Pressure Behavior of the Zero Thermal Expansion Material Sc_1.5Al_0.5W₃O₁₂

Zero thermal expansion materials have a unique ability to withstand thermal shock over varied temperature ranges, enabling potential applications as components of high precision devices. The zero thermal expansion material Sc 1.5 Al 0.5 W 3 O 12 exhibits zero thermal expansion over the largest temperature range reported to date, from 4 to 1400 K (Liu et al. Chem. Mater. 2021, 33, 3823). In this work, the pressure stability of this material is investigated using high-pressure neutron and X-ray powder diffraction as well as Raman spectroscopy and supported with density functional theory (DFT) calculations. Sc 1.5 Al 0.5 W 3 O 12 shows an orthorhombic to monoclinic transition with the application of a small amount of pressure which is similar to that reported for other compositions in this family. Additional peak splitting is noted above 3.4 GPa which may indicate an additional phase transition. A pressure induced amorphization is found between 4.3 and 5.7 GPa and an amorphous to amorphous phase transition is further evidenced at around 15 GPa. The tungsten coordination sphere evolves from WO 4 to WO 6 as pressure is increased, which is evidenced by both DFT calculations and Raman spectroscopy. The <3.4 GPa monoclinic phase has a bulk modulus, B 0, of 17.4(14) GPa determined with X-ray powder diffraction by second order Birch–Murnaghan. This work demonstrates the importance of understanding structural changes under pressure for zero thermal expansion materials, as changes in pressure impart a more significant impact on the crystallographic volume compared to temperature.