Discovered in 1839 by Rose, Perovskites are materials being studied since a long time. Only in 1925, with the emerging of X-Ray techniques, Goldsmith discovered the Face-Centered-Cubic (FCC) crystallographic structure of CaTiO3, nowadays known as the reference structure of these materials. Due to their super conductivity, magneto-resistance and oxygen mobility properties, these materials are currently employed for a wide range of applications: Solid Oxide Fuel Cells (SOFC), Photovoltaic (PV), Oxygen Sensors (OS) and Oxygen-Transporting Membranes (OTM). Because of their incredible properties and wide application field, this thesis aims to study atomic oxygen mobility of La2CoO4 Riddlesden-Popper (RP) phase Perovskite-related material. In this work stability analysis, band structure, Density of States (DOS) and vibrational spectra were computed on both La2CoO4 and La2CoO4.25 RP systems by using Density Functional Theory (DFT) approach implemented with B3LYP functional and both DZVP and TZ basis set for both Oxygen and Cobalt, while for Lanthanum a pseudo-potential basis set was employed. Furthermore, the atomic oxygen mobility was studied with Born-Oppenheimr-Molecular-Dynamic (BOMD) with NVT ensembles at T=300, 700 and 900K. In agreement with recent experimental results, ours shows the tilting of CO6 octahedra with the consequent ordering disappearance in La2CoO4.25 and the most stable antiferromagnetic structure in up-up Cobalt spin orientation. Additionally, the oxygen atom insertion energy into La2CoO4.25 is -7.0 eV, reduced by -1.07 eV compared to other computational methods. The vibrational studies of both RP structures show higher vibrational intensities, for both IR and Raman spectra, from La2CoO4.25 with the appearance of Raman bands in 400-600cm-1 range due to CoO6 octahedra tilting. Furthermore, our dynamic study reveals the jump of apical oxygen atom from one octahedron to an adjacent one, occurring within the layer that is not contiguous to the layer housing the oxygen atom occupying an interstitial position.
Discovered in 1839 by Rose, Perovskites are materials being studied since a long time. Only in 1925, with the emerging of X-Ray techniques, Goldsmith discovered the Face-Centered-Cubic (FCC) crystallographic structure of CaTiO3, nowadays known as the reference structure of these materials. Due to their super conductivity, magneto-resistance and oxygen mobility properties, these materials are currently employed for a wide range of applications: Solid Oxide Fuel Cells (SOFC), Photovoltaic (PV), Oxygen Sensors (OS) and Oxygen-Transporting Membranes (OTM). Because of their incredible properties and wide application field, this thesis aims to study atomic oxygen mobility of La2CoO4 Riddlesden-Popper (RP) phase Perovskite-related material. In this work stability analysis, band structure, Density of States (DOS) and vibrational spectra were computed on both La2CoO4 and La2CoO4.25 RP systems by using Density Functional Theory (DFT) approach implemented with B3LYP functional and both DZVP and TZ basis set for both Oxygen and Cobalt, while for Lanthanum a pseudo-potential basis set was employed. Furthermore, the atomic oxygen mobility was studied with Born-Oppenheimr-Molecular-Dynamic (BOMD) with NVT ensembles at T=300, 700 and 900K. In agreement with recent experimental results, ours shows the tilting of CO6 octahedra with the consequent ordering disappearance in La2CoO4.25 and the most stable antiferromagnetic structure in up-up Cobalt spin orientation. Additionally, the oxygen atom insertion energy into La2CoO4.25 is -7.0 eV, reduced by -1.07 eV compared to other computational methods. The vibrational studies of both RP structures show higher vibrational intensities, for both IR and Raman spectra, from La2CoO4.25 with the appearance of Raman bands in 400-600cm-1 range due to CoO6 octahedra tilting. Furthermore, our dynamic study reveals the jump of apical oxygen atom from one octahedron to an adjacent one, occurring within the layer that is not contiguous to the layer housing the oxygen atom occupying an interstitial position.
Studio quanto-meccanico statico e dinamico per la mobilità di ossigeno nei materiali perovskite-related – il caso del La2CoO4
MASSAFRA, ROSANGELA
2022/2023
Abstract
Discovered in 1839 by Rose, Perovskites are materials being studied since a long time. Only in 1925, with the emerging of X-Ray techniques, Goldsmith discovered the Face-Centered-Cubic (FCC) crystallographic structure of CaTiO3, nowadays known as the reference structure of these materials. Due to their super conductivity, magneto-resistance and oxygen mobility properties, these materials are currently employed for a wide range of applications: Solid Oxide Fuel Cells (SOFC), Photovoltaic (PV), Oxygen Sensors (OS) and Oxygen-Transporting Membranes (OTM). Because of their incredible properties and wide application field, this thesis aims to study atomic oxygen mobility of La2CoO4 Riddlesden-Popper (RP) phase Perovskite-related material. In this work stability analysis, band structure, Density of States (DOS) and vibrational spectra were computed on both La2CoO4 and La2CoO4.25 RP systems by using Density Functional Theory (DFT) approach implemented with B3LYP functional and both DZVP and TZ basis set for both Oxygen and Cobalt, while for Lanthanum a pseudo-potential basis set was employed. Furthermore, the atomic oxygen mobility was studied with Born-Oppenheimr-Molecular-Dynamic (BOMD) with NVT ensembles at T=300, 700 and 900K. In agreement with recent experimental results, ours shows the tilting of CO6 octahedra with the consequent ordering disappearance in La2CoO4.25 and the most stable antiferromagnetic structure in up-up Cobalt spin orientation. Additionally, the oxygen atom insertion energy into La2CoO4.25 is -7.0 eV, reduced by -1.07 eV compared to other computational methods. The vibrational studies of both RP structures show higher vibrational intensities, for both IR and Raman spectra, from La2CoO4.25 with the appearance of Raman bands in 400-600cm-1 range due to CoO6 octahedra tilting. Furthermore, our dynamic study reveals the jump of apical oxygen atom from one octahedron to an adjacent one, occurring within the layer that is not contiguous to the layer housing the oxygen atom occupying an interstitial position.I documenti in UNITESI sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
https://hdl.handle.net/20.500.14240/146802