Eur. Phys. J. B 30, 319-329 (2002)
https://doi.org/10.1140/epjb/e2002-00385-4

Broad-band dielectric spectroscopy of Ba₂NaNb₅O₁₅ single crystal

Institute of Physics, ASCR, Na Slovance 2, 182 21 Prague 8, Czech Republic

Corresponding author: ^a buixader@fzu.cz

Received: 24 August 2002
Published online: 19 December 2002

Abstract

Barium sodium niobate (BNN) single crystals are studied by IR spectroscopy, time-domain THz transmission spectroscopy, HF coaxial wave-guide technique and LF dielectric spectroscopy to cover the frequency range 10²–10¹⁴ Hz in a wide temperature interval. The dielectric response parallel and perpendicular to the polar c-axis is discussed. The ferroelectric transition at  K is driven by a relaxational soft mode coupled with another central-mode type relaxation which both gradually disappear on cooling in the ferroelectric phase. Below T_i the parameters of the expected IR active amplitudon were estimated. The low-temperature permittivity increase on cooling for the field direction has been explained by an incipient proper ferroelectric-ferroelastic transition driven by an IR and Raman active B₂-symmetry soft mode.