Weakness of ionic bonds and solid decomposition in calcium phosphides under high pressure

In this work, we have investigated the structures and phase transitions of the Ca-P system under high pressure using the first-principles calculation method combined with the CALYPSO structural searching technique. We discovered new phases with the chemometrics of CaxPy (x/y = 1/1, 1/2, 3/2,2/1) and found that Ca3P2 and Ca2P decompose into elemental solid calcium and phosphorus at external pressures of 459 GPa and 478 GPa, respectively. This phenomenon contradicts the common knowledge that pressure usually leads to denser and more stable compound structures. As pressure increases, the Delta PV term of the compound exhibits an upward trend, which serves as the principal cause of Ca3P2 decomposition. We have delved into the electronic properties of Ca3P2, encompassing Bader charge, Madelung energy, band structures, Electron Localization Function (ELF), and ICOHP. The findings give evidence that the abatement of inter-ionic interaction, triggered by pressure, constitutes the foremost factor inducing Ca-P compounds composition into solid elements. Our research eluci-dates how high pressure regulates Ca-P compounds behavior and electronic properties, and offers valuable insight into the behavioral transformations of other alkaline-earth metal phosphides under high pressure.