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Silva RX, Hora RR, Nonato A, García-Fernández A, Salgado-Beceiro J, Señarís-Rodríguez MA, Andújar MS, Ayala AP, Paschoal CWA. Order-disorder phase transition and molecular dynamics in the hybrid perovskite [(CH 3) 3NH][Mn(N 3) 3]. SPECTROCHIMICA ACTA. PART A, MOLECULAR AND BIOMOLECULAR SPECTROSCOPY 2023; 289:122198. [PMID: 36502746 DOI: 10.1016/j.saa.2022.122198] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/12/2022] [Revised: 11/08/2022] [Accepted: 11/27/2022] [Indexed: 06/17/2023]
Abstract
We present a temperature-dependent Raman scattering study of a [(CH3)3NH][Mn(N3)3] hybrid organic-inorganic azide-perovskite, in which we have analysed in detail the wavenumber and full width at half-maximum (FWHM) of lattice modes and internal modes of the NC3 skeleton, N3- and CH3 molecular groups. In general, the modes exhibited unusual behaviour during the phase transitions, including discontinuity in the phonon wavenumber, bandwidth, and unconventional shifts upon temperature variation. Spectral features on heating reveal the absence of significant distortions in the NC3 skeleton and a relatively restricted order-disorder process of the TrMA+ cations. On the other hand, linewidth anomalies of the δNC3 and νasNC3 modes have been attributed to the molecular dynamics of encapsulated cations. The unconventional blue shift of the symmetric stretching modes of azide ligands indicates the weakening of the intermolecular interactions between the TrMA+ cations and azido-bridges, and the strengthening of the intramolecular bonds. Additionally, we have used differential scanning calorimetry to confirm the subtle monoclinic to monoclinic (P21/c → C2/c) phase transition at around 330 K; and the phase transition to trigonal structure (R3¯m) above 359 K, whose associated entropy variation turns to be |ΔS| ∼ 22.3 J·kg-1 K-1 and displays a barocaloric (BC) tunability |δTt/δP| ∼ 3.17 K kbar-1, according to our estimations using the Clausius-Clapeyron method. Although the obtained values of entropy change and BC tunability are very close to those reported on formate-perovskites and other important caloric materials, those parameters are much lower than the giant entropy change of ∼80 Jkg-1 K-1 and large BC tunability ∼12 K kbar-1 observed for the analogue azide-perovskite [(CH3)4N][Mn(N3)]3 (TMAMnN3). Very interestingly, our combined study shed light to understand such different behaviour, as they reveal that the hydrogen bonds created between the TrMA+ cations and the framework prevent an extensive order-disorder process that is needed to obtain large entropy changes and large BC coefficients as it occurs in the case of related azide-perovskites with no H-bonds between the A cations (for example TMA) and the framework.
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Affiliation(s)
- R X Silva
- Departamento de Física, Universidade Federal do Ceará, Campus do Pici, 65455-900 Fortaleza, CE, Brazil; Coordenação de Ciências Naturais, Universidade Federal do Maranhão, Campus de Codó, 65400-000 Codó, MA, Brazil.
| | - R R Hora
- Departamento de Física, Universidade Federal do Ceará, Campus do Pici, 65455-900 Fortaleza, CE, Brazil
| | - A Nonato
- Coordenação de Ciências Naturais, Universidade Federal do Maranhão, Campus de Bacabal, 65700-000 Bacabal, MA, Brazil
| | - Alberto García-Fernández
- Grupo QuiMolMat, Departamento de Química Fundamental, Facultad de Ciencias y CICA, Universidade da Coruña, Campus A Coruña, 15071 A Coruña, Spain
| | - Jorge Salgado-Beceiro
- Grupo QuiMolMat, Departamento de Química Fundamental, Facultad de Ciencias y CICA, Universidade da Coruña, Campus A Coruña, 15071 A Coruña, Spain
| | - María Antonia Señarís-Rodríguez
- Grupo QuiMolMat, Departamento de Química Fundamental, Facultad de Ciencias y CICA, Universidade da Coruña, Campus A Coruña, 15071 A Coruña, Spain
| | - Manuel Sánchez Andújar
- Grupo QuiMolMat, Departamento de Química Fundamental, Facultad de Ciencias y CICA, Universidade da Coruña, Campus A Coruña, 15071 A Coruña, Spain
| | - A P Ayala
- Departamento de Física, Universidade Federal do Ceará, Campus do Pici, 65455-900 Fortaleza, CE, Brazil
| | - C W A Paschoal
- Departamento de Física, Universidade Federal do Ceará, Campus do Pici, 65455-900 Fortaleza, CE, Brazil
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Abstract
A survey of the rigid unit modes in molecular perovskites is presented, showing how the prevalence of conventional tilts, unconventional tilts and columnar shifts vary across the different classes of molecular perovskites.
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Affiliation(s)
- Hanna L. B. Boström
- Department of Inorganic Chemistry
- Ångström Laboratory
- Uppsala Universitet
- 751 21 Uppsala
- Sweden
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