Melting of an anchored bilayer: phase transitions in the organic-inorganic hybrid pervoskite (CH3NH3)(CH3(CH2)nNH3)2Pb2I7 (n = 11, 13, 15, 17)

Barman, S. ; Vasudevan, S. (2009) Melting of an anchored bilayer: phase transitions in the organic-inorganic hybrid pervoskite (CH3NH3)(CH3(CH2)nNH3)2Pb2I7 (n = 11, 13, 15, 17) Journal of Physical Chemistry C, 113 (35). pp. 15698-15706. ISSN 1932-7447

Full text not available from this repository.

Official URL: http://pubs.acs.org/doi/abs/10.1021/jp903840j

Related URL: http://dx.doi.org/10.1021/jp903840j

Abstract

The conformation, organization, and phase transitions of alkyl chains in organic-inorganic hybrids based on the double pervoskite-slab lead iodides, (CH3NH3)(CH3(CH2)nNH3)2Pb2I7 (n = 11, 13, 15, 17) have been investigated by X-ray diffraction, calorimetry, and infrared vibrational spectroscopy. In these hybrid solids, double pervoskite (CH3NH3)Pb2I7 slabs are interleaved with alkyl ammonium chains with the anchored alkyl chains arranged as tilted bilayers and adopting a planar all-trans conformation at room temperature. The (CH3NH3)(CH3(CH2) nNH3)2Pb2I7 compounds exhibit a single reversible phase transition above room temperature with the associated enthalpy change varying linearly with alkyl chain length. This transition corresponds to the melting in two-dimensions of the alkyl chains of the anchored bilayer and is characterized by increased conformational disorder of the methylene units of the chain and loss of tilt angle coherence leading to an increase in the interslab spacing. By monitoring features in the infrared spectra that are characteristic of the global conformation of the alkyl chains, a quantitative relation between conformational disorder and melting of the anchored bilayer is established. It is found that, irrespective of the alkyl chain length, melting occurs when at least 60% of the chains in the anchored bilayer of (CH3NH3)(CH3(CH2) nNH3)2Pb2I7 have one or more gauche defects. This concentration is determined by the underlying lattice to which the alkyl chains are anchored.

Item Type:Article
Source:Copyright of this article belongs to American Chemical Society.
ID Code:58434
Deposited On:31 Aug 2011 06:08
Last Modified:31 Aug 2011 06:08

Repository Staff Only: item control page