Relationship between sintering methods and physical properties of the low positive thermal expansion material Al ₂ W ₃ O ₁₂

Abstract Ceramic materials from the A ₂ M ₃ O ₁₂ family with near‐zero thermal expansion are good candidates for applications requiring high thermal shock resistance. Considering their inherently low thermal conductivity, the bulk forms of A ₂ M ₃ O ₁₂ have to present Young's moduli and mechanical strength close to 100 GP a and 100 MP a, respectively, in order to compete with the state‐of‐the‐art materials used to avoid thermal shock. The relationship between sintering, microstructure, and physical properties within the A ₂ M ₃ O ₁₂ family is generally unknown while the preparation of bulks with high mechanical resistance remains a great challenge. Bulk samples of dense Al ₂ W ₃ O ₁₂ (96% TD ) have been obtained by pressureless three‐stage sintering ( TSS ) and spark plasma sintering ( SPS ). The Young's moduli and hardness of samples prepared by SPS were 50% higher than that measured for TSS samples and more than 100% in comparison to the Al ₂ W ₃ O ₁₂ bulk (91% TD ). UV ‐Vis spectroscopy confirmed that A ₂ M ₃ O ₁₂ phases are wide band‐gap semiconductors (3.11 eV ). When prepared by SPS , black Al ₂ W ₃ O ₁₂ absorbed light within the visible spectrum due to the introduction of donor sites within the band‐gap. No enhancement of the mechanism causing negative thermal expansion was observed for black Al ₂ W ₃ O ₁₂ . The mechanical properties achieved were significantly improved over those previously reported in literature for Al ₂ W ₃ O ₁₂ .