For which solid is the speed of sound highest at 20°C?

Question

I am seeking the solid with the maximum possible speed of sound . At the begining I though it depended on the density of the solid but at the same temperature the element ruthenium give a higher speed for of sound than the denser element osmium. The difference is about $1000 \mathrm{m/s}$ at $20\mathrm{°C}$.

So can someone tell where and how can to find the solid in which the speed of the sound is the highest?

I emphasis that I am not asking only for the elements of the periodic table, it can be any solid material, even a mixture of materials.

Thank you in advance !

Answer 1

Light elements are best (all atoms are about the same size, low mass density and large Young's modulus make best speed).
Beryllium 12900 m/s, Boron 16,200m/s, diamond 18350 m/s, cubic BN 10300 m/s. Other solids, like LiH, LiBH4, B4C, hexagonal BN, and graphite, are worth checking, but I only find data for B4C(11000 m/s).

Diamond wins, but Beryllium is available in large chunks, and Boron in long filaments.