Two-transition behavior in Bi0.5Sb0.5SeI crystals

Abstract The ions with outer electron configuration of ns2 are often considered key factors for the efficient carrier transport in optoelectronic materials. In many cases precise tuning of the band gap and adjustment of the desired electronic properties achieved through the changes of the chemical environment. Here we investigate BixSb1-xSeI (x = 0.5) mixed crystals that have a one-dimensional structure with intermediate physical parameters between BiSeI and SbSeI compounds. Although crystallographically the substitution appears to be trivial, we found, that it has a rather strong effect on chemical bonds that provoke two-mode Raman behavior as well as two electronic transitions. The temperature dependent electrical resistance and photoluminescence measurements indicated anomalies at ∼ 146 and ∼ 62 K with strong thermal hysteresis loop for Bi0.5Sb0.5SeI. These, mixed samples inherit anisotropic properties, but inhomogeneity prevail the structure. We assert that the difference in masses of bismuth and antimony should be responsible for the observed binary effect.