Last weekend I attended a prelection at Polish Aviation Museum, on modern trends in aviation. The lecturer talked quite a bit of history too, and Soviet achievements were in as much focus as the western ones. Among all, he talked about missile guidance systems, including infrared homing.
He mentioned that materials for the superior (for its time) homing systems of air-to-air missiles were produced in a small furnace on board of Salyut, and later MIR space stations, as the manufacturing would be impossible in standard gravity; about 0.5kg of the material manufactured over a month of operation of the furnace would allow manufacturing of about 500 missiles with the superior guidance system.
Could someone provide more information - what substance exactly was being manufactured, and what about the process was so subtle that it required freefall conditions?