Non-hydrolytic sol–gel synthesis, properties, and high-pressure behavior of gallium molybdate

Abstract

A new material, Ga 2 Mo 3 O 12 , was prepared for the first time using non-hydrolytic sol-gel chemistry. Rietveld analysis of variable temperature X-ray diffraction data showed that this compound crystallizes in the monoclinic Sc 2 W 3 O 12 structure, and that it displays positive thermal expansion up to its decomposition temperature of 650 uC. No phase transitions were observed in this temperature range. The high-pressure behavior was investigated with an in situ synchrotron diffraction study. Reversible phase transitions to new monoclinic structures occurred at approximately 3.2 and 4.1 GPa. In addition, irreversible amorphization was observed above 8 GPa.

The Power of Non-Hydrolytic Sol-Gel Chemistry: A Review

“…Thus, it was shown, that Al-O-Ti system offers highly homogeneous products, which formed a metastable pseudo-brookite β-Al 2 TiO 5 phase during the calcination [59,60]. Similarly, many other systems were shown to produce highly homogeneous materials, as well as new and metastable phases (e.g., ZrTiO 4 [61], M 2 Mo 3 O 12 (M = Ga, Y, Sc, Fe, In, Al)) [62][63][64][65]. High homogeneity was described in the Al-O-Si [66] and Zr-O-Si [67] mixed oxides as well.…”

“…This thermodynamically unstable ternary oxide was obtained through the homogeneous mixing of Ga and Mo at the atomic level. The resulting solid decomposes to a mixture of Ga 2 O 3 and MoO 3 at 650 • C [65].…”

“…One of their research topics is the synthesis of crystalline ternary and quaternary metal oxides with A 2 M 3 O 12 stoichiometry (A = Al, Sc, Fe, In, Ga, Y, Mg-Zr, Mg-Hf, etc. ; M = Mo or W) that exhibit negative thermal expansion (NTE) [62][63][64][65]188,189]. The intrinsic advantage of NHSG chemistry-a high homogeneity of element mixing was fully exploited for NTE materials preparation.…”

Extremely Low Temperature Crystallization in the A2M3O12 Family of Negative Thermal Expansion Materials

“…To overcome this, the temperature of the solvothermal treatments was lowered to 80-100°C, as pure Ga 2 Mo 3 O 12 was previously reported to show an increasing tendency for formation of amorphous gallium oxides with increasing synthesis temperature between 110 and 150°C. [33] Surprisingly, samples reacted at these temperatures showed partial crystallization of the tars upon drying at 230°C, the lowest temperature at which a "raw powder" could be obtained. These powders recovered by drying the tars will be referred to as "raw" samples.…”

“…[22,[29][30][31][32] Several materials in the A 2 M 3 O 12 family have also been prepared by NHSG chemistry. This includes previously known stable compositions (A = Al, In, Sc, Y, Fe; M = Mo, W), as well as metastable Ga 2 Mo 3 O 12 , [33] which cannot be obtained by other routes at all, and new polymorphs like Pba2-Y 2 Mo 3 O 12 .…”