Phase changes in lithium amide–borohydride complexes under high pressure

Raman and powder X-ray diffraction measurements have been used to investigate the various phases of Li4(BH4)(NH2)3 and Li2(BH4)(NH2) under high temperature and high pressure. In Li4(BH4)(NH2)3, the ambient pressure phase (phase I) transforms to a high pressure phase (phase II) at around 17 GPa at room temperature. The phase boundary between the two phases has a negative slope against pressure, and the difference in ionic conductivity between the phases is small around the phase boundary at 2.9 GPa. In Li2(BH4)(NH2), two high-pressure and high-temperature phases (HPHT1, HPHT2) have been found at around 400 K at high pressures. Based on powder X-ray diffraction and DFT calculation, the HPHT1 and the HPHT2 phases have been estimated to be orthorhombic structures with space groups of Pbam and Imma, respectively.