Broad-band dielectric spectroscopy of Ba2NaNb5O15 single crystal
Institute of Physics, ASCR, Na Slovance 2, 182 21 Prague 8, Czech Republic
Corresponding author: a firstname.lastname@example.org
Published online: 19 December 2002
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 Ti 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.
PACS: 63.20.-e – Phonons in crystal lattices / 64.70.Rh – Commensurate-incommensurate transitions / 77.80.Bh – Phase transitions and Curie point / 77.84.-s – Dielectric, piezoelectric, ferroelectric, and antiferroelectric materials
© EDP Sciences, Società Italiana di Fisica, Springer-Verlag, 2002