We investigated the 300 K high-pressure behavior of ilmenite using Raman spectroscopy to 54 GPa. Upon compression, we observe a Fermi resonance between the lowest frequency A_g symmetry peaks (ν₄ and ν₅) between ~ 10 and ~ 30 GPa: bands that involve major components of Ti–O and Fe–O-related displacements, respectively. The peaks’ relative intensities switch at ~ 18 GPa and they also reach their minimum separation at ~ 20 GPa, indicating that their maximum resonance occurs between 18 and 20 GPa. The negative shift of the Ti–O-associated ν₄ vibration under compression is fully consistent with a shift in valence of Ti from 4 + to 3 + under compression. Anomalously small mode shifts of other, more localized vibrations are also consistent with a charge transfer from Fe to Ti under compression. At higher pressures, we have not found definitive evidence for a transition to the perovskite-structure at 300 K, which has been well characterized at high pressures and temperatures. At 40 GPa, we observe an apparent reversible disordering that persists up to our highest pressure. The 300 K mode shifts of the Raman active modes in FeTiO₃ under pressure are notably different from those of other ABO₃ compounds (where A = Mg, Mn and B = Ti, Si); in other ilmenite-structured compounds, the peaks shift at a faster rate and there has not been any observation of Fermi resonance. Thus, iron’s complex electronic structure, and its charge transfer with titanium, appears to play a primary role in the behavior of phonons in FeTiO₃ ilmenite.

我们使用拉曼光谱研究了钛铁矿在 54 GPa 下的 300 K 高压行为。在压缩时，我们观察到最低频率 A _g对称峰（ν ₄和 ν ₅）之间的费米共振，介于 ~ 10 和 ~ 30 GPa 之间：分别涉及 Ti-O 和 Fe-O 相关位移的主要成分的波段。峰的相对强度在 ~ 18 GPa 处切换，它们也在 ~ 20 GPa 处达到最小分离，表明它们的最大共振发生在 18 到 20 GPa 之间。Ti-O 相关 ν ₄的负移压缩下的振动与 Ti 的价态在压缩下从 4 + 到 3 + 的转变完全一致。其他更局部振动的异常小模式偏移也与压缩下从 Fe 到 Ti 的电荷转移一致。在更高的压力下，我们还没有发现在 300 K 时向钙钛矿结构转变的确切证据，这在高压和高温下已得到很好的表征。在 40 GPa 时，我们观察到一种明显的可逆无序，这种无序状态一直持续到我们的最高压力。FeTiO ₃在压力下的拉曼有源模式的 300 K 模式偏移与其他 ABO _{3 的}有明显不同化合物（其中 A = Mg、Mn 和 B = Ti、Si）；在其他钛铁矿结构的化合物中，峰以更快的速度移动，并且没有观察到任何费米共振。因此，铁的复杂电子结构及其与钛的电荷转移似乎在 FeTiO ₃钛铁矿中的声子行为中起主要作用。