Temperature and Pressure Induced Phase Transitions in the Perovskite-Type Layer Compound (CH3-NH3)2 CdCl4

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Abstract
The phase diagram of (CH3NH3)2 CdCl4 has been established by means of a Raman scattering study under hydrostatic pressures ranging from 0 to 6 Kbars, and at different temperatures between 80 and 300 K. The phase sequence observed for this compound at ambient pressure is shown to be related not only to the reorientational dynamics of the CH3NH3 + groups, but also to disordering processes involving the CdCl6, octahedra. Increasing pressure causes the appearance of a new high pressure phase (HP). It is suggested that HP is an ordered phase and that its structure results from anti-phase slips of the perovskite layers.