Phase transitions and related properties of organic-inorganic hybrid materials

Abstract

Organic-inorganic hybrid perovskite materials incorporate inorganic as well as organic moieties into a single monolithic nanocomposite structure. Generally the crystals adopt a high degree of order through self-assembly which results from the various bonding interactions.Organic-inorganic aliphatic hybrid crystals are generally represented by the formula: [(CnH2n+1)NH3]2 MX4. These hybrid structures are characterized by an alternating structure where the ionic, inorganic metal halide layers are sandwiched between paraffinic alkylammonium chains (Ciajoloet al.1977; Zuniga et al. 1983; Guoet al. 1995). This study was based around hybrid materials containing a range of aliphatic amines and the divalent metals:Copper, Cobalt, Zinc, Mercury and Lead. The hybrid crystals that were synthesized in this study were structurally and thermally characterized as a majority of the structures were novel. The coordination of the inorganic metal-halide component was determined by the divalent metal centre. The divalent zinc, mercury and cobalt centers which were ionically bonded to chlorine, bromine or iodine tended to form isolated tetrahedral units. The zinc (II) chloride hybrid crystals however had the ability to coordinate as either isolated octahedral or isolated tetrahedral units. The lead and cadmium hybrid crystals coordinated as corner sharing octahedral units which extended along two dimensions. The packing characteristics of the cationic organic chains were directly influenced by the coordination and dimensionality of the inorganic component. The hybrid crystals were thermally characterized as they tend to exhibit a number of phase transitions such as solid-solid phase transitions and order-disorder transitions. Some hybrid crystals proved to be more stable than others when exposed to various atmospheric conditions. Overall the iodine containing crystals were not as stable as they tended to oxidized and degraded easily. The mercury containing crystals were also quite unstablewhen exposed to the atmosphere.