Nitridosilicate

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.^[1]

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.^[2]

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.^[3] Carbothermal reduction involves using a metal oxide or carbonate heated with carbon in a nitrogen atmosphere.^[4]

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.^[5] 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.^[6]

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.^[6] These condensed nitridosilicates are mechanically strong, and resistant to heat, acids and alkalis.^[1]

SiN₄ tetrahedra can be connected to each other via vertices or edges. This differs from SiO₄ which only connects via vertices.^[1]

Use

Nitridosilicates have been used to make abrasives, turbine blades, cutting tools and phosphors.^[4]

Nitridosilicates

name	formula	formula weight	crystal system	space group	unit cell	volume	density	comments	ref
	LiSi2N3								[5]
	Li2SiN2								[7]
	Li5SiN3								[7]
	Li8SiN4								[8]
	Li18Si3N10								[7]
	Li21Si3N11			I4	a=9.4584 c=9.5194			antifluorite structure	[7]
	BeSiN2								[9]
	MgSiN2								[5]
	NaSi2N3								[9]
	Ca2Si5N8	332.64	monoclinic	Cc	a = 14.3280 b = 5.61165 c = 9.69406 β = 112.1484 Z=4	721.92	3.06	Eu orange fluorescence	[5][10][4]
	CaSiN2								[5]
	Ca3SiN3H		monoclinic	C2/c	a = 5.236 b = 10.461 c = 16.389 β = 91.182° Z = 8			semiconductor: band gap 3.1 eV	[11]
	Ca4SiN4								[5]
	Ca5Si2N6								[5]
	Ca12Si4[SiN4]		triclinic	P1	a 9.0103 b 9.0218 c 13.8252 α 71.053° β 82.738° γ 69.763°			black	[12]
	Ca16Si17N34								[5]
	CaMg3SiN4			I41/a					[13]
	Ca5[Si2Al2N8]		orthorhombic	Pbcn	a = 9.255 b = 6.140 c = 15.578				[14]
	LiCa3Si2N5		monoclinic	C2/c	a = 5.145 b = 20.380 c = 10.357 β = 91.24°				[15]
	Li4Ca3Si2N6	288.24	monoclinic	C2/m	a=5.787 b=9.705 c=5.977 β=90.45	335.7	2.852		[5][16]
	Li2CaSi2N4								[5]
	Li2Ca2Mg2Si2N6								[5]
	Li2Ca3MgSi2N6								[5]
	CaMg3SiN4			I41/a	a = 11.424 c = 13.445 Z=16				[9]
	CaAlSiN3		orthorhombic	Cmc21				Eu yellow fluorescence	[17]
	CaAlSi4N7		orthorhombic	Pna21	a = 11.6819, b = 21.0193, c = 4.9177 Å				[18]
	Ca4AlSiN5		orthorhombic	Pna21	a 11.2058 b 9.0512 c 6.0203			faint red	[12]
	Ca5Al2Si2N8		orthorhombic	Pbca	a= 9.255 b = 6.140 c = 15.578 Z=4	885.2	3.171	yellow	[9][19]
	CaScSi4N7								[5]
Manganese silicide dinitride	MnSiN2		orthorhombic	Pna21	a = 5.271, b = 6.521, and c = 5.0706 V=174.26			intense red	[8]
	Fe2Si5N8	364.23	monoclinic	Cc	a= 14.0408 b = 5.32635 c = 9.5913 β = 110.728 Z=4			decompose 1370K; brown	[10]
	ZnSiN2								[9]
	SrSiN2								[5]
	Sr2Si5N8		orthorhombic	Pmn21	a = 5.71006 b = 6.81914 c = 9.33599 Z=2	363.52	3.908	Eu red fluorescence	[5][4][20]
	SrSi6N8								[5]
	SrSi7N10								[18]
	Sr5Si7P2N16	920.83		Pnma	a=5.6748 b=28.0367 c=9.5280 Z=4	1522.1	4.018		[21]
	SrAlSi4N7		orthorhombic	Pna21	a = 11.742 b = 21.391 c = 4.966 Z = 8	1247.2			[22]
	Li2SrSi2N4		cubic		a=10.69 Z=12	1220			[5][23]
	Li4Sr3Si2N6		monoclinic	C2/m	a = 6.127, b = 9.687, c = 6.220, β = 90.24° Z=2	369.1	3.876		[16]
	SrBeSi2N4			p62c	a=4.86082 c=9.42264 Z=2				[24]
	SrMg3SiN4			I41/a	a = 11.495 c = 13.512 Z=16				[9][13]
	Sr8Mg7Si9N22			Cm	a 15.280 b 7.4691 c 10.936 β 110.462°				[25]
	SrAlSiN3			Cmc21					[17]
	SrAlSi4N7			Pna21					[18]
	SrScSi4N7								[5]
	YScSi4N6C		hexagonal	P63mc	a=5.9109 c=9.677				[26]
	CaYSi4N7								[5]
	SrYSi4N7								[5]
	Ca8In2SiN4		orthorhombic	Ibam	a = 12.904 b = 9.688 c = 10.899 Z = 4			metallic	[11]
	BaSiN2								[5]
	Ba5Si2N6								[9]
	Ba2Si5N8		orthorhombic	Pmn21				Eu red fluorescence	[5][4]
	BaSi6N8			Imm2	a = 7.9316, b = 9.3437, c = 4.8357, Z = 2	358.38			[5][27]
	BaSi7N10		monoclinic		a = 6.8729, b = 6.7129, c = 9.6328, β = 106.269, Z = 2			most condensed	[5][28]
	Ba6Si6N10O2(CN2)			P6	a = 16.255, c = 5.469, Z = 3			yellow, grown in liquid sodium	[29]
	BaMg3SiN4			P1	a = 3.451 b = 6.069 c = 6.101 α = 85.200 β = 73.697 γ = 73.566° Z=1				[30]
	Ba2AlSi5N9		triclinic	P1	a = 9.860 b = 10.320 c = 10.346 α = 90.37° β = 118.43° γ = 103.69° Z = 4				[31]
	Ba5Si11Al7N25			Pnnm	a = 9.5923, b = 21.3991, c = 5.8889 Å Z = 2			with Eu yellow emission	[32]
	BaSi4Al3N9			P21/C	a = 5.8465, b = 26.726, c = 5.8386 Å, β = 118.897° and Z = 4			with Eu blue emission	[32]
	BaScSi4N7								[5]
	BaYSi4N7								[5]
	LaSi3N5								[5]
	La3Si6N11								[5]
	La5Si3N9								[9]
	La7Si6N15								[9]
	Li5La5Si4N12		tetragonal	P4b2	a = 11.043 c = 5.573 Z = 2				[33]
calcium lanthanum nitridosilicate	CaLaSiN3							Ca can be substituted by Yb or Eu	[34]
	CaLaSi4N7								[5]
	CeSi3N5								[9]
	Ce3Si6N11								[9]
	Ce3Si5N9								[9]
	Ce7Si6N15		triclinic						[9]
	Ce7Si6N15		trigonal						[9]
	Li5Ce5Si4N12		tetragonal	P4b2	a = 10.978 c = 5.514 Z = 2				[33]
	Pr3Si6N11								[9]
	Pr5Si3N9								[9]
	Pr7Si6N15								[9]
	Ba2Nd7Si11N23							dark blue	[35]
	Sm3Si6M11								[9]
	Ca3Sm3[Si9N17]		cubic	P4_3m	a=7.3950; Z=1	404.4			[36]
	Eu2SiN3			Cmca	a = 5.42, b = 10.610, c = 11.629, Z = 8				[9][37]
dieuropium penta siliconoctanitride	Eu2Si5N8		orthorhombic	Pnm21	a=5.7094 b=6.8207 c=9.3291 Z=2	363.29	5.087	red	[9][38]
	EuMg3SiN4			I41/a	a = 11.511 c = 13.552 Z=16				[13]
	Ca3Yb3[Si9N17]		cubic	P4_3m	a=730.20 Z=1	389.3			[36]
	BaYbSi4N7							includes NSi4 clusters	[9][39]
europium ytterbium tetrasiliconheptanitride	EuYbSi4N7		hexagonal	P63mc	a=5.9822 c=9.7455	302.03	5.887	brown	[9][38]
	SrYbSi4N7								[9]
	EuYbSi4N7								[9]
	CaLuSi4N7								[5]
	SrLuSi4N7								[5]
	BaLuSi4N7								[5]
	Pb2Si5N8	666.90	orthorhombic	Pmn21	a = 5.774 b = 6.837 c = 9.350	269.11	6.001	Pb-Pb dumbbells	[20]