High pressure measurement of the uniaxial stress of host layers on intercalants and staging transformation of intercalation compounds

A layered double-hydroxide intercalation compound was synthesized to measure the uniaxial stress the host layers exert on the intercalants. To measure the uniaxial stress, we employed the photoluminescence (PL) from the intercalated species, the Sm ion complex, as it is sensitive to the deformation of the intercalants. Of the many PL peaks the Sm ion complex produces, the one that is independent of the counter-cation environment was chosen for the measurement since the Sm ion complexes are placed under a different electrostatic environment after intercalation. The peak position of the PL was redshifted linearly with increasing hydrostatic pressure on the intercalated sample. Using this pressure-induced redshifting rate and the PL difference at ambient pressure between the pre-intercalation and the intercalated ions, we found that, in the absence of external pressure, the uniaxial stress exerted on the samarium ion complexes by the host layers was about 13.9 GPa at room temperature. Time-resolved PL data also supported this observation. The uniaxial stress showed a large variation with temperature, decreasing to 7.6 GPa at 28 K. This very unusual behaviour implies that staging transformation towards a higher degree occurs at low temperatures. It was also observed that the redshift rate of the PL was slowed down at higher temperatures. This effect is equivalent to the decreased deformation rate of the intercalants at higher temperatures and is explained by the pressure-induced staging transition