Poster Presentation The 35th Biennial Conference of the Society of Crystallographers in Australia and New Zealand 2024 (Crystal 35)

Tunable low thermal expansion by atomic substitution in the Sc2-x-yFexAlYW3O12 family. (#118)

Liam J Mckinlay 1 , Neeraj Sharma 1
  1. School of Chemistry, UNSW, Sydney, NSW, Australia

Materials belonging to the ceramic family with the largest reported range of zero thermal expansion to date have been synthesised to formulate new zero thermal expansion materials and controllable thermal expansion.

Most materials expand when heated and contract when cooled but there are a small number of materials that contract upon heating, these are called negative thermal expansion (NTE) materials1. If the composition of these material is tightly controlled, a material that does not expand at all over a specified range can be synthesised forming zero thermal expansion (ZTE) materials. ZTE materials have a range of applications in precision engineering, most famously as mirror substrates for telescopes but also for use in micrometres and gauge blocks. Unfortunately the commercially available ZTE materials require arduous techniques to synthesise materials with ultra-low and zero thermal expansion and can struggle with uniformity and effective temperature ranges as they’re composite materials.

Investigations by the Sharma group revealed that a previously discovered ZTE material Sc1.5Al0.5W3O12 (Pnca) exhibited the largest reported range of ZTE to date with αV of -6(14) x10-8 K-1  from 4 to 1400 K2. The pressure properties of this material at room temperature were also recently investigated and found to be similar to other NTE ceramics with a low pressure <0.3 GPa phase change from orthorhombic to monoclinic and a soft bulk modulus of 17.4 GPa3. This material can be synthesised within 24 hours for small samples and is single phase. However it contains large amounts of scandium which is not found in large quantities globally, hence the material cost is significant. This work has developed new variants of this material by chemical substitution with inexpensive iron oxide, the new series of low thermal expansion materials yields coefficients of thermal expansion (CTE) in the range of αV = -4.24(6) and 2.80(8) x10-6 K-1 including near zero thermal expansion for the tested range of 300 to 1000 K. For comparison the CTE for metal like aluminium is αV of 69 x10-6 K-1 and fused quartz is 1.65 x10-6 K-1. These new materials have been modelled so that the desired CTE for selected application can be synthesised within the specified range. The materials have been analysed by a variety of techniques including variable temperature x-ray and neutron powder diffraction as well as ambient x-ray absorption spectroscopy.

 

  1. (1) Mary, T. A.; Evans, J. S. O.; Vogt, T.; Sleight, A. W. Negative Thermal Expansion from 0.3 to 1050 Kelvin in ZrW2O8. Science 1996, 272 (5258), 90-92. DOI: 10.1126/science.272.5258.90.
  2. (2) Liu, J.; Maynard-Casely, H. E.; Brand, H. E. A.; Sharma, N. Sc1.5Al0.5W3O12 Exhibits Zero Thermal Expansion between 4 and 1400 K. Chemistry of Materials 2021, 33 (10), 3823-3831. DOI: 10.1021/acs.chemmater.1c01007.
  3. (3) McKinlay, L. J.; Gerin, M.; Mittal, U.; Maynard-Casely, H. E.; Machon, D.; Radescu, S.; Sharma, N.; Pischedda, V. Pressure Behavior of the Zero Thermal Expansion Material Sc1.5Al0.5W3O12. Chemistry of Materials 2024. DOI: 10.1021/acs.chemmater.3c02126.