Low thermal expansion at cryogenic temperature in Fe39-xCo49+xCr10Ni2 alloy used for astronomical telescopes

Hiromichi T. Fujii; Naoki Sakaguchi; Kotaro Ona; Fumihiro Uraguchi; Yutaka Hayano; Toshihiko Yokoyama

doi:10.1117/12.2626196

29 August 2022 Low thermal expansion at cryogenic temperature in Fe_39-xCo_49+xCr₁₀Ni₂ alloy used for astronomical telescopes

Hiromichi T. Fujii, Naoki Sakaguchi, Kotaro Ona, Fumihiro Uraguchi, Yutaka Hayano, Toshihiko Yokoyama

Author Affiliations +

Proceedings Volume 12188, Advances in Optical and Mechanical Technologies for Telescopes and Instrumentation V; 1218806 (2022) https://doi.org/10.1117/12.2626196
Event: SPIE Astronomical Telescopes + Instrumentation, 2022, Montréal, Québec, Canada

Abstract

Fe₃₉Co₄₉Cr₁₀Ni₂ has exhibited ultra-low thermal expansion with its average coefficient of approximately 0.13 × 10⁻⁶/K between 100 K and 300 K from cryogenic to room temperatures. This value is extremely close to that of the fused silica used for cameras and spectrographs mounted on astronomical telescopes. The nature of the low thermal expansion of Fe_39−xCo₄₉+xCr₁₀Ni₂ has been clarified by the measurements of the magnetic properties and the numerical simulations based on the path-integral effective-classical-potential theory. The saturation magnetization is found to decrease with increasing temperature in the range from 100 K to 350 K. The rate of decrease becomes larger at temperatures over 150 K. The numerical calculation has shown that this magnetic behavior is attributed to the electronic state changes from high spin state to low spin state in the Co atoms, which occurs at temperatures over 150 K. The electronic state changes in Co atoms are found to strongly contribute to the low thermal expansion for the first time in Fe_39−xCo₄₉+xCr₁₀Ni₂.

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Hiromichi T. Fujii, Naoki Sakaguchi, Kotaro Ona, Fumihiro Uraguchi, Yutaka Hayano, and Toshihiko Yokoyama "Low thermal expansion at cryogenic temperature in Fe_39-xCo_49+xCr₁₀Ni₂ alloy used for astronomical telescopes", Proc. SPIE 12188, Advances in Optical and Mechanical Technologies for Telescopes and Instrumentation V, 1218806 (29 August 2022); https://doi.org/10.1117/12.2626196

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