{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2026,1,15]],"date-time":"2026-01-15T08:56:32Z","timestamp":1768467392716,"version":"3.49.0"},"reference-count":56,"publisher":"MDPI AG","issue":"4","license":[{"start":{"date-parts":[[2021,3,31]],"date-time":"2021-03-31T00:00:00Z","timestamp":1617148800000},"content-version":"vor","delay-in-days":0,"URL":"https:\/\/creativecommons.org\/licenses\/by\/4.0\/"}],"funder":[{"DOI":"10.13039\/501100001871","name":"Funda\u00e7\u00e3o para a Ci\u00eancia e a Tecnologia","doi-asserted-by":"publisher","award":["NORTE-01-0145-FEDER-022096"],"award-info":[{"award-number":["NORTE-01-0145-FEDER-022096"]}],"id":[{"id":"10.13039\/501100001871","id-type":"DOI","asserted-by":"publisher"}]},{"DOI":"10.13039\/501100001871","name":"Funda\u00e7\u00e3o para a Ci\u00eancia e a Tecnologia","doi-asserted-by":"publisher","award":["POCI-01-0145-FEDER-029454"],"award-info":[{"award-number":["POCI-01-0145-FEDER-029454"]}],"id":[{"id":"10.13039\/501100001871","id-type":"DOI","asserted-by":"publisher"}]},{"DOI":"10.13039\/501100001871","name":"Funda\u00e7\u00e3o para a Ci\u00eancia e a Tecnologia","doi-asserted-by":"publisher","award":["POCI-01-0145-FEDER-032527"],"award-info":[{"award-number":["POCI-01-0145-FEDER-032527"]}],"id":[{"id":"10.13039\/501100001871","id-type":"DOI","asserted-by":"publisher"}]},{"DOI":"10.13039\/100012470","name":"CERN","doi-asserted-by":"publisher","award":["CERN\/FIS-PAR\/0005\/2017"],"award-info":[{"award-number":["CERN\/FIS-PAR\/0005\/2017"]}],"id":[{"id":"10.13039\/100012470","id-type":"DOI","asserted-by":"publisher"}]},{"DOI":"10.13039\/501100001807","name":"Funda\u00e7\u00e3o de Amparo \u00e0 Pesquisa do Estado de S\u00e3o Paulo","doi-asserted-by":"publisher","award":["2018\/07760-4"],"award-info":[{"award-number":["2018\/07760-4"]}],"id":[{"id":"10.13039\/501100001807","id-type":"DOI","asserted-by":"publisher"}]},{"DOI":"10.13039\/501100001807","name":"Funda\u00e7\u00e3o de Amparo \u00e0 Pesquisa do Estado de S\u00e3o Paulo","doi-asserted-by":"publisher","award":["2019\/07661-9"],"award-info":[{"award-number":["2019\/07661-9"]}],"id":[{"id":"10.13039\/501100001807","id-type":"DOI","asserted-by":"publisher"}]},{"DOI":"10.13039\/501100003593","name":"Conselho Nacional de Desenvolvimento Cient\u00edfico e Tecnol\u00f3gico","doi-asserted-by":"publisher","award":["305753\/2017-7"],"award-info":[{"award-number":["305753\/2017-7"]}],"id":[{"id":"10.13039\/501100003593","id-type":"DOI","asserted-by":"publisher"}]},{"DOI":"10.13039\/501100003593","name":"Conselho Nacional de Desenvolvimento Cient\u00edfico e Tecnol\u00f3gico","doi-asserted-by":"publisher","award":["311373\/2018-6"],"award-info":[{"award-number":["311373\/2018-6"]}],"id":[{"id":"10.13039\/501100003593","id-type":"DOI","asserted-by":"publisher"}]}],"content-domain":{"domain":[],"crossmark-restriction":false},"short-container-title":["Nanomaterials"],"abstract":"<jats:p>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 \u2192 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 (\u223c5.95 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.<\/jats:p>","DOI":"10.3390\/nano11040897","type":"journal-article","created":{"date-parts":[[2021,3,31]],"date-time":"2021-03-31T21:37:03Z","timestamp":1617226623000},"page":"897","update-policy":"https:\/\/doi.org\/10.3390\/mdpi_crossmark_policy","source":"Crossref","is-referenced-by-count":9,"title":["Group Theory Analysis to Study Phase Transitions of Quasi-2D Sr3Hf2O7"],"prefix":"10.3390","volume":"11","author":[{"ORCID":"https:\/\/orcid.org\/0000-0002-7093-3266","authenticated-orcid":false,"given":"Estelina Lora","family":"da Silva","sequence":"first","affiliation":[{"name":"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"}]},{"given":"Adeleh Mokhles","family":"Gerami","sequence":"additional","affiliation":[{"name":"School of Particles and Accelerators, Institute for Research in Fundamental Sciences (IPM), P.O. Box 19395-5531 Tehran, Iran"},{"name":"CERN, Esplanade des Particules 1, 1211 Geneva 23, Switzerland"}]},{"given":"P. Neenu","family":"Lekshmi","sequence":"additional","affiliation":[{"name":"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"}]},{"ORCID":"https:\/\/orcid.org\/0000-0002-9383-6186","authenticated-orcid":false,"given":"Michel L.","family":"Marcondes","sequence":"additional","affiliation":[{"name":"Instituto de F\u00edsica, Universidade de S\u00e3o Paulo, Rua do Matao 1371, S\u00e3o Paulo 05508-090, Brazil"}]},{"ORCID":"https:\/\/orcid.org\/0000-0001-7772-4486","authenticated-orcid":false,"given":"Lucy V. C.","family":"Assali","sequence":"additional","affiliation":[{"name":"Instituto de F\u00edsica, Universidade de S\u00e3o Paulo, Rua do Matao 1371, S\u00e3o Paulo 05508-090, Brazil"}]},{"ORCID":"https:\/\/orcid.org\/0000-0002-7275-3357","authenticated-orcid":false,"given":"Helena M.","family":"Petrilli","sequence":"additional","affiliation":[{"name":"Instituto de F\u00edsica, Universidade de S\u00e3o Paulo, Rua do Matao 1371, S\u00e3o Paulo 05508-090, Brazil"}]},{"given":"Joao Guilherme","family":"Correia","sequence":"additional","affiliation":[{"name":"CERN, Esplanade des Particules 1, 1211 Geneva 23, Switzerland"},{"name":"C2TN, Departamento de Engenharia e Ci\u00eancias Nucleares, Instituto Superior T\u00e9cnico, Universidade de Lisboa, Estrada Nacional 10, 2695-066 Bobadela, Portugal"}]},{"given":"Armandina M. L.","family":"Lopes","sequence":"additional","affiliation":[{"name":"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"}]},{"ORCID":"https:\/\/orcid.org\/0000-0002-1646-7727","authenticated-orcid":false,"given":"Jo\u00e3o P.","family":"Ara\u00fajo","sequence":"additional","affiliation":[{"name":"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"}]}],"member":"1968","published-online":{"date-parts":[[2021,3,31]]},"reference":[{"key":"ref_1","doi-asserted-by":"crossref","first-page":"407","DOI":"10.1038\/nmat4168","article-title":"Experimental demonstration of hybrid improper ferroelectricity and the presence of abundant charged walls in (Ca,Sr)3Ti2O7 crystals","volume":"14","author":"Oh","year":"2015","journal-title":"Nat. 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