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Optical properties of K 2 SeO 4 in the vicinity of phase transitions
Author(s) -
Pačesová S.,
Březina B.,
Jastrabík L.
Publication year - 1983
Publication title -
physica status solidi (b)
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.51
H-Index - 109
eISSN - 1521-3951
pISSN - 0370-1972
DOI - 10.1002/pssb.2221160226
Subject(s) - condensed matter physics , phonon , dielectric , phase transition , absorption edge , band gap , phase (matter) , atmospheric temperature range , photon energy , ion , ionic bonding , materials science , chemistry , photon , physics , optics , optoelectronics , organic chemistry , meteorology
Abstract The temperature dependence of the absorption edge of K 2 SeO 4 is measured in the range 300 to 4.2 K. In this temperature range the dependence of the absorption coefficient on the energy of photons and temperature is described by Urbach's rule. The magnitudes of the band gap obtained are E ∥ = 6.06 and E ⟂ = 6.14 eV for light polarized parallel and perpendicular to the a ‐axis. The temperature gradient of the band gap ( ∂E / ∂T )∥, ⟂ reveals a jump at the paraelectric‐incommensurate phase transition T 2 = 129.5 K for both polarizations of incident light in agreement with the second‐order nature of the phase transition. In the paraelectric phase, phonons with eigenfrequencies ω∥ = 218 cm −1 and ω⟂ = 181 cm −1 are interacting with the optical transitions. A switch‐over to the optical phonon of frequency ω∥,⟂ = 92 cm −1 is observed at T 2 together with the change of the electron‐optical‐phonon coupling constants indicating the increase of the ionic character of the bonds in the incommensurate phase between the K + ions and the (SeO 4 ) 2− tetrahedral groups.