Mineral pressure gauge based on lattice stability and plasmonic enhancement of cobalt titanate under high pressure

Titanium cobalt oxide $\mathrm{CoTi}{\mathrm{O}}_{3}$ (CTO) with ilmenite structure has attracted considerable attention in functional materials owing to their multiferroic and chemical stability characteristics similar to $\mathrm{FeTi}{\mathrm{O}}_{3}$ and perovskites. However, information about structural stability and lattice deformation of CTO under high pressure remains unclear. Here, we present a unique pressure gauge through a quantitative investigation on the vibrational properties of compressed CTO by in situ high-pressure Raman experiments up to 40 GPa. Neither phase transitions nor amorphization has been observed in such pressure range, demonstrating good lattice stability of CTO. These results have been validated by both the Jahn-Teller effect and Fermi resonance. More importantly, we have attempted to elucidate the evolution of Raman signals for a pressure gauge based on the synergistic effect of plasmon-resonance field enhancement. Our findings not only provide direct experimental evidence that CTO stays phase stable up to 40 GPa, but also offer insight to understanding the high-pressure Raman behaviors for other ilmenite based functional materials.