Binary compounds of silicon

Binary compounds of silicon are binary chemical compounds containing silicon and one other chemical element.Inorganic chemistry, Egon Wiberg, Nils Wiberg, Arnold Frederick Holleman 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 (Cu, V, Cr, Mo, Mn, Fe, Pt, U), M2Si (Zr, Hf, Ta, Ir, Ru, Rh, Co, Ni, Ce), M3Si2 (Hf, Th, U), MSi (Ti, Zr, Hf, Fe, Ce, Th, Pu) and MSi2 (Ti, V, Nb, Ta, Cr, Mo, W, Re).

The Kopp–Neumann law applies; heat capacities are linear in the proportion of silicon:

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. In general, they melt at high temperatures, appear metallic grey, conduct electricity moderately to poor, and are prepared by heating the elements. The major exception are the silanes, silicon-hydrogen compounds whose bonds are covalent. The parent, silane, is SiH4; higher homologues are disilane (Si2H6) and trisilane (Si3H8). Polysilicon hydride is a two-dimensional polymer network.

At the atomic level, group 1 silicides typically form cluster compounds. Several silicon phases include the Zintl ions (, , ). Li12Si7 has a Zintl phase with planar Si56− rings, and Li NMR spectroscopy suggests these rings are aromatic.

Lithium silicides include Li13Si4, Li22Si5, Li7Si3 and Li12Si7. Li4.4Si is prepared from silicon and lithium metal in high-energy Ball mill process. One potential use is lithium battery electrodes.Solid state ionics for batteries, Tsutomu Minami, Masahiro Tatsumisago

Sodium silicide can be represented by NaSi, NaSi2 and Na11Si36, and potassium silicide by K8Si46.

Group 2 Silicides of group 2 elements are also saltlike silicides except for beryllium whose phase diagram with silicon is a simple eutectic (1085 °C @ 60% by weight silicon). 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. Superconducting properties have been reported for Ba8Si46. 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 and inner 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 (18% atom percent) without mutual solubility in the solid state.Constitution of Binary Alloys, second edition, Max Hansen and Kurt Anderko, McGraw-Hill Book Co., (NY NY 1958) p. 232 and EG Heath, J. of Electro Control, 11, 1961, pp 13-15 as summarized in Constitution of Binary Alloys, First Supplement, Elliott, McGraw-Hill Book Inc., (NY NY 1965) p. 103 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 (< 99% Cd).

Commercially relevant intermetallics are group 6 molybdenum disilicide, a commercial ceramic mostly used as a 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 Mn(CO)5SiCl3 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.Wetzig, Klaus; Schneider, Claus Michael (eds.). Metal based thin films for electronics. Wiley-VCH, 2006 (2nd edition), p. 64. A silicon/iron-disilicide light-emitting diode operating at a wavelength of 1.5 μm. D. Leong, M. Harry, K. J. Reeson and K. P. Homewood. Nature 387, 686-688, 12 June 1997. They are used as thin films or as nanoparticles, obtained by means of epitaxial growth on a silicon substrate.

Atomic number Name Symbol Group Period Block Phases 21 Scandium Sc 3 4 d Sc5Si3, ScSi, Sc2Si3, 22 Titanium Ti 4 4 d Ti5Si3, TiSi, TiSi2, TiSi3, Ti6Si4 23 Vanadium V 5 4 d V3Si, V5Si3, V6Si5, VSi2, V6Si5 24 Chromium Cr 6 4 d Cr3Si, Cr5Si3, CrSi, CrSi2 25 Manganese Mn 7 4 d MnSi, Mn9Si2, Mn3Si, Mn5Si3, Mn11Si9 26 Iron Fe 8 4 dFeSi2, FeSi , Fe2Si, Fe3Si 27 Cobalt Co 9 4 d CoSi, CoSi2, Co2Si, Co2Si, Co3Si 28 Nickel Ni 10 4 d Ni3Si, Ni31Si12, Ni2Si, Ni3Si2, NiSi (Nickel monosilicide), NiSi2 29 Copper Cu 11 4 d Cu17Si3, Cu56Si11,Cu5Si, Cu33Si7, Cu4Si, Cu19Si6,Cu3Si,Cu87Si13 30 Zinc Zn 12 4 d eutectic 39 Yttrium Y 3 4 d Y5Si3, Y5Si4, YSi, Y3Si5, YSi1.4. 40 Zirconium Zr 4 5 d Zr5Si3, Zr5Si4, ZrSi, ZrSi2, Zr3Si2, Zr2Si, Zr3Si 41 Niobium Nb 5 5 d Nb5Si3, Nb4Si 42 Molybdenum Mo 6 5 d Mo3Si, Mo5Si3, MoSi2 43 Technetium Tc 7 5 d Tc4Si7 (proposed) 44 Ruthenium Ru 8 5 d Ru2Si, Ru4Si3, RuSi, Ru2Si3 45 Rhodium Rh 9 5 d RhSi, Rh2Si, Rh5Si3, Rh3Si2, Rh20Si13 46 Palladium Pd 10 5 d Pd5Si, Pd9Si2, Pd3Si, Pd2Si, PdSi 47 Silver Ag 11 5 d eutectic 48 Cadmium Cd 12 5 d eutectic 57 Lanthanum La 6 f La5Si3, La3Si2, La5Si4, LaSi, LaSi2 58 Cerium Ce 6 f Ce5Si3, Ce3Si2, Ce5Si4, CeSi, Ce3Si5, CeSi2 59 Praseodymium Pr 6 f Pr5Si3, Pr3Si2, Pr5Si4, PrSi, PrSi2 60 Neodymium Nd 6 f Nd5Si3, Nd5Si4, Nd5Si3,NdSi, Nd3Si4, Nd2Si3, NdSix 61 Promethium Pm 6 f 62 Samarium Sm 6 f Sm5Si4, Sm5Si3, SmSi, Sm3Si5, SmSi2 63 Europium Eu 6 f 64 Gadolinium Gd 6 f Gd5Si3, Gd5Si4, GdSi, GdSi2 65 Terbium Tb 6 f Si2Tb (terbium silicide), SiTb, Si4Tb5, Si3Tb5 66 Dysprosium Dy 6 f Dy5Si5, DySi, DySi2 67 Holmium Ho 6 f Ho5Si3,Ho5Si4,HoSi,Ho4Si5,HoSi2 68 Erbium Er 6 f Er5Si3, Er5Si4, ErSi, ErSi2 69 Thulium Tm 6 f 70 Ytterbium Yb 6 f Si1.8Yb,Si5Yb3,Si4Yb3, SiYb, Si4Yb5, Si3Yb5 71 Lutetium Lu 3 6 d Lu5Si3 72 Hafnium Hf 4 6 d Hf2Si, Hf3Si2, HfSi, Hf5Si4, HfSi2 73 Tantalum Ta 5 6 d Ta9Si2, Ta3Si, Ta5Si3 74 Tungsten W 6 6 d W5Si3, WSi2Tungsten: Properties, Chemistry, Technology of the Element, Alloys, and Chemical Compounds Lassner, Erik, Schubert, Wolf-Dieter 1999 75 Rhenium Re 7 6 d Re2Si, ReSi, ReSi1.8 Re5Si3 76 Osmium Os 8 6 d OsSi, Os2Si3, OsSi2 77 Iridium Ir 9 6 d IrSi, Ir4Si5, Ir3Si4, Ir3Si5, IrSi3. Ir2Si3, Ir4Si7, IrSi2 78 Platinum Pt 10 6 d Pt25Si7, Pt17Si8, Pt6Si5, Pt5Si2, Pt3Si, Pt2Si, PtSi 79 Gold Au 11 6 d Eutectic diagram at link 80 Mercury Hg 12 6 d eutectic 89 Actinium Ac 7 f 90 Thorium Th 7 f Th3Si2, ThSi, Th3Si5, and ThSi2−xas summarized in Constitution of Binary Alloys, Second Supplement, Francis A. Shunk, McGraw-Hill Book Inc., (NY NY 1969) p. 681-82. 91 Protactinium Pa 7 f 92 Uranium U 7 f U3Si, U3Si2, USi, U3Si5, USi2−x, USi2 and USi3 93 Neptunium Np 7 f NpSi3, Np3Si2, and NpSi 94 Plutonium Pu 7 f Pu5Si3, Pu3Si2, PuSi, Pu3Si5 and PuSi2 95 Americium Am 7 f AmSi, AmSi2 96 Curium Cm 7 f CmSi, Cm2Si3, CmSi2 97 Berkelium Bk 7 f 98 Californium Cf 7 f 99 Einsteinium Es 7 f 100 Fermium Fm 7 f 101 Mendelevium Md 7 f 102 Nobelium No 7 f 103 Lawrencium Lr 3 7 d 104 Rutherfordium Rf 4 7 d 105 Dubnium Db 5 7 d 106 Seaborgium Sg 6 7 d 107 Bohrium Bh 7 7 d 108 Hassium Hs 8 7 d 109 Meitnerium Mt 9 7 d 110 Darmstadtium Ds 10 7 d 111 Roentgenium Rg 11 7 d 112 Copernicium Cn 12 7 d

Group 13 In group 13 boron (a metalloid) forms several binary crystalline silicon boride compounds: SiB3, SiB6, SiBn. With aluminium, a post-transition metal, a eutectic is formed (577 °C @ 12.2 atom % Al) 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 Silicon carbide (SiC) 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 Silicon nitride (Si3N4) 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 (SiN, Si2N3, Si3N) and other SiN compounds have been investigated at cryogenic temperatures (SiN2, Si(N2)2, SiNNSi). Silicon tetraazide is an unstable compound that easily detonates.

The phase diagram with phosphorus shows SiP and SiP2. A reported silicon phosphide is Si12P5 (no practical applications), 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