The study investigates the thermal expansion and superconducting properties of a CuAl2‐type (tetragonal) superconductor CoZr2 under high pressures. High‐pressure synchrotron X‐ray diffraction is performed in a pressure range of 2.9 GPa < P < 10.4 GPa, and it is discovered that CoZr2 exhibits volumetric negative thermal expansion (NTE) under high pressures. Although uniaxial positive thermal expansion (PTE) along the a‐axis is observed under ambient pressure, it is suppressed by pressure, whereas a large uniaxial NTE along the c‐axis is maintained under the pressure regime. Because of the combination of the suppressed uniaxial PTE along the a‐axis and uniaxial NTE along the c‐axis, volumetric NTE is achieved under high pressure in CoZr2. The volumetric NTE mechanism is based on the flexible crystal structure caused by the soft Co–Co bond, as observed in the isostructural compound FeZr2, which exhibits a uniaxial NTE along the c‐axis. High‐pressure electrical resistance measurements of CoZr2 are performed and confirm superconductivity at 0.03 GPa < P < 41.9 GPa. Because of the coexistence of the two phenomena, volumetric NTE and superconductivity, in CoZr2 under high pressure, coexistence can be achieved under ambient pressure by tuning the chemical composition after the present observation.

中文翻译：

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CoZr2 超导体中压力引起的体积负热膨胀

该研究调查了 CuAl 的热膨胀和超导性能2‐型（四方）超导体 CoZr2在高压下。高压同步加速器X射线衍射在2.9 GPa <的压力范围内进行磷< 10.4 GPa，发现CoZr2在高压下表现出体积负热膨胀（NTE）。虽然沿单轴正热膨胀（PTE）A‐轴是在环境压力下观察到的，它受到压力的抑制，而沿着C‐轴保持在压力状态下。由于抑制单轴 PTE 沿A‐轴和单轴 NTE 沿C‐轴，在 CoZr 高压下实现体积 NTE2。体积 NTE 机制基于由软 Co-Co 键引起的柔性晶体结构，如在同构化合物 FeZr 中观察到的那样2，它沿着C-轴。CoZr的高压电阻测量2进行并确认超导性在 0.03 GPa <磷< 41.9 GPa。由于CoZr中同时存在体积NTE和超导两种现象2在高压下，通过在本次观察后调整化学成分，可以在环境压力下实现共存。