Determination of low-pressure crystalline–liquid phase boundary of SnI4

Abstract

The location of the liquidus in the low-pressure crystalline phase of SnI(4) was determined utilizing in situ x-ray diffraction measurements under pressures up to approximately 3.5 GPa. The liquidus is not well fitted to a monotonically increasing curve such as Simon's equation, but breaks near 1.5 GPa and then becomes almost flat. The results are compared to those from molecular dynamics simulations. Ways to improve the model potential adopted in the simulations are discussed.

Polyamorphism in tin tetraiodide

“…Our in situ x-ray experiments clarified that the melting curve of CP-I has a maximum. 16 More accurately, the melting curve is not a monotonically increasing curve but breaks near 1.5 GPa and then becomes almost flat 16 ͑the thick line in Fig. 1͒.…”

“…Moreover, the samples that melted below the break pressure could recover the Pa3 structure at ambient conditions, whereas those melted above that pressure could not. 16 This, plus the finding that the initial rapid increase in the melting point with pressure can be explained by the crystalline model consisting of rigid molecules interacting with van der Waals forces, 17 implies some qualitative change in the molecular form. 18 With this background, we conducted synchrotron x-ray diffraction measurements for the liquids just above their melting points, marked by the blue and pink circles in the pressure-temperature phase diagram shown in Fig.…”

“…Basically, the same sample assembly as described in Ref. 16 was adopted. However, to obtain clear-cut halos from the liquid sample, a diamond sleeve, instead of a BN sleeve, was sometimes used as a sample container.…”

On the pressure evolution of the melting temperature and the glass transition temperature

“…Reliable portraying of T g (P) and T m (P) evolutions is also significant for pressure-temperature equations of states, which make ultimate verifications of theoretical predictions possible [1-4, and references therein]. Since decades the Simon-Glatzel (SG) [18] equation is considered as the key tool for T m (P) parameterization [7,8,[19][20][21], namely: where T 0 m is the reference melting temperature, usually linked to atmospheric pressure, i.e.…”

Communication: Probable scenario of the liquid–liquid phase transition of SnI4

“…This value is consistent with the value derived from the initial slope of the melting curve. 18 Therefore, density measurements near the break point are highly desirable to justify the calculated results in Table I. 19 Finally, it is noted that our experimental findings do not necessarily deny the possibility that the LLCP is located below the melting curve, i.e., within the CP-I phase field.…”