4bmBa2Nd7Si11N23dark blueSm3Si6M11tetragonalP4bma=9.997 c=4.836Ca3Sm3[Si9N17]cubicP4_3ma=7.3950; Z=1404.4Eu2SiN3Cmcaa = 5.42, b = 10.610, c = 11.629, Z = 8dieuropium penta siliconoctanitrideEu2Si5N8orthorhombicPnm21a=5.7094 b=6.8207 c=9.3291 Z=2363.295.087redEuMg3SiN4I41/aa = 11.511 c = 13.552 Z=16Ca3Yb3[Si9N17]cubicP4_3ma=730.20 Z=1389.3BaYbSi4N7includes NSi4 clusterseuropium ytterbium tetrasiliconheptanitrideEuYbSi4N7hexagonalP63mca=5.9822 c=9.7455302.035.887brownSrYbSi4N7EuYbSi4N7 CaLuSi4N7 SrLuSi4N7 BaLuSi4N7Pb2Si5N8666.90orthorhombicPmn21a = 5.774 b = 6.837 c = 9.350269.116.001Pb-Pb dumbbells
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