An investigation of the structural phase transition of ammonia borane

A detailed anelastic spectroscopy study of the structural phase transition of ammonia borane was conducted for the first time. The transformation from the tetragonal high temperature phase into the orthorhombic low temperature one is detected on cooling around 220 K by a huge drop of the elastic modulus and a spike of the elastic energy dissipation. We find clear indications of a hysteresis, which led us to conclude that the transition is of first-order. The kinetics of the transition was investigated in detail.