Uniaxial zero thermal expansion in low-cost Mn2OBO3 from 3.5 to 1250 K

Abstract

Unique zero thermal expansion (ZTE) materials are valuable for use in precision instruments, including electronics, aerospace parts, and engines. However, most ZTE materials have a temperature range less than 1000 K under which they do not expand. In this study, we present a uniaxial ZTE in the low-cost Mn₂OBO₃ with a thermal expansion coefficient of −4(1) × 10⁻⁷ K⁻¹ along the X₁ principal axis from 3.5 to 1250 K. The monoclinic structure of Mn₂OBO₃ remains stable over the entire temperature range in ambient conditions. Considerable thermal contraction on the BO₃ trigonal planar and thermal expansion on the MnO₆ octahedra combine to produce uniaxial ZTE. Temperature-dependent Raman scattering reveals anharmonic low-frequency modes associated with MnO₆ Rigid Unit Modes (RUMs), which likely play a critical role in driving thermal contraction in the BO₃ trigonal planar. No charge order-disorder transition, which could cause thermal contraction, was observed up to 1250 K.