  NEXCERA is a machinable and highly polishable ceramic with attractive
properties for use in precision instruments, in particular because its
coefficient of thermal expansion exhibits a zero crossing at room temperature.
We performed an accurate measurement of the long-term drift of the length of a
12~cm long NEXCERA block by using it as a spacer of a high-finesse optical
cavity. At room temperature, we found a fractional length drift rate
$L^{-1}d\Delta L/dt=-1.74\times10^{-8}~\mathrm{yr}^{-1}$.
