Knowledge Bank

The infrared transmission spectra of thin single crystals of $KNiF3,KMgF3,KMnF3,KZnF3,KCOF3$ and $RbMnF3$ have been investigated from $1500cm-1$ to $20cm-1$ at $300\circ K$ and nitrogen temperatures. The spectra showed three broad absorptions corresponding to the three allowed infrared active optic modes in these cubic perovskite crystals. In the regions between these broad absorptions the samples transmitted from 50 per cent to 90 per cent of the incident energy when cooled to nitrogen temperatures. In these regions absorption bands have been observed which sharpen and shift to higher frequencies upon cooling to nitrogen temperatures. A fitting scheme is proposed to account for these absorptions as combinations of phonon modes from the edge of the Brillouin zone.