Tricritical Point Induced by Atomic Substitution in SbSexS1−xI

Abstract

Measurements of pyroelectric current in needle shaped crystals of SbSexS1−xI (x ⪅ 0.01, x = 0.30, 0.33, 0.34, 0.38, 0.40, 0.50, 0.65) are carried out by measuring the potential difference across a short circuiting resistance while heating the samples at uniform rates. These measurements, together with dielectric constant show that the critical temperature (Tc) follows a rapid linear decrease when x increases up to 0.65 with a slope of 33 K per 0.1 of Se concentration. The spontaneous polarization deduced from measurement of the pyroelectric current seems consistent with a mean field theory. It is found that a critical point, where the order of the transition changes from first to second, occurs at a value of x around 0.30 ± 0.03. The fact that the spontaneous polarization does not go to zero at the critical temperature but rather decreases gradually when the temperature increases, for T > Tc may be attributed to composition fluctuations and internal stresses.

Origin of soft mode in SbSexS1–xI crystals

“…As seen from Figs. (5,6,8,10) in the SbSe x S 1Àx I (x=0, 0.15, 0.45) crystals the IR soft mode observed and ferroelectric phase transition takes place. But in the SbSeI crystals nor IR soft mode nor the ferroelectric phase transition takes place.…”

“…They are influenced by light, leading to photoconductivity, photoferroelecticity, etc. Solid solutions of various combinations SbSISbSeI [6][7][8], SbSI-SbSBr [9,10], BiSI-SbSI [11][12][13] have been most intensively studied because they have the Curie temperatures depending on mixture composition. For example, the solid solutions SbSe x S 1-x I have the Curie temperature T C = 0-293 K, when x varies from 1 to 0.…”