标题： 压力诱导的反尖晶石结构Co$_2$TiO$_4$体积坍缩和金属化 显示英文标题

标题： Pressure-Induced Volume Collapse and Metallization in Inverse Spinel Co$_2$TiO$_4$

摘要： 逆尖晶石$Co_2TiO_4$ (CTO-Sp) 在高压 (HP) 条件下的结构、振动、电子和磁性性质通过X射线衍射、拉曼光谱、原位光学显微镜和第一性原理密度泛函理论 (DFT) 计算进行了系统研究。 在常压条件下，CTO-Sp 展现出空间群为$Fd\bar{3}m$的立方相，并在高压下经历两次显著的结构相变。 第一次相变发生在约7.3 GPa，导致四方面心-$I4_1/amd$相，单位晶胞体积变化最小。 {第二次转变发生在约17.3 GPa处，其中两种正交相在该压力以上出现并共存。}这第二次结构相变对应于一级相变，伴随着单位晶胞体积约17.5$\%$的显著减少。 CTO-Sp 及其高压后尖晶石相的体压缩率几乎等于每个相内的平均多面体压缩率。 DFT 计算揭示了高自旋到低自旋的转变，伴随着$Cmcm$正交相中局部磁矩的坍塌，导致样品的压力诱导金属化。 显示英文摘要

摘要： The structural, vibrational, electronic, and magnetic properties of inverse spinel $Co_2TiO_4$ (CTO-Sp) under high-pressure (HP) conditions are systematically investigated using X-ray diffraction, Raman spectroscopy, in situ optical microscopy, and first-principles density functional theory (DFT) calculations. At ambient conditions, CTO-Sp exhibits a cubic phase with a space group $Fd\bar{3}m$, and it undergoes two notable structural phase transitions at HP. The first transition, occurring at approximately 7.3 GPa, leads to the tetragonal-$I4_1/amd$ phase with minimal alteration in unit cell volume. {The second transition takes place near 17.3 GPa, where two orthorhombic phases emerge and coexist above this pressure.} This second structural transition corresponds to a first-order phase transition involving a significant reduction in unit cell volume of approximately 17.5$\%$. The bulk compressibility of CTO-Sp and its HP post-spinel phases is almost equal to the average polyhedral compressibility within each phase. DFT calculations reveal a high-spin to low-spin transition, accompanied by the collapse of local magnetic moments in the $Cmcm$ orthorhombic phase, leading to the sample's pressure-induced metallization.