Uniaxial zero thermal expansion in low-cost Mn2OBO3 from 3.5 to 1250 K
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 $α$= -4(1)$\times$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.