Transport measurements were performed on over-doped samples of pristine and Pb-substituted Bi–Sr–Ca–Cu–O as a function of applied pressure up to 7 GPa. A monotonic decrease in the superconducting transition temperature accompanied by a change in the normal-state behaviour from metallic to semiconducting as a function of pressure is observed in the pristine sample. In the Pb-substituted sample, a monotonic decrease in the superconducting transition temperature up to ${\sim}$4.5 GPa followed by an increase after attaining a valley is observed. The pressure required to achieve this increase in T$_C$ in the Pb-substituted Bi–Sr–Ca–Cu–O was found to be much lower than that reported in the literature. High-pressure X-ray diffraction measurements performed on these samples reveal the absence of any structural phase transition. Furthermore, the values of the bulk moduli are found to increase in the Pb-substituted sample. The density functional theory calculations used to substantiate the obtained results indicate a pressure-induced buckling of the Cu–O plane in the Bi-2212 phase of the pristine sample. In the Pb-substituted sample, an increase in the number of electronic states available for conduction at the Fermi level and a pressure-dependent increase in the contribution of Pb towards the density of states are revealed from the calculations of the density functional theory.

Rare-earth uranates-RE$_6$UO$_{12}$ are synthesized by heating mixture of uranium oxide and rare-earth oxides in 1:6 ratio above 1273 K. These compounds stabilize in rhombohedral structure at ambient. High-pressure (HP) X-ray diffraction studies reveal that the compounds are stable at lower pressures, beyond which disorder is seen to originate and compound has a tendency to amporphize at very HPs. The a-axis of the lattice is found to be more rigid as compared to c-axis because of corner sharing polyhedra along a-axis. Anomalous compressibility behaviour is seen in Gd$_6$UO$_{12}$, where sharp decrease in the bulk modulus is observed. The behaviour is against the normal trend of compressibility in RE$_6$UO$_{12}$ compounds along rare-earth cation series.

High pressure behaviour of core/shell amorphous carbon (a-C) nanostructures was studied using synchrotron X-ray diffraction (XRD) and Raman spectroscopy up to ${\sim}$25 GPa. These nanostructures having spherical a-C shells with ${\gamma}$-Fe$_2$O$_3$ nanoparticles at the core were synthesized by catalyst-assisted lamp black method. The typical size of core (${\gamma}$-Fe$_2$O$_3$)/shell (a-C) is ${\sim}$5 nm/20 nm. Comparative XRD of the core (${\gamma}$-Fe$_2$O$_3$) in opened- and closed-shell (a-C) shows that the carbon shells do not fully transmit the applied high pressure inwards, under hydrostatic conditions. Raman spectroscopy shows that the graphitic G-mode blue shifts reversibly with applied pressure with a coefficient ${\sim}$3.5 cm$^{-1}$ GPa$^{-1}$, which is ${\sim}$25 to 40% less than that for graphite and carbon nanotubes. It is suggested that a rigid and crosslinked structure of the carbon shell might be lossy for the observed pressure drop.