Perturbation of fundamental band edge absorption of NaClO<inf>3</inf> crystals at high temperatures

The fundamental absorption band edge of NaClO3 crystal showed a shift towards longer wavelengths with increase in temperature. There is also evidence of formation of a new band at temperature higher than about 120°C. The shift is nearly linear up to about 120°C, but it is much larger than the linear rate as the melting point (≈ 250°C) is approached. The excess absorption is assumed to be due to the thermally produced lattice disorder and analysis yielded 1·40±0·05 eV for the energy of formation of the defect. The anomalous thermal expansion of the crystal reported by earlier workers at temperatures above 120°C could also be analysed in a similar manner and the activation energy of 1·45±0·05 eV so obtained is in reasonable agreement with that obtained from optical absorption studies. The additional absorption may be attributed to the perturbation of the fundamental absorption band due to defects formed at higher temperatures. © 1970.