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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.

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