Uniaxial Negative Thermal Expansion in an Orthorhombic Superconductor CoZr3

We investigated the temperature evolution of crystal structure of orthorhombic CoZr3, which is a superconductor with a transition temperature of 4.3 K, by synchrotron and laboratory (CuK{\alpha}) X-ray diffraction. Uniaxial negative thermal expansion along the c-axis, which is similar to that observed in tetragonal CoZr2, has been observed at a wide temperature range of T = 90-800 K in CoZr3, while a-and b-axis exhibit positive thermal expansion.