We investigate the permittivity of helium (He) in perovskite-group ${\mathrm{KNbO}}_3$ and its high-pressure polymorphs using Raman scattering. Samples were loaded into either an argon (Ar) or He pressure medium to fingerprint the incorporation of He. Specifically, our high-pressure in situ Raman spectroscopy experiments reveal that He has permeated into the high-pressure tetragonal and cubic perovskite phases, while the ambient orthorhombic phase can hold little He. In contrast, Ar is impermeable into ${\mathrm{KNbO}}_3$ under pressure and the results are consistent with previous studies. We further validate the incorporation of He into the lattice sites of ${\mathrm{KNbO}}_3$ by using both the disorder effect and Fano resonance analyses. The structural selectivity behavior of He suggests that minerals could potentially induce He concentration heterogeneity within Earth's interior.

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• Geophysics
• High-pressure studies
• Phase transitions
• Pressure effects
• Perovskites
• Pressure techniques
• Raman spectroscopy