CaMn₂O₄ is of interest for use as a cathode in Ca ion batteries. Two structures can be prepared the first is orthorhombic and is based on edge-sharing chains of MnO₆ octahedra. The second is tetragonal and contains corner sharing MnO₆ octahedra. The volumes of the MnO₆ octahedra are 11.82 and 8.89 Å3, respectively

(a) Which of the two structures, orthorhombic or tetragonal, is likely to be stable at high pressures? 

(b) Giving your reasoning predict if the transformation between the two structures is likely to be first order or continuous.