Structural Phase Transitions in KC8 under High Pressure

KC8 displays intriguing phase transitions under varying pressures, making it an ideal candidate for investigation for possible a novel superconductor under pressure with hydrogen. Our findings provide a robust foundation for a broader exploration of carbon-rich compounds featuring sp3 networks. At ambient conditions, KC8 displays a 2x2 phase. As pressure increases from 2.3 GPa to 21 GPa, phase transitions occur along the a and b axes. At 2.3 GPa, a transition to a square root 3 x square root 3 phase is observed, in line with previous data. At 3.0 GPa, the 2x2 phase disappears, while the square root 3 phase persists until 6 GPa. Between 6 GPa and 21 GPa, new phases emerge, but their identification is pending. At 21 GPa, we observe evidence of changes not only in the a and b axes but also in the c axis. Importantly, the compressibility of the c axis, from ambient conditions up to the point just before these transitions, aligns with previously reported data. We have utilized Raman and IR spectroscopy to investigate the incorporation of hydrogen into KC8.