  Recently, uniaxial negative thermal expansion (NTE) has been observed in
transition-metal zirconides including tetragonal (CuAl2-type) CoZr2 and
orthorhombic (Re3B-type) CoZr3. Here, we report the observation of uniaxial NTE
in tetragonal (V3S-type) IrZr3. With increasing temperature, the lattice
parameter for the a-axis and volume of IrZr3 increase, but the lattice
parameter for the c-axis decreases. IrZr3 is a superconductor with a transition
temperature of 2.3 K. The present result suggests that uniaxial NTE and related
anomalous axis thermal expansion occur in various transition-metal zirconides,
which will be important for designing superconducting device robust to
temperature cycles using zero-thermal-expansion superconductors.
