Binary compounds of silicon


Binary compounds of silicon are binary chemical compounds containing silicon and one other chemical element. Technically the term silicide is reserved for any compounds containing silicon bonded to a more electropositive element. Binary silicon compounds can be grouped into several classes. Saltlike silicides are formed with the electropositive s-block metals. Covalent silicides and silicon compounds occur with hydrogen and the elements in groups 10 to 17.
Transition metals form metallic silicides, with the exceptions of silver, gold and the group 12 elements. The general composition is MnSi or MSin with n ranging from 1 to 6 and M standing for metal. Examples are M5Si, M3Si, M2Si, M3Si2, MSi and MSi2.
The Kopp–Neumann law applies as:
Cp = xCp + yCp
As a general rule, nonstochiometry implies instability. These intermetallics are in general resistant to hydrolysis, brittle, and melt at a lower temperature than the corresponding carbides or borides. They are electrical conductors. However, some, such as CrSi2, Mg2Si, β-FeSi2 and MnSi1.7, are semiconductors. Since degenerate semiconductors exhibit some metallic properties, such as luster and electrical conductivity which decreases with temperature, some silicides classified as metals may be semiconductors.

Group 1

Silicides of group 1 elements are saltlike silicides, except for silane whose bonds to hydrogen are covalent. Higher silane homologues are disilane and trisilane. Polysilicon hydride is a two-dimensional polymer network.
Many cluster compounds of lithium silicides are known, such as Li13Si4, Li22Si5, Li7Si3 and Li12Si7. Li4.4Si is prepared from silicon and lithium metal in high-energy Ball mill process. Potential uses include electrodes in lithium batteries. Li12Si7 has a Zintl phase with planar Si56− rings. Li NMR spectroscopy suggests these rings are aromatic.
Other group 1 elements also form clusters: sodium silicide can be represented by NaSi, NaSi2 and Na11Si36 and potassium silicide by K8Si46. Group 1 silicides are in general high melting, metallic grey, with moderate to poor electrical conductance and prepared by heating the elements. Superconducting properties have been reported for Ba8Si46. Several silicon Zintl ions are known with group 1 counter ions.

Group 2

Silicides of group 2 elements are also saltlike silicides except for beryllium whose phase diagram with silicon is a simple eutectic. Again there is variation in composition: magnesium silicide is represented by Mg2Si, calcium silicide can be represented by Ca2Si, CaSi, CaSi2, Ca5Si3 and by Ca14Si19, strontium silicide can be represented by Sr2Si, SrSi2 and Sr5Si3 and barium silicide can be represented by Ba2Si, BaSi2, Ba5Si3 and Ba3Si4. Mg2Si, and its solid solutions with Mg2Ge and Mg2Sn, are good thermoelectric materials and their figure of merit values are comparable with those of established materials.

Transition metals

The transition metals form a wide range of silicon intermetallics with at least one binary crystalline phase. Some exceptions exist. Gold forms a eutectic at 363 °C with 2.3% silicon by weight without mutual solubility in the solid state. Silver forms another eutectic at 835 °C with 11% silicon by weight, again with negligible mutual solid state solubility. In group 12 all elements form a eutectic close to the metal melting point without mutual solid-state solubility: zinc at 419 °C and > 99 atom percent zinc and cadmium at 320 °C.
Commercially relevant intermetallics are group 6 molybdenum disilicide, a commercial ceramic mostly used as an heating element. Tungsten disilicide is also a commercially available ceramic with uses in microelectronics. Platinum silicide is a semiconductor material. Ferrosilicon is an iron alloy that also contains some calcium and aluminium.
MnSi, known as brownleeite, can be found in outer space. Several Mn silicides form a Nowotny phase. Nanowires based on silicon and manganese can be synthesised from Mn5SiCl3 forming nanowires based on Mn19Si33. or grown on a silicon surface MnSi1.73 was investigated as thermoelectric material and as an optoelectronic thin film. Single-crystal MnSi1.73 can form from a tin-lead melt
In the frontiers of technological research, iron disilicide is becoming more and more relevant to optoelectronics, specially in its crystalline form β-FeSi2. They are used as thin films or as nanoparticles, obtained by means of epitaxial growth on a silicon substrate.
Atomic numberNameSymbolGroupPeriodBlockPhasesElement type
21ScandiumSc34dSc5Si3, ScSi, Sc2Si3, Sc5Si4Transition metal
22TitaniumTi44dTi5Si3, TiSi, TiSi2, TiSi3, Ti6Si4Transition metal
23VanadiumV54dV3Si, V5Si3, V6Si5, VSi2, V6Si5Transition metal
24ChromiumCr64dCr3Si, Cr5Si3, CrSi, CrSi2Transition metal
25ManganeseMn74dMnSi, Mn9Si2, Mn3Si, Mn5Si3, Mn11Si9Transition metal
26IronFe84dFe3Si, FeSi, FeSi2Transition metal
27CobaltCo94dCoSi, CoSi2, Co2Si, Co2Si, Co3SiTransition metal
28NickelNi104dNi3Si, Ni31Si12, Ni2Si, Ni3Si2, NiSi, NiSi2Transition metal
29CopperCu114dCu17Si3, Cu56Si11,Cu5Si, Cu33Si7, Cu4Si, Cu19Si6,Cu3Si,Cu87Si13Transition metal
30ZincZn124deutecticTransition metal
39YttriumY34dY5Si3, Y5Si4, YSi, Y3Si5, YSi1.4.Transition metal
40ZirconiumZr45dZr5Si3, Zr5Si4, ZrSi, ZrSi2, Zr3Si2, Zr2Si, Zr3SiTransition metal
41NiobiumNb55dNb5Si3, Nb4SiTransition metal
42MolybdenumMo65dMo3Si, Mo5Si3, MoSi2Transition metal
43TechnetiumTc75dTc4Si7 Transition metal
44RutheniumRu85dRu2Si, Ru4Si3, RuSi, Ru2Si3Transition metal
45RhodiumRh95dRhSi, Rh2Si, Rh5Si3, Rh3Si2, Rh20Si13Transition metal
46PalladiumPd105dPd5Si, Pd9Si2, Pd3Si, Pd2Si, PdSiTransition metal
47SilverAg115deutecticTransition metal
48CadmiumCd125deutecticTransition metal
57LanthanumLa36dLa5Si3, La3Si2, La5Si4, LaSi, LaSi2Lanthanide
58CeriumCe36fCe5Si3, Ce3Si2, Ce5Si4, CeSi, Ce3Si5, CeSi2Lanthanide
59PraseodymiumPr36fPr5Si3, Pr3Si2, Pr5Si4, PrSi, PrSi2Lanthanide
60NeodymiumNd36fNd5Si3, Nd5Si4, Nd5Si3,NdSi, Nd3Si4, Nd2Si3, NdSixLanthanide
61PromethiumPm36fLanthanide
62SamariumSm36fSm5Si4, Sm5Si3, SmSi, Sm3Si5, SmSi2Lanthanide
63EuropiumEu36fLanthanide
64GadoliniumGd36fGd5Si3, Gd5Si4, GdSi, GdSi2Lanthanide
65TerbiumTb36fSi2Tb, SiTb, Si4Tb5, Si3Tb5Lanthanide
66DysprosiumDy36fDy5Si5, DySi, DySi2Lanthanide
67HolmiumHo36fHo5Si3,Ho5Si4,HoSi,Ho4Si5,HoSi2Lanthanide
68ErbiumEr36fEr5Si3, Er5Si4, ErSi, ErSi2Lanthanide
69ThuliumTm36fLanthanide
70YtterbiumYb36fSi1.8Yb,Si5Yb3,Si4Yb3, SiYb, Si4Yb5, Si3Yb5Lanthanide
71LutetiumLu36fLu5Si3Lanthanide
72HafniumHf46dHf2Si, Hf3Si2, HfSi, Hf5Si4, HfSi2Transition metal
73TantalumTa56dTa9Si2, Ta3Si, Ta5Si3Transition metal
74TungstenW66dW5Si3, WSi2Transition metal
75RheniumRe76dRe2Si, ReSi, ReSi1.8 Re5Si3Transition metal
76OsmiumOs86dOsSi, Os2Si3, OsSi2Transition metal
77IridiumIr96dIrSi, Ir4Si5, Ir3Si4, Ir3Si5, IrSi3. Ir2Si3, Ir4Si7, IrSi2Transition metal
78PlatinumPt106dPt25Si7, Pt17Si8, Pt6Si5, Pt5Si2, Pt3Si, Pt2Si, PtSiTransition metal
79GoldAu116dEutectic diagram at linkTransition metal
80MercuryHg126deutecticTransition metal
89ActiniumAc37dActinide
90ThoriumTh37fTh3Si2, ThSi, Th3Si5, and ThSi2−xActinide
91ProtactiniumPa37fActinide
92UraniumU37fU3Si, U3Si2, USi, U3Si5, USi2−x, USi2 and USi3Actinide
93NeptuniumNp37fNpSi3, Np3Si2, and NpSiActinide
94PlutoniumPu37fPu5Si3, Pu3Si2, PuSi, Pu3Si5 and PuSi2Actinide
95AmericiumAm37fAmSi, AmSi2Actinide
96CuriumCm37fCmSi, Cm2Si3, CmSi2Actinide
97BerkeliumBk37fActinide
98CaliforniumCf37fActinide
99EinsteiniumEs37fActinide
100FermiumFm37fActinide
101MendeleviumMd37fActinide
102NobeliumNo37fActinide
103LawrenciumLr37fActinide

Group 13

In group 13 boron forms several binary crystalline silicon boride compounds: SiB3, SiB6, SiBn. With aluminium, a post-transition metal, a eutectic is formed with maximum solubility of silicon in solid aluminium of 1.5%. Commercially relevant aluminium alloys containing silicon have at least element added. Gallium, also a post-transition metal, forms a eutectic at 29 °C with 99.99% Ga without mutual solid-state solubility; indium and thallium behave similarly.

Group 14

is widely used as a ceramic or example in car brakes and bulletproof vests. It is also used in semiconductor electronics. It is manufactured from silicon dioxide and carbon in an Acheson furnace between 1600 and 2500 °C. There are 250 known crystalline forms with alpha silicon carbide the most common. Silicon itself is an important semiconductor material used in microchips. It is produced commercially from silica and carbon at 1900 °C and crystallizes in a diamond cubic crystal structure. Germanium silicide forms a solid solution and is again a commercially used semiconductor material. The tin–silicon phase diagram is a eutectic and the lead–silicon phase diagram shows a monotectic transition and a small eutectic transition but no solid solubility.

Group 15

is a ceramic with many commercial high-temperature applications such as engine parts. It can be synthesized from the elements at temperatures between 1300 and 1400 °C. Three different crystallographic forms exist. Other binary silicon nitrogen compounds have been proposed and other SiN compounds have been investigated at cryogenic temperatures. Silicon tetraazide is an unstable compound that easily detonates.
The phase diagram with phosphorus shows SiP and SiP2. A reported silicon phosphide is Si12P5, formed by annealing an amorphous Si-P alloy.
The arsenic–silicon phase diagram measured at 40 Bar has two phases: SiAs and SiAs2. The antimony–silicon system comprises a single eutectic close to the melting point of Sb. The bismuth system is a monotectic.

Group 16

In group 16 silicon dioxide is a very common compound that widely occurs as sand or quartz. SiO2 is tetrahedral with each silicon atom surrounded by 4 oxygen atoms. Numerous crystalline forms exist with the tetrahedra linked to form a polymeric chain. Examples are tridymite and cristobalite. A less common oxide is silicon monoxide that can be found in outer space. Unconfirmed reports exist for nonequilibrium Si2O, Si3O2, Si3O4, Si2O3 and Si3O5. Silicon sulfide is also a chain compound. Cyclic SiS2 has been reported to exist in the gas phase. The phase diagram of silicon with selenium has two phases: SiSe2 and SiSe. Tellurium silicide is a semiconductor with formula TeSi2 or Te2Si3.

Group 17

Binary silicon compounds in group 17 are stable compounds ranging from gaseous silicon fluoride to the liquids silicon chloride to the solid silicon iodide. The molecular geometry in these compounds is tetrahedral and the bonding mode covalent. Other known stable fluorides in this group are Si2F6, Si3F8 and polymeric solids known as polysilicon fluorides x and x. The other halides form similar binary silicon compounds.

The periodic table of the binary silicon compounds