Pressure-induced volumetric negative thermal expansion in CoZr2 superconductor

Abstract

We investigate the thermal expansion and superconducting properties of a CuAl2-type (tetragonal) superconductor CoZr2 under high pressures. We perform high-pressure synchrotron X-ray diffraction in a pressure range of 2.9 GPa < P < 10.4 GPa and discover that CoZr2 exhibits volumetric negative thermal expansion under high pressures. Although the uniaxial positive thermal expansion (PTE) along the a-axis is observed under ambient pressure, that is suppressed by pressure, while the large uniaxial negative thermal expansion (NTE) along the c-axis is maintained under the pressure regime. As a result of a combination of the suppressed uniaxial PTE along the a-axis and uniaxial NTE along the c-axis, volumetric negative thermal expansion is achieved under high pressure in CoZr2. The mechanisms of volumetric NTE would be based on the flexible crystal structure caused by the soft Co-Co bond as seen in the iso-structural compound FeZr2, which exhibits uniaxial NTE along the c-axis. We also perform high-pressure electrical resistance measurements of CoZr2 to confirm the presence of superconductivity under the examined pressure regime in the range of 0.03 GPa < P < 41.9 GPa. We confirm the presence of superconductivity under all pressures and observe dome-like shape pressure dependence of superconducting transition temperature. Because of the coexistence of two phenomena, which are volumetric NTE and superconductivity, in CoZr2 under high pressure, the coexistence would be achievable under ambient pressure by tuning chemical compositions after our present observation.

22 pages, 7 figures, supporting information

References in corpus (8)

• Magnetic Ordering and Negative Thermal Expansion in PrFeAsO
• Superconducting and normal-state properties of the noncentrosymmetric superconductor Re6Zr
• Anomalous thermal expansion in a CuAl2-type superconductor CoZr2
• Sign change in c-axis thermal expansion and lattice collapse by Ni substitution in Co1-xNixZr2 superconductors
• Peak in the superconducting transition temperature of the nonmagnetic topological line-nodal material CaSb${}_2$ under pressure
• Axis thermal expansion switching in transition-metal zirconides TrZr2 by tuning the c/a ratio
• Uniaxial negative thermal expansion in an orthorhombic superconductor CoZr3
• Uniaxial negative thermal expansion in a tetragonal V3S-type superconductor IrZr3