An infrared spectroscopic study of Li₂B₄O₇

The temperature evolution of the infrared powder spectra of lithium tetraborate Li₂B₄O₇ has been measured in the infrared region 50-1600 cm^-1 and over a temperature range between 20 K and 680 K. In contrast to the sharp B-O bands, the Li-related bands in the region between 300 cm^-1 and 510 cm^-1 are rather broad even at 20 K. With increasing temperature these bands show a stronger thermal response than in the higher-frequency region: the bands at 350 cm^-1 and 424 cm^-1 shift significantly in frequency and become very broad above 500 K. The 508 cm^-1 band appears to split into two individual bands near 500 K. The broadening of the Li-related bands is probably due to the thermally induced Li disorder. The temperature dependence of the B-O bending and stretching vibrations does not show clear evidence of structural phase transitions in Li₂B₄O₇ occurring in the temperature range between 20 K and 680 K.