Sign change in c-axis thermal expansion and lattice collapse by Ni substitution in Co1-xNixZr2 superconductors

TL;DR

This study explores how Ni substitution in CoZr2 superconductors causes a sign change in c-axis thermal expansion and induces a lattice collapse, affecting superconductivity.

Contribution

It reveals the relationship between Ni content, thermal expansion behavior, and lattice collapse in Co1-xNixZr2 superconductors, highlighting a structural transition.

Findings

c-axis NTE observed for x<0.3

Lattice collapse occurs around x=0.6-0.8

Superconductivity is suppressed after lattice collapse

Abstract

We investigated the structural, electronic, and superconducting properties of Co1-xNixZr2, in which c-axis thermal expansion is systematically controlled. At x (smaller than) 0.3, c-axis negative thermal expansion (NTE) was observed, and the thermal expansion constant {\alpha}c approached zero with increasing x. At x = 0.4-0.6, zero thermal expansion was observed, and positive thermal expansion (PTE) appeared for x (greater than) 0.7. By analyzing the c/a ratio, we observed a possible collapsed transition in the tetragonal lattice at around x = 0.6-0.8. The lattice collapse results in c-axis PTE and the suppression of bulk superconductivity.