The thermal conductivities of three single crystals of BeO have been measured from 2 to 300 K. Phonons carry the heat at all temperatures. At 300 K the conductivity is 3.7 W/cm K, which is slightly less than that of copper. In the purest sample the maximum conductivity occurs at 45 K where it is 137 W/cm k, and at temperatures below 10 K the conductivity is limited by boundary scattering. The anisotropy in the conductivity of this hexagonal material is 20% or less.

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The crystal structure of fl-beryllia has been determined from X-ray powder data collected at 2100 °C The structure is tetragonal with a = 4.75 and c--2.74 A, and contains four molecules of BeO in the unit cell. The density is 2.69 g.cm -3. The structure is related to rutile, TiO~, in that the oxygen arrangement is identical. Beryllium atoms are in tetrahedral sites. The space group is P4~./mnm, and the oxygen and beryllium atoms are in sites 4(f) and 4(g) respectively with xo =0.310 and XBe --0"336.

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