Group Theory Analysis to Study Phase Transitions of Quasi-2D Sr<sub>3</sub>Hf<sub>2</sub>O<sub>7</sub>
Estelina Lora da Silva,
Adeleh Mokhles Gerami,
P. Neenu Lekshmi,
Michel L. Marcondes,
Lucy V. C. Assali,
Helena M. Petrilli,
Joao Guilherme Correia,
Armandina M. L. Lopes,
João P. Araújo
Affiliations
Estelina Lora da Silva
IFIMUP, Institute of Physics for Advanced Materials, Nanotechnology and Photonics, Department of Physics and Astronomy, Faculty of Sciences, University of Porto, Rua do Campo Alegre 687, 4169-007 Porto, Portugal
Adeleh Mokhles Gerami
School of Particles and Accelerators, Institute for Research in Fundamental Sciences (IPM), P.O. Box 19395-5531 Tehran, Iran
P. Neenu Lekshmi
IFIMUP, Institute of Physics for Advanced Materials, Nanotechnology and Photonics, Department of Physics and Astronomy, Faculty of Sciences, University of Porto, Rua do Campo Alegre 687, 4169-007 Porto, Portugal
Michel L. Marcondes
Instituto de Física, Universidade de São Paulo, Rua do Matao 1371, São Paulo 05508-090, Brazil
Lucy V. C. Assali
Instituto de Física, Universidade de São Paulo, Rua do Matao 1371, São Paulo 05508-090, Brazil
Helena M. Petrilli
Instituto de Física, Universidade de São Paulo, Rua do Matao 1371, São Paulo 05508-090, Brazil
Joao Guilherme Correia
CERN, Esplanade des Particules 1, 1211 Geneva 23, Switzerland
Armandina M. L. Lopes
IFIMUP, Institute of Physics for Advanced Materials, Nanotechnology and Photonics, Department of Physics and Astronomy, Faculty of Sciences, University of Porto, Rua do Campo Alegre 687, 4169-007 Porto, Portugal
João P. Araújo
IFIMUP, Institute of Physics for Advanced Materials, Nanotechnology and Photonics, Department of Physics and Astronomy, Faculty of Sciences, University of Porto, Rua do Campo Alegre 687, 4169-007 Porto, Portugal
We present an ab-initio study performed in the framework of density functional theory, group-subgroup symmetry analysis and lattice dynamics, to probe the octahedral distortions, which occur during the structural phase transitions of the quasi-2D layered perovskite Sr3Hf2O7 compound. Such a system is characterized by a high-temperature I4/mmm centrosymmetric structure and a ground-state Cmc21 ferroelectric phase. We have probed potential candidate polymorphs that may form the I4/mmm → Cmc21 transition pathways, namely Fmm2, Ccce, Cmca and Cmcm. We found that the band gap widths increase as the symmetry decreases, with the ground-state structure presenting the largest gap width (∼5.95 eV). By probing the Partial Density of States, we observe a direct relation regarding the tilts and rotations of the oxygen perovskite cages as the transition occurs; these show large variations mostly of the O p-states which contribute mostly to the valence band maximum. Moreover, by analyzing the hyperfine parameters, namely the Electric Field Gradients and asymmetric parameters, we observe variations as the transition occurs, from which it is possible to identify the most plausible intermediate phases. We have also computed the macroscopic polarization and confirm that the Cmc21 phase is ferroelectric with a value of spontaneous polarization of 0.0478 C/m2. The ferroelectricity of the ground-state Cmc21 system arises due to a second order parameter related to the coupling of the rotation and tilts of the O perovskite cages together with the Sr displacements.
