铁基Laves相合金的局域晶格结构与负热膨胀机理研究

As thermal expansion compensators, negative thermal expansion (NTE) materials have broad application prospects in the fields of microelectronics, aerospace, precision instruments, where high device thermal stability is demanded. The miniaturization and integration of devices has placed an urgent need for NTE materials with high thermal conductivity. Recently, Laves phase AFe2 alloy (A is a transition metal element) has attracted attention due to its adjustable NTE performance and good thermal conductivity. It is known that spin frustration, which reinforces the lattice contraction due to magnetic phase transition, is a key factor for the emergence of NTE. However, the micromechanism of NTE is not well understood yet. The average lattice information obtained by the usual diffraction method is difficult to give a reasonable explanation for the spin frustration and the microscopic magnetic effects, and is not able to accurately reflect the thermal expansion behavior of the local lattice as well. By employing the total scattering atomic pair distribution function which is a sensitive local lattice probe based on BL13W in Shanghai Synchrotron Radiation Facility, this project will study the local structure of AFe2 alloy and its temperature dependence; explain the physical origin of the microscopic magnetic effects from the perspective of local lattice; construct the mechanism at the atomic and nanoscale scales for the spin frustration tuned NTE. The proposed research will give references for optimizing and improving NTE performance in AFe2 alloys, and for designing new NTE materials having higher thermal conductivity as well.

作为热膨胀抑制剂，负热膨胀（NTE）材料在微电子、航空航天、精密仪器等对器件尺寸热稳定性要求苛刻的领域有着广阔应用前景。器件的微型化和集成化对高热导率NTE材料提出了迫切需求。最近，Laves相AFe2合金（A为过渡金属元素）因可调的NTE和良好导热性能而引起关注。已有的研究表明，自旋阻挫增强了磁相变诱发的晶格收缩效应，是导致NTE的重要因素，但对其微观机理还缺乏深入探讨。通常的衍射方法所得的平均晶格信息无法对自旋阻挫及相应微观磁效应给予全面的解释，也不能准确地反映局域晶格的热膨胀行为。本项目拟依托上海光源BL13W线站，采用全散射原子对分布函数这一灵敏的局域晶格探针，研究AFe2合金的局域晶格结构及其温度依赖关系；从局域晶格角度阐明微观磁效应的物理根源；在原子、纳米尺度上建立自旋阻挫调控NTE的物理图像，为优化和提高NTE性能提供依据；为设计新型高热导率NTE材料提供参考。

负热膨胀（NTE）材料在微电子、航空航天、精密仪器等对器件尺寸热稳定性要求苛刻的领域有着广阔应用前景。Laves相合金因具有可调的NTE和良好导热性能而引起关注。已有的研究表明，自旋阻挫增强了磁相变诱发的晶格收缩效应，是导致NTE的重要因素，但对其微观机理尚缺乏深入探讨。本项目执行过程中，我们以Laves相合金Hf0.87Ta0.13Fe2-xMx（M为Fe、Cu、Ni）为研究对象，利用同步辐射x射线原子对分布函数（PDF）和电子自旋共振（ESR）等研究手段，从自旋阻挫角度揭示了M原子占据Hf/Ta格点对微观磁性的影响机制，即这种占据引入了化学压力、局域磁扰动等，削弱了自旋阻挫，展宽了相变温窗（也即NTE温窗），而该过程未必与局域晶格畸变关联；以此为基础，引入过量M（Cu、Fe），Cu、Fe以单质形式析出，提高了Laves相合金的机械和热学性能，获得了综合性能优良的宽温区近/低膨胀新材料；揭示了Hf0.87Ta0.13Fe2中等静压导致的自旋阻挫增强效应和磁相变退耦合效应，获得了压力调制的宽温区磁热性能；本项目也探索了相变型NTE材料的新功能属性，如压致相变热效应、温敏热导率等。截至目前，在本项目资助下已发表论文12篇（Nature Communications和Acta Materialia各1篇），授权专利1项，在国内外学术会议上作交流报告3次，培养毕业研究生5名。我们的工作为优化和提高磁相变体系中NTE性能提供了参考依据，也为开发磁相变合金的新功能，扩大其应用领域提供了借鉴。