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 M_nSi or MSi_n 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; 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 MnSi_1.7, 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 and trisilane. 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. Li_4.4Si is prepared from silicon and lithium metal in high-energy Ball mill process. One potential use is lithium battery electrodes.
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. 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 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 MnSi_1.73 was investigated as thermoelectric material and as an optoelectronic thin film. Single-crystal MnSi_1.73 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 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	d	FeSi₂, FeSi Xifengite\|, Fe₂Si, Fe₃Si
27	Cobalt	Co	9	4	d	CoSi, CoSi₂, Co₂Si, Co₂Si, Co₃Si
28	Nickel	Ni	10	4	d	Ni₃Si, Ni₃₁Si₁₂, Ni₂Si, Ni₃Si₂, NiSi, 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, YSi_1.4.
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
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, NdSi_x
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, 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	Si_1.8Yb,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, WSi₂
75	Rhenium	Re	7	6	d	Re₂Si, ReSi, ReSi_1.8 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 ThSi_2−x
91	Protactinium	Pa		7	f
92	Uranium	U		7	f	U₃Si, U₃Si₂, USi, U₃Si₅, USi_2−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