Ellipsometric study of electronic excitations in triglycine sulphate and triglycine selenate crystals

Abstract

AbstractThe real and imaginary parts of the pseudo‐dielectric susceptibility, 〈χ1〉(E) and 〈χ2〉(E), of triglycine sulphate (TGS) and triglycine selenate (TGSe) ferroelectric crystals have been obtained in the range 4–9.8 eV by spectroscopic ellipsometry using the Berlin Electron Storage Ring for synchrotron radiation source. A first maximum in 〈χ2〉(E) was found at E = 7.3 eV for both crystals and is attributed to the excitation of p‐electrons of oxygen. The spectra were measured at different temperatures in the range comprising the ferroelectric phase transition temperatures, 49 °C (TGS) and 22 °C (TGSe). Of note is the peak‐like behaviour in 〈χ1〉(T) and 〈χ2〉(T) near the phase transition temperature and a considerable decrease (about 50%) of the reflected light intensity IR in the range below the phase transition temperature (T < TC). The latter is probably caused by light scattering on the ferroelectric domain walls.