Yttrium borides
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| Identifiers | |
|---|---|
| Properties | |
| YB6 | |
| Molar mass | 153.77 |
| Appearance | black powder |
| Density | 3.67 g/cm3 |
| Melting point | 2,300 °C (4,170 °F; 2,570 K) |
| Insoluble | |
| Structure | |
| cubic, cP7 | |
| Pm3m, No. 221 | |
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a = 0.41132 nm
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| Hazards | |
| Safety data sheet | External MSDS |
| NFPA 704 | |
| Flash point | Non-flammable |
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Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
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| Infobox references | |
Yttrium boride refers to a crystalline material composed of different proportions of yttrium and boron, such as YB2, YB4, YB6, YB12, YB25, YB50 and YB66. They are all gray-colored, hard solids having high melting temperatures. The most common form is the yttrium hexaboride YB6. It exhibits superconductivity at relatively high temperature of 8.4 K and, similar to LaB6, is an electron cathode. Another remarkable yttrium boride is YB66. It has a large lattice constant (2.344 nm), high thermal and mechanical stability, and therefore is used as a diffraction grating for low-energy synchrotron radiation (1–2 keV).
Yttrium diboride has the same hexagonal crystal structure as aluminium diboride and magnesium diboride – an important superconducting material. Its Pearson symbol is hP3, space group P6/mmm (No 191), a = 0.33041 nm, c = 0.38465 nm and the calculated density is 5.05 g/cm3. In this structure, the boron atoms form graphite like sheets with yttrium atoms between them. YB2 crystals are unstable to moderate heating in air – they start oxidizing at 400 °C and completely oxidize at 800 °C. YB2 melts at ~2100 °C.
YB4 has tetragonal crystal structure with space group P4/mbm (No. 127), Pearson symbol tP20, a = 0.711 nm, c = 0.4019 nm, calculated density 4.32 g/cm3. High-quality YB4 crystals of few centimeters in size can be grown by the multiple-pass floating zone technique.
YB6 is a black odorless powder having density of 3.67 g/cm3; it has the same cubic crystalline structure as other hexaborides (CaB6, LaB6, etc., see infobox). High-quality YB6 crystals of few centimeters in size can be grown by the multiple-pass floating zone technique. YB6 is a superconductor with the relatively high transition temperature (onset) of 8.4 K.
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