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Abstract
The sequence of phase transitions in barium sodium niobate was studied by means of infrared reflectivity measurements. Two kinds of samples, single crystal and thin films on platinum substrate, were investigated in the temperature interval 10–900 K. No phonon softening related to the ferroelectric phase transition at T1=830 K was observed. Strong dielectric anomaly near T1 is caused by soft dielectric relaxation below our spectral range. The observed softening of the B 2(y) mode explains the increase in the permittivity at low temperatures.