Pressure-Induced Stable Beryllium Peroxide.

Beryllium oxides, at ambient pressure, have been extensively studied due to their unique chemical bonds and applications. However, the long-desirable target beryllium peroxide (BeO2 ) has not been reported, thus far. Currently, the application of pressure has become a powerful tool in finding unusual stoichiometric compounds with exotic properties. Here, swarm structural searches in combination with first-principles calculations disclosed that the reaction of BeO and oxygen, at pressures above 89.6 GPa, yields BeO2 . Interestingly, this reaction pressure is lower than the phase transition pressure (106 GPa) of pure BeO. BeO2 crystallizes in FeS2 -type structure, whose remarkable feature is that it contains peroxide group (O2 2- ) with an O-O distance of 1.40 Å at 100 GPa. Notably, O2 2- is maintained in the pressure range of 89.6-300 GPa. The chemical bonding analysis shows that the uniformly distributed ionic Be-O and covalent O-O bonding network plays a key role in determining its structural stability. BeO2 is a direct band gap nonmetal, and its band gap becomes larger with increase of pressure, which is in sharp contrast with BaO2 . Moreover, phase diagram of Be-O binary compounds with various Bex Oy (x = 1-3, y = 1-6) compositions at pressures of up to 300 GPa was reliably built. Our results are also important for enriching the understanding of beryllium oxides.