Infrared spectroscopy of Ba2NaNb5O15 single crystal and thin films

The sequence of phase transitions in barium sodium niobate was studied by m eans of infrared reflectivity measurements. Two kinds of samples, single cr ystal and thin films on platinum substrate, were investigated in the temper ature interval 10-900 K. No phonon softening related to the ferroelectric p hase transition at T-1=830 IC was observed. Strong dielectric anomaly near T-1 is caused by soft dielectric relaxation below our spectral range. The o bserved softening of the B-2(y) mode explains the increase in the permittiv ity at low temperatures.