Boride silicides (also called borosilicides) are mixed anion compounds containing silicide and boride linked into anions.
Synthesis Boride silicides may be produced by melting together the elements in a boron nitride crucible, sealed in tantalum. Tin may be used as a solvent. Alkali metal iodides can also be used as a solvent.
Use Borosilicides are of interest in research for ultra-high temperature materials for use in jet engines, catalysts and also for thermoelectric materials.
Structure There are not many different structures for borosilicides, particularly compared to the boride carbides. Most known compounds are rich in boron, but a few are rich in silicon. The boron and silicon atoms do not appear as isolated ions, but are covalently bound into a network. Boron networks found in metal borides are enlarged by the addition of silicon, which allows inclusion of metal atoms that are larger than would otherwise be stable.
Transition elements can form a tetragonal M5SiB2 series of compounds. These are called MAB phases (M for metal, A here is silicon, and B is boron). However the compounds for zirconium and hafnium are energetically unfavourable.
List formulasystemspace groupunit cell Å,volumedensitycommentrefα-SiB3rhombohedralband gap 0.2 eV; ignites 600 °Cβ-SiB3 (Si4B11.6C0.4)orthorhombicImmaa = 8.3915 b = 12.5680 c = 6.2134 Z = 16655.292.454transluscent and amber; Si4 chain and B12 cluster; band gap 2.0 eV; acid and base resistant; stands hot oxygenLiBSi2tetragonalP42/nmca=6.83225, c=8.83924 Z=8seven, six and five-membered rings; dark gray; moisture and acid stable; band gap 1.1 eVLi2B12Si2orthorhombicCmcea=6.1060 b=10.979 c=8.4050 Z=4transparent yellow; Vickers hardness=20.3 GPa; band gap 2.27 eVNa2B6Si2trigonalRma = 5.0735 c = 16.0004 Z=3356.3closo [B6]2− (Si2)0Na8B4.1Si41.9cubicI3ma=9.699 V=906.87Na8B74.5Si17.5hexagonalP63/mmca = 10.2392 c = 10.9215 Z=1991.622.480black; Na8(B12)6Si16[BSi]1.5[B2]0.5. B12MgB12Si2orthorhombicPnmaa=10.980 b=6.1098 c=8.3646 Z=4yellow-green; B12 icosahedra linked by SiMg3B36Si9CtrigonalRma=10.079 c=16.372black; acid stable; Vickers hardness 17.0 GPaNa3MgB37Si9trigonalRma = 10.1630 c = 16.5742 Z=31482.5K7B7Si39cubicPmna=9.952clathrateScB12.0C0.65Si0.071cubicF43ma=20.3085V5SiB2tetragonalI4/mcma=5.810 c=10.790CrSi3(B12)Se12(B2Se3)1.33hexagonalP6322a=12.9772 c=9.532 Z=21390.2blackMn5SiB2tetragonalI4/mcma=5.619 c=10.458330.17CrMn4SiB2tetragonalI4/mcma=5.6064 c=10.4244327.66.517ferromagnetic Curie T=270 KFe5SiB2tetragonalI4/mcma=5.555 c=10.342319.17Co4.75Si2BtetragonalI4/mcma=8.648 c=4.265318.9Ni6Si2BhexagonalP2ma=6.111 c=2.88493.252Rb8B8Si38cubicPmna = 9.9583 V=987.69 Z=13.0902air and water stable; semiconductor;YB17.6Si4.6rhombohedralR3ma=10.0841 c=16.4714YB41Si1.2orthorhombicPbama=16.674 b=17.667 c=9.5110Y1−xB12Si3.3−δ (0⩽x⩽0.5, δ≈0.3)rhombohedralRma=10.080 c=16.426 Z=9YB44Si2orthorhombicPbama=16.674 b=17.667 c=9.5112801.7Y2.04(B12)3(CSi)Si8trigonalRmY5Si2B8tetragonalP4/mbmZ=2Y2B36Si9CtrigonalRma=10.0344 c=16.348Nb5SiB2tetragonalI4/mcma=6.569 c=11.878 Z=4Superconductor Tc=7 K; for Nb5Si2.4B0.6 7.8KNb4VSiB2tetragonalI4/mcmNb4CrSiB2tetragonalI4/mcma = 6.109 c = 11.547Mo5SiB2tetragonalI4/mcma=6.0272 c=11.0671 Z=4oxidises to borosilicate; Superconductor Tc=5.6 KMo4VSiB2tetragonalI4/mcma= 5.9669 c= 11.02129Mo4MnSiB2tetragonalI4/mcma = 5.938 c = 11.057Ti4MoSiB2tetragonalI4/mcma= 6.13262 c= 11.52567band gap 4.1 eVMo4CrSiB2tetragonalI4/mcma = 5.939 c = 11.016Cs8B8Si38cubicPmna=10.0312 Z=11009.393.647formed under pressure; semiconductor; 3D network of dodecahedra and 14-hedra enclosing Cs ionsCeSi1·5B0.5hexagonalP6/mmma = 3.9922 c = 4.3053GdB18Si5tetragonalP4/mbma=7.2665 c=8.2229GdB44Si2Gd2B36Si9CtrigonalRma=10.0955 c=16.454Gd5Si2B8tetragonalP4/mbma=7.2665 c=8.2229metallicGd5Si3B0.6hexagonalP63/mcma=8.5080 c=6.4141Gd5Si23B8B6 octahedra and Si2Gd1−xB12Si3.3−δ (0⩽x⩽0.5, δ≈0.3)rhombohedralRma=10.069 c=16.447 Z=9Sm5Si2B8tetragonalP4/mbma=7.2616 c=8.2660 Z=2TbB41Si1.2orthorhombicPbamferromagnetic < 18 K; B12Si3 and B12 polyhedraTb9B3Si13.83R32a = 6.668 c = 12.405 Z=1Tb3-xC2Si8(B12)3Tb1−xB12Si3.3−δ (0⩽x⩽0.5, δ≈0.3)rhombohedralRma =10.075 b =10.075 c =16.41 Z=9TbB44Si2orthorhombicPbama=16.651 b=17.661 c=9.5002793.7Tb1.8C2Si8(B12)3rhombohedralRma=10.1171 c=16.397 Z=31453.4band gap 0.9 eVTb2B36Si9CtrigonalRma=10.0307 c=16.352Tb5Si2B8tetragonalP4/mbma=7.2616 c=8.2660 Z=2Dy0.7B12.33Si3trigonalRma=10.0782 c=16.4651 Z=91448.3blackDy1−xB12Si3.3−δ (0⩽x⩽0.5, δ≈0.3)rhombohedralRma=10.058 c=16.412 Z=9DyB44Si2orthorhombicPbama=16.658 b=17.655 c=9.508(2796.3Dy2B36Si9CtrigonalRma=10.0735 c=16.323Dy2.1(B12)3(CSi)Si8trigonalRmDy5Si2B8tetragonalP4/mbmZ=2Ho1−xB12Si3.3−δ (0⩽x⩽0.5, δ≈0.3)rhombohedralRma=10.062 c=16.365 Z=9HoB44Si2orthorhombicPbama=16.608 b=17.578 c=9.4922771.1Ho5Si2B8tetragonalP4/mbma=7.1830 c=8.9900 Z=2Ho2B36Si9CtrigonalRma=10.0643 c=16.2699Er1−xB12Si3.3−δ (0⩽x⩽0.5, δ≈0.3)rhombohedralRma=10.047 c=16.393 Z=9ErB44Si2orthorhombicPbama=16.600 b=17.621 c=9.485(5)2774.4Er2B36Si9CtrigonalRma=10.016 c=16.309Er3Si3.83 B (Er18Si23B6)trigonalR32a = 6.5568 c = 24.5541 Z = 6914.196.82shiny greyEr8B3Si17orthorhombicCmc21a=4.0128b=28.867 c=3.8413 Z=1Tm1−xB12Si3.3−δ (0⩽x⩽0.5, δ≈0.3)rhombohedralRma=10.068 c=16.350 Z=9TmB44Si2orthorhombicPbama=16.655 b=17.667 c=9.4942793.6Tm2B36Si9CtrigonalRma=10.0156 c=16.296Yb1−xB12Si3.3−δ (0⩽x⩽0.5, δ≈0.3)rhombohedralRma=10.095 c=16.470 Z=9YbB44Si2orthorhombicPbama=16.636 b=17.644 c=9.4882785.0YbB45.6Si1.0orthorhombica=16.636 b=17.644 c=9.488YbB3Si13.83R32a = 6.5796 c = 12.2599 Z=1Yb2B36Si9CtrigonalRma=10.1103 c=16.314Lu1−xB12Si3.3−δ (0⩽x⩽0.5, δ≈0.3)rhombohedralRma=10.062 c=16.297 Z=9Hf5Si3B0.2hexagonalP63/mcma = 7.8557 c = 5.52622 Z=2Ultra-high temperature ceramicW5SiB2tetragonalI4/mcmSuperconductor Tc = 5.8 KW4CrSiB2tetragonalI4/mcma = b: 5.942 c = 10.948W4.5Ta0.5SiB2tetragonalI4/mcmSuperconductor Tc=6.5 K
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