Phase Diagram and Compositional Studies of Sc 2‐x‐y Fe x Al y W 3 O 12 : Discovery of New Zero and Low Thermal Expansion Materials

ABSTRACT This work reports on the discovery of new materials in the Sc 2‐x‐y Fe x Al y W 3 O 12 family. Members with compositions containing high concentrations of Fe are found to crystallize to a structure in the monoclinic P 2 1 / a symmetry, while compositions with low values of Fe and Al crystallize in the orthorhombic Pnca structure at room temperature. The orthorhombic samples in the compositional range x = 0.5, y ≤ 0.5 are found to transition to the monoclinic P 2 1 / a structure at 210–230 K. Specifically, Sc 1.25 Fe 0.5 Al 0.25 W 3 O 12 is found to exhibit a volumetric coefficient of thermal expansion (CTE) of −0.48(7) × 10 −6 K −1 over the range 300–1000 K, a near‐zero thermal expansion material—this CTE value is lower than precision invar variants and it is persistent over seven times the temperature range. Increasing the Al concentration to y = 0.75 increases the CTE to 4.69(8) × 10 −6 K −1 over the range 300–1000 K and decreasing it to y = 0 decreases the CTE to −4.22(6) × 10–6 K −1 over the range 300–1000 K. This work probes the phase‐space with an intention to correlate doping regimes to the physical property of volume change.