{"id":{"repo_id":"vt","oai_identifier":"oai:vtechworks.lib.vt.edu:10919/37733"},"canonical_url":"https://search.dev.ndltd.org/etd/vt/oai:vtechworks.lib.vt.edu:10919/37733","repository":{"repo_id":"vt","name":"Virginia Tech","base_url":"https://vtechworks.lib.vt.edu/oai/request"},"display":{"title":"Some Aspects of the Crystal Chemistry of Perovskites under High Pressures","abstract":"This thesis makes contributions to the methodology of quantitative description of the tilting systems of perovskite structures and theoretical analysis of high-pressure phase transitions of representative perovskites. Chapter 1 and 2 introduce the perovskite structures, tilting classification and descriptions. The structures in each of the 15 tilt systems have been decomposed in to the amplitudes of symmetry-adapted modes in order to provide a clear and unambiguous definition of the tilt angles. A general expression in terms of tilt angles for the ratio of the volumes of the two polyhedra within the perovskite structure is derived. Chapter 3 uses the first-principles plane-wave pseudopotential calculations to investigate the high-pressure to phase transition and elasticity of LaAlO3 perovskite. This second order transition is determined to occur at ~14 GPa by the pressure variation of the squared frequency of the soft R-point mode in the structure. Elastic moduli are inverted from the calculated stress-strain data by the singular value decomposition method. The Landau parameters for this phase transition are calibrated from the calculation results. Chapter 4 uses the same method to investigate the high-pressure phase transitions and elasticity of YAlO3 perovskite. The Pnma, Imma, I4/mcm, , perovskite structures and the NH4CdCl3-, Gd2S3-, U2S3-, CaIrO3-type structures are considered. A continuous Pnma to Imma transition occurs at ~89 GPa, determined from the soft Z-point mode of the Imma structure. Then, a discontinuous Imma to I4/mcm transition occurs at ~100 GPa, suggested by the relative enthalpies and phonon dispersions. The elasticities of the Pnma, Imma and I4/mcm structures show mechanical stabilities compatible with the phase transitions. The NH4CdCl3- and CaIrO3-type structures are dynamically stable although not energetically favorable. The relative A/B site polyhedral volume ratios are found to qualitatively reproduce the relative enthalpies of the perovskite structures.","abstract_html":"This thesis makes contributions to the methodology of quantitative description of the tilting systems of perovskite structures and theoretical analysis of high-pressure phase transitions of representative perovskites. Chapter 1 and 2 introduce the perovskite structures, tilting classification and descriptions. The structures in each of the 15 tilt systems have been decomposed in to the amplitudes of symmetry-adapted modes in order to provide a clear and unambiguous definition of the tilt angles. A general expression in terms of tilt angles for the ratio of the volumes of the two polyhedra within the perovskite structure is derived. Chapter 3 uses the first-principles plane-wave pseudopotential calculations to investigate the high-pressure to phase transition and elasticity of LaAlO3 perovskite. This second order transition is determined to occur at ~14 GPa by the pressure variation of the squared frequency of the soft R-point mode in the structure. Elastic moduli are inverted from the calculated stress-strain data by the singular value decomposition method. The Landau parameters for this phase transition are calibrated from the calculation results. Chapter 4 uses the same method to investigate the high-pressure phase transitions and elasticity of YAlO3 perovskite. The Pnma, Imma, I4/mcm, , perovskite structures and the NH4CdCl3-, Gd2S3-, U2S3-, CaIrO3-type structures are considered. A continuous Pnma to Imma transition occurs at ~89 GPa, determined from the soft Z-point mode of the Imma structure. Then, a discontinuous Imma to I4/mcm transition occurs at ~100 GPa, suggested by the relative enthalpies and phonon dispersions. The elasticities of the Pnma, Imma and I4/mcm structures show mechanical stabilities compatible with the phase transitions. The NH4CdCl3- and CaIrO3-type structures are dynamically stable although not energetically favorable. The relative A/B site polyhedral volume ratios are found to qualitatively reproduce the relative enthalpies of the perovskite structures.","abstract_has_math":false,"creators":["Wang, Di"],"institution":"Virginia Tech","degree_name":"Ph. D.","degree_level":"doctoral","degree_discipline":"Geosciences","degree_department":"Geosciences","school":null,"contributors":[],"advisors":[],"committee_chairs":["Ross, Nancy L."],"committee_members":["Wentzcovitch, Renata M.","Angel, Ross J.","Gibbs, Gerald V.","King, Scott D."],"year":2012,"date_issued":"2012-04-26","date_published":"2012-04-26","updated_at":"2026-07-22T22:19:26Z","subjects":["DFT","YAlO3","LaAlO3","phonon","elasticity","phase transition","high pressure","symmetry-adapted mode","perovskite"],"languages":[],"rights":["In Copyright"],"rights_urls":["http://rightsstatements.org/vocab/InC/1.0/"],"identifier_entries":[{"key":"dc:identifier.other","label":"Dc Identifier Other","values":["etd-05082012-144621"],"render_values":[{"text":"etd-05082012-144621","href":null,"code":true}]}]},"links":{"outbound_url":"http://hdl.handle.net/10919/37733","outbound_label":"Handle","outbound_source":"dc:identifier.uri"},"metadata_groups":[{"id":"people","label":"People","entries":[{"key":"dc:contributor.committeechair","label":"Committee Chair","values":["Ross, Nancy L."]},{"key":"dc:contributor.committeemember","label":"Committee Member","values":["Wentzcovitch, Renata M.","Angel, Ross J.","Gibbs, Gerald V.","King, Scott D."]},{"key":"dc:contributor.department","label":"Department","values":["Geosciences"]},{"key":"dc:creator","label":"Author","values":["Wang, Di"]}]},{"id":"academic_context","label":"Academic Context","entries":[{"key":"dc:date.accessioned","label":"Dc Date Accessioned","values":["2014-03-14T21:10:49Z"]},{"key":"dc:date.available","label":"Dc Date Available","values":["2014-03-14T21:10:49Z","2012-06-06"]},{"key":"dc:date.issued","label":"Date","values":["2012-04-26"]},{"key":"dc:publisher","label":"Institution","values":["Virginia Tech"]},{"key":"dc:type","label":"Dc Type","values":["Dissertation"]},{"key":"thesis:degree_discipline","label":"Discipline","values":["Geosciences"]},{"key":"thesis:degree_level","label":"Degree Level","values":["doctoral"]},{"key":"thesis:degree_name","label":"Degree Name","values":["Ph. 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Chapter 1 and 2 introduce the perovskite structures, tilting classification and descriptions. The structures in each of the 15 tilt systems have been decomposed in to the amplitudes of symmetry-adapted modes in order to provide a clear and unambiguous definition of the tilt angles. A general expression in terms of tilt angles for the ratio of the volumes of the two polyhedra within the perovskite structure is derived. Chapter 3 uses the first-principles plane-wave pseudopotential calculations to investigate the high-pressure to phase transition and elasticity of LaAlO3 perovskite. This second order transition is determined to occur at ~14 GPa by the pressure variation of the squared frequency of the soft R-point mode in the structure. Elastic moduli are inverted from the calculated stress-strain data by the singular value decomposition method. The Landau parameters for this phase transition are calibrated from the calculation results. Chapter 4 uses the same method to investigate the high-pressure phase transitions and elasticity of YAlO3 perovskite. The Pnma, Imma, I4/mcm, , perovskite structures and the NH4CdCl3-, Gd2S3-, U2S3-, CaIrO3-type structures are considered. A continuous Pnma to Imma transition occurs at ~89 GPa, determined from the soft Z-point mode of the Imma structure. Then, a discontinuous Imma to I4/mcm transition occurs at ~100 GPa, suggested by the relative enthalpies and phonon dispersions. The elasticities of the Pnma, Imma and I4/mcm structures show mechanical stabilities compatible with the phase transitions. The NH4CdCl3- and CaIrO3-type structures are dynamically stable although not energetically favorable. The relative A/B site polyhedral volume ratios are found to qualitatively reproduce the relative enthalpies of the perovskite structures."]},{"key":"dc:description.degree","label":"Dc Description Degree","values":["Ph. D."]},{"key":"dc:title","label":"Title","values":["Some Aspects of the Crystal Chemistry of Perovskites under High Pressures"]}]}],"canonical_facts":{"dc:contributor.committeechair":["Ross, Nancy L."],"dc:contributor.committeemember":["Wentzcovitch, Renata M.","Angel, Ross J.","Gibbs, Gerald V.","King, Scott D."],"dc:contributor.department":["Geosciences"],"dc:creator":["Wang, Di"],"dc:date.accessioned":["2014-03-14T21:10:49Z"],"dc:date.available":["2014-03-14T21:10:49Z","2012-06-06"],"dc:date.issued":["2012-04-26"],"dc:description.abstract":["This thesis makes contributions to the methodology of quantitative description of the tilting systems of perovskite structures and theoretical analysis of high-pressure phase transitions of representative perovskites. Chapter 1 and 2 introduce the perovskite structures, tilting classification and descriptions. The structures in each of the 15 tilt systems have been decomposed in to the amplitudes of symmetry-adapted modes in order to provide a clear and unambiguous definition of the tilt angles. A general expression in terms of tilt angles for the ratio of the volumes of the two polyhedra within the perovskite structure is derived. Chapter 3 uses the first-principles plane-wave pseudopotential calculations to investigate the high-pressure to phase transition and elasticity of LaAlO3 perovskite. This second order transition is determined to occur at ~14 GPa by the pressure variation of the squared frequency of the soft R-point mode in the structure. Elastic moduli are inverted from the calculated stress-strain data by the singular value decomposition method. The Landau parameters for this phase transition are calibrated from the calculation results. Chapter 4 uses the same method to investigate the high-pressure phase transitions and elasticity of YAlO3 perovskite. The Pnma, Imma, I4/mcm, , perovskite structures and the NH4CdCl3-, Gd2S3-, U2S3-, CaIrO3-type structures are considered. A continuous Pnma to Imma transition occurs at ~89 GPa, determined from the soft Z-point mode of the Imma structure. Then, a discontinuous Imma to I4/mcm transition occurs at ~100 GPa, suggested by the relative enthalpies and phonon dispersions. The elasticities of the Pnma, Imma and I4/mcm structures show mechanical stabilities compatible with the phase transitions. The NH4CdCl3- and CaIrO3-type structures are dynamically stable although not energetically favorable. The relative A/B site polyhedral volume ratios are found to qualitatively reproduce the relative enthalpies of the perovskite structures."],"dc:description.degree":["Ph. D."],"dc:identifier.other":["etd-05082012-144621"],"dc:identifier.uri":["http://hdl.handle.net/10919/37733"],"dc:publisher":["Virginia Tech"],"dc:rights":["In Copyright"],"dc:rights.uri":["http://rightsstatements.org/vocab/InC/1.0/"],"dc:subject":["DFT","YAlO3","LaAlO3","phonon","elasticity","phase transition","high pressure","symmetry-adapted mode","perovskite"],"dc:title":["Some Aspects of the Crystal Chemistry of Perovskites under High Pressures"],"dc:type":["Dissertation"],"thesis:degree_discipline":["Geosciences"],"thesis:degree_level":["doctoral"],"thesis:degree_name":["Ph. D."],"thesis:institution_name":["Virginia Polytechnic Institute and State University"]},"updated_at":"2026-07-22T22:19:26Z"}