title: Phase Transition, Dielectric Properties, and Ionic Transport in the [(CH3)2NH2]PbI3Organic-Inorganic Hybrid with 2H-Hexagonal Perovskite Structure.
abstract: In this work, we focus on [(CH3)2NH2]PbI3, a member of the [AmineH]PbI3series of hybrid organic-inorganic compounds, reporting a very easy mechanosynthesis route for its preparation at room temperature. We report that this [(CH3)2NH2]PbI3compound with 2H-perovskite structure experiences a first-order transition at ≈250 K from hexagonal symmetry P63/mmc (HT phase) to monoclinic symmetry P21/c (LT phase), which involves two cooperative processes: an off-center shift of the Pb2+cations and an order-disorder process of the N atoms of the DMA cations. Very interestingly, this compound shows a dielectric anomaly associated with the structural phase transition. Additionally, this compound displays very large values of the dielectric constant at room temperature because of the appearance of a certain conductivity and the activation of extrinsic contributions, as demonstrated by impedance spectroscopy. The large optical band gap displayed by this material (Eg= 2.59 eV) rules out the possibility that the observed conductivity can be electronic and points to ionic conductivity, as confirmed by density functional theory calculations that indicate that the lowest activation energy of 0.68 eV corresponds to the iodine anions, and suggests the most favorable diffusion paths for these anions. The obtained results thus indicate that [(CH3)2NH2]PbI3is an electronic insulator and an ionic conductor, where the electronic conductivity is disfavored because of the low dimensionality of the [(CH3)2NH2]PbI3structure.
authors.affiliation: QuiMolMat Group, Department of Fundamental Chemistry, Faculty of Science and CICA, University of A Coruña , Campus A Coruña, 15071 A Coruña, Spain.
authors.forename: A
authors.initials: A
authors.lastname: García-Fernández
authors.affiliation: QuiMolMat Group, Department of Fundamental Chemistry, Faculty of Science and CICA, University of A Coruña , Campus A Coruña, 15071 A Coruña, Spain.
authors.forename: J M
authors.initials: JM
authors.lastname: Bermúdez-García
authors.affiliation: QuiMolMat Group, Department of Fundamental Chemistry, Faculty of Science and CICA, University of A Coruña , Campus A Coruña, 15071 A Coruña, Spain.
authors.forename: S
authors.initials: S
authors.lastname: Castro-García
authors.affiliation: RIAIDT X-ray Unit, University of Santiago de Compostela , 15782 Santiago de Compostela, Spain.
authors.forename: A L
authors.identifier: http://orcid.org/0000-0002-8203-3791
authors.initials: AL
authors.lastname: Llamas-Saiz
authors.affiliation: Department of Industrial Engineering II, University of A Coruña , Campus Ferrol, 15403 Ferrol, Spain.
authors.forename: R
authors.initials: R
authors.lastname: Artiaga
authors.affiliation: Department of Industrial Engineering II, University of A Coruña , Campus Ferrol, 15403 Ferrol, Spain.
authors.forename: J
authors.initials: J
authors.lastname: López-Beceiro
authors.affiliation: International Centre for Quantum and Molecular Structures, Physics Department, Shanghai University , Shanghai 200444, China.|Materials Genome Institute and Shanghai Key Laboratory of High Temperature Superconductors, Shanghai University , Shanghai 200444, China.
authors.forename: S
authors.initials: S
authors.lastname: Hu
authors.affiliation: International Centre for Quantum and Molecular Structures, Physics Department, Shanghai University , Shanghai 200444, China.|Materials Genome Institute and Shanghai Key Laboratory of High Temperature Superconductors, Shanghai University , Shanghai 200444, China.
authors.forename: W
authors.initials: W
authors.lastname: Ren
authors.affiliation: International Centre for Quantum and Molecular Structures, Physics Department, Shanghai University , Shanghai 200444, China.|Consiglio Nazionale delle Ricerche , Institute CNR-SPIN , Via Vetoio, 67100 L'Aquila, Italy.
authors.forename: A
authors.initials: A
authors.lastname: Stroppa
authors.affiliation: QuiMolMat Group, Department of Fundamental Chemistry, Faculty of Science and CICA, University of A Coruña , Campus A Coruña, 15071 A Coruña, Spain.
authors.forename: M
authors.identifier: http://orcid.org/0000-0002-3441-0994
authors.initials: M
authors.lastname: Sánchez-Andújar
authors.affiliation: QuiMolMat Group, Department of Fundamental Chemistry, Faculty of Science and CICA, University of A Coruña , Campus A Coruña, 15071 A Coruña, Spain.
authors.forename: M A
authors.initials: MA
authors.lastname: Señarís-Rodríguez