Negative thermal expansion (NTE) materials have been of continuous scientific and engineering. This behavior is exhibited by several families of oxides, one of which is the A2M3O12 family (A=trivalent cation, M=Mo, W).  These compounds show NTE in an orthorhombic structure, but some compositions transform to a monoclinic polymorph with positive expansion at low temperature. By tuning the metals incorporated into the structure, expansion and phase transition behavior can be easily modified. The potential phase transition to a monoclinic structure has adverse effects for potential applications, but can often be suppressed when the A-site is substituted by a mixture of cations.  The material of interest in this project is AlScMo3O12.  This compound was successfully synthesized using a non-hydrolytic sol gel route.  The goal was to determine reaction conditions that will give homogeneous AlScMo3O12 samples at low temperature. Improper choice of reaction variables may lead to phase separation into Al2Mo3O12 and Sc2Mo3O12.  Using high resolution synchrotron diffraction measurements, the homogeneity of samples could be confirmed, and Al:Sc ratios were estimated using  Rietveld refinement in combination with Vegard's law.  Samples that gave single phase material were confirmed to adopt the orthorhombic Sc2W3O12 structure as well as the desired 1:1:3 ratio for Al:Sc:Mo.  Conditions were optimized, creating a reproducible synthesis method with consistent stoichiometry and homogeneity characteristics of the AlScMo3O12 product.

Synthesis of homogeneous AlScMo<sub>3</sub>O<sub>12</sub>

247th National Meeting (2014)

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Synthesis of homogeneous AlScMo3O12

Synthesis of homogeneous AlScMo₃O₁₂