  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 $\alpha$=
-1.7$\times$10^(-7) K-1 along the [h00] direction 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. No charge order-disorder transition, which could cause thermal
contraction, was observed up to 1250 K.
