"Big K", the Platin-Iridium block in the French Museum Louvre in Paris defining the kg for around 130 years, had lost weight. A redefinition of the kg using fundamental constants was thus an urgent need.
For this purpose, the PTB (Physikalisch-Technische Bundesanstalt) pursued an approach of "counting" atoms in a silicon sphere.
Within the scope of the international Avogadro Project and national Kg projects, the IKZ Section Semiconductors developed (together with important Russian partners in Nischni Nowgorod) by the Float-Zone technique defect-free bulk crystals of highly enriched (up to 99.999 at%) silicon-28.
Only the IKZ with its expertise in crystal growth is able to achieve this precision in isotopically pure silicon crystal growth today.