Yao Zhi-Yuan, Zhang Guo-Qin, Yao Wan-Wan, Wang Xiao-Zu, Qian Yin, Ren Xiao-Ming
State Key Laboratory of Materials-Oriented Chemical Engineering and College of Chemistry and Molecular Engineering, Nanjing Tech University, Nanjing 211816, P. R. China.
College of Chemical Engineering, Nanjing Tech University, Nanjing 211816, P. R. China.
Dalton Trans. 2020 Aug 4;49(30):10638-10644. doi: 10.1039/d0dt01833c.
The zero/negative thermal expansion (ZTE/NTE), which is an intriguing physical property of solids, has been observed in a few families of materials. ZTE materials possess practical applications in specific circumstances such as space-related applications, engineering structures and precision instrument. Generally, NTE materials are used as additives to form a composite of the ZTE material with positive thermal expansion material. It is still a tremendous challenge to design new families of ZTE/NTE materials. Herein, we presented a temperature-dependent single crystal structure analysis in 110-300 K for a layered (NH4)2V3O8, which crystallizes in a tetragonal space group P4bm and comprises mixed valence [V3O82-]∞ monolayers and NH4+ residual in the interlayer spaces. Along the c-axis, (NH4)2V3O8 demonstrated uniaxial expansion behaviors, i.e., ZTE with αc = -1.10 × 10-6 K-1 in 110-170 K and NTE with αc = -16.25 × 10-6 K-1 in 170-220 K. Along the a-axis, (NH4)2V3O8 exhibited ZTE with αa = + 2.06 × 10-6 K-1 in 240-300 K. The mechanisms of ZTE and NTE were explored using structural analysis. The conduction of NH4+ ions in the interlayer space was studied, indicating that the conductivity rapidly rises with the expansion of interlayer space at temperatures of >293 K. This study discloses that layered vanadates are promising ZTE/NTE materials.
零热膨胀/负热膨胀（ZTE/NTE）是固体中一种引人入胜的物理性质，已在少数几类材料中被观测到。ZTE材料在诸如空间相关应用、工程结构和精密仪器等特定情况下具有实际应用。一般来说，NTE材料用作添加剂，以形成ZTE材料与正热膨胀材料的复合材料。设计新的ZTE/NTE材料家族仍然是一个巨大的挑战。在此，我们展示了对层状(NH4)2V3O8在110 - 300 K温度范围内的单晶结构分析，该晶体属于四方空间群P4bm，由混合价态的[V3O82-]∞单层和层间空间中的NH4+残余物组成。沿着c轴，(NH4)2V3O8表现出单轴膨胀行为，即在110 - 170 K时αc = -1.10×10-6 K-1的ZTE以及在170 - 220 K时αc = -16.25×10-6 K-1的NTE。沿着a轴，(NH4)2V3O8在240 - 300 K时表现出αa = + 2.06×10-6 K-1的ZTE。利用结构分析探索了ZTE和NTE的机制。研究了层间空间中NH4+离子的传导，表明在温度>293 K时，电导率随着层间空间的扩大而迅速上升。这项研究表明层状钒酸盐是有前景的ZTE/NTE材料。
