Dimeric Molecular Structure of Molten Gallium Trichloride and a Hidden Evolution toward a Possible Liquid–Liquid Transition

Abstract

Group 13 trihalides MY 3 (M = Al, Ga, and In; Y = Cl, Br, and I) mostly having a dimeric M 2 Y 6 molecular structure in the solid state and a mixture of M 2 Y 6 dimers and MY 3 monomers in the vapor phase are potential candidates for entropy-driven liquid−liquid transition M 2 Y 6 ⇄ 2MY 3 at elevated temperatures. Using pulsed neutron diffraction and high-energy X-ray scattering supported by structural modeling, we show a dimer molecular structure of liquid GaCl 3 above the melting point at 351 K and midway between the boiling point (474 K) and the critical temperature (694 K) with almost hidden characteristic evolution toward a possible liquid−liquid transition. In contrast to edge-sharing (ES) dimers in solid and vapor of D 2h symmetry, the ES Ga 2 Cl 6 molecules in the melt have a puckered structure of the central four-membered ring with shorter Cl−Cl (2.90−3.09 Å) and longer Ga−Ga (3.20−3.26 Å) second-neighbor correlations. The elongation of Ga−Ga intramolecular distances with increasing temperature simultaneously with diminished Cl−Cl nearest neighbor contacts destabilizes the ES dimers, indicating the first step toward dimer dissociation.

Supercritical Gallium Trichloride in Oxidative Metal Recycling: Ga2Cl6 Dimers vs GaCl3 Monomers and Rheological Behavior

“…These distances were then converted into the Qspace. 25,32 They appear to be in excellent agreement with the experimental Q 0 (T), Figure 1d. The weak principal peak (PP1) at 2.1 Å −1 in S X (Q) decreases with increasing temperature and becomes nearly invisible above the critical point, Figure 1a.…”

“…The intermolecular distances 2 r WS were calculated using the Wigner-Seitz approach r WS = ( 3 / 4 π ) V m N A − 1 3 where V m is the molar volume and N A is the Avogadro constant. These distances were then converted into the Q -space. , They appear to be in excellent agreement with the experimental Q 0 ( T ), Figure d.…”

“…HE-XRD data for liquid gallium trichloride in Q -space: (a) structure factors S X ( Q ) at low Q and (b) interference functions Q [ S X ( Q ) – 1] over extended Q -range at 358 and 473 K, and 573, 653, and 723 K (this work); (c) density and (d) FSDP position Q 0 up to above the critical temperature at 694 K. Density, neutron and X-ray diffraction results from previous measurements are also shown. The estimated density of GaCl 3 along the liquid–vapor coexistence is shown in panel (c) as a pink dash-dotted line.…”

Glassy and liquid Sb2S3: insight into the structure and dynamics of a promising functional material

“…Further data analysis included absorption, Compton scattering, and polarization corrections using standard procedures 41 giving the total X-ray structure factor of S X (Q). 42,43…”

Transient Mesoscopic Immiscibility, Viscosity Anomaly, and High Internal Pressure at the Semiconductor–Metal Transition in Liquid Ga2Te3

“…Even a nonexhaustive search for structural evolution over the SC-M transition in liquid tellurides has shown that similar features (vanishing FSDP often shifting to higher Q) were observed in liquid Ge 0.15 Te 0.85 , 37−40 As 2 Te 3 , 41 supercooled tellurium, 23,42 Ga 2 Te 5 , and GeTe 2 (Figures S4 and S5). In contrast, a nearly invariant or slightly increasing FSDP moving in the opposite direction was reported for semiconducting liquid sulfides (As 2 S 3 , GeS 2 ), 22,43,44 selenides (P−Se, GeSe 2 ), 45−47 and chlorides (GaCl 3 ), 48 which were simply experiencing the thermal expansion without a concomitant density increase. Moreover, a presumable SC-M transition in liquid GeSe 2 above 1100 K was accompanied by a decreasing FSDP amplitude and a higher Q 0 shift, 49 which is a characteristic crossover from the typical lower-T semiconducting behavior.…”