Bipyramidal distortions play the governing role in physical properties of HoMnO$_3$ multiferroics. We have carried out angle-dispersive high pressure synchrotron X-ray diffraction experiments on hexagonal HoMnO$_3$ to find the evolution of bipyramidal parameters upon external compression. It is found that the average bond-lengths and bond-angles between Mn and O atoms depict significant reduction, which results in the distortion in MnO$_5$ bipyramidal structure athigh pressures. Further, since subtle variations in these distortions are used to compare the properties of hexagonal HoMnO$_3$ manganite series, in-situ low temperature infrared spectroscopic studies of 10% Dy-doped HoMnO$_3$ have beencarried out to study the effect of further increase in R-site cationic radius on MnO$_5$ deformations. It is found that the phonon modes specifically related to the motion of Mn and O atoms in ab-plane display irregularities near magnetic transition temperatures ($T_N$ and T$_{SR}$) via spin phonon coupling. Even a small increase in average ionic radius of rare-earth atom suppresses this anomalous behaviour and follows the trend of undoped hexagonal rare-earth manganites.

We report high pressure studies on an organic perchlorate system diglycine perchlorate (DGPCl) up to 15 GPa. Single crystals of DGPCl were studied using high pressure Raman spectroscopy, which show discontinuous spectral changes at two pressures across ${\sim}$1.8 and ${\sim}$9 GPa. While the low pressure phase transition is primarily governed by the reorientational changes in organic groups and the corresponding hydrogen bonds, the high pressure transition involves substantial changes in Raman spectroscopic features of the perchlorate group. The splitting of the characteristic and the most intense Raman mode, i.e., perchlorate symmetric stretching mode, above 9 GPa suggests modifications in perchlorate group local structure. The structural changes are found to be reversible upon pressure release.