Charting the complete elastic properties of inorganic crystalline compounds

The elastic constant tensor of an inorganic compound provides a complete description of the response of the material to external stresses in the elastic limit. It thus provides fundamental insight into the nature of the bonding in the material, and it is known to correlate with many mechanical properties. Despite the importance of the elastic constant tensor, it has been measured for a very small fraction of all known inorganic compounds, a situation that limits the ability of materials scientists to develop new materials with targeted mechanical responses. To address this deficiency, we present here the largest database of calculated elastic properties for inorganic compounds to date. The database currently contains full elastic information for 1,181 inorganic compounds, and this number is growing steadily. The methods used to develop the database are described, as are results of tests that establish the accuracy of the data. In addition, we document the database format and describe the different ways it can be accessed and analyzed in efforts related to materials discovery and design

First-Principles Modeling of Thin-Film Ferroelectrics

The goal of this dissertation is to explore the properties of thin-film ferroelectrics using first-principles computational methods. Achieving this goal requires both the development of efficient methods for computing thin-film properties as well as the application of these methods to a variety of thin-film materials of interest. The research included in this dissertation is thus composed of a mix of these two efforts.First, the structural properties, energetics, and polarizations of perovskite-based thin-film oxide systems are computed as a function of biaxial strain state and epitaxial orientation, employing an automated computational workflow based on density functional theory (DFT). A total of 14 compositions are considered, of the form ABO3, with A=Ba, K, Na, Pb, and Sr and non-magnetic B=Hf, Sn, Ti, Zr, Nb, Ta, and V site cations chosen to yield tolerance factors with values ranging between 0.95 and 1.1. Three biaxial strain states corresponding to epitaxial growth of (100)-, (110)-, and (111)-oriented films are considered, with misfit strains ranging between -4% to 4%. Results are presented for the series of perovskite-derived phases, and their corresponding symmetries, which are energetically favorable as a function of misfit strain, along with their corresponding equilibrium atomic positions, lattice parameters, and electric polarizations. The results demonstrate robust trends of in-plane polarization enhancement under tensile strain for all epitaxial orientations, and out-of-plane polarization enhancement with compression for the (100)- and (110)-oriented films. Strains corresponding to the (111)-growth orientation lead to a wider variety of out-of-plane polarization behavior, with BaTiO3 showing anomalous diminishing polarization with compression. Epitaxial orientation is shown to have a strong effect on the nature of strain-induced phase transitions, with (100)-oriented systems tending to have smooth, second-order transitions and (110)- and (111)-oriented systems more commonly exhibiting first-order transitions. The significance of this effect for device applications is discussed, and a number of systems are identified as potentially interesting for ferroelectric thin-film applications based on energetic stability and polarization behavior. Analysis of polarization behavior across different orientations reveals distinct groups into which compositions can be organized, some of which having polarization dependencies on misfit strain that have not been predicted previously.Following the work described above, ground-state epitaxial phase diagrams are calculated by DFT for SrTiO3, CaTiO3, and SrHfO3 perovskite-based compounds, accounting for effects of antiferrodistortive and A-site displacement modes. Biaxial strain states corresponding to epitaxial growth of (001)-oriented films are considered, with misfit strains ranging between -4% and 4%. Ground-state structures are determined using a computational procedure in which input structures for DFT optimizations are identified as local minima in expansions of the total energy with respect to strain and soft-mode degrees of freedom. Comparison to results of previous DFT studies demonstrates the effectiveness of the computational approach in predicting ground-state phases. The calculated results show that antiferrodistortive octahedral rotations and associated A-site displacement modes act to suppress polarization and reduce epitaxial strain energy. A projection of calculated atomic displacements in the ground-state epitaxial structures onto soft-mode eigenvectors shows that three ferroelectric and six antiferrodistortive displacement modes are dominant at all misfit strains considered, with the relative contributions from each varying systematically with strain. Additional A-site displacement modes contribute to the atomic displacements in CaTiO3 and SrHfO3, which serve to optimize the coordination of the undersized A-site cation.Further, an effort is made to identify alternative vanadate perovskite-derivative systems similar to the well-studied pressure-stabilized PVO structure. To achieve this, the stability of perovskite-derivative thin-film structures of KVO3 and NaVO3 are studied under compressive biaxial strain. The electronic structure and polar properties of these compounds are computed as a function of biaxial strain, and the results are compared to those obtained for experimentally-observed PbVO3 structures. It is demonstrated that the substitution of Pb with monovalent K or Na cations increases the strength of the vanadyl bond due to the removal of the spatially extended Pb 6p states. Both KVO3 and NaVO3 exhibit epitaxially stabilized perovskite-derivative phases having large polarizations and low misfit strain energies. The calculated epitaxial phase diagram for KVO3 predicts a strain-induced phase separation from -4% to 1.5% misfit strain into a ferroelectric $Cm$ phase, having square-pyramidal coordination of the B-site, and a paraelectric Pbcm phase, having tetrahedral coordination of the B-site. The results show that strain-stabilized polar vanadate compounds may occur for other compositions in addition to PVO, and that changes in the A-site species can be used to tune bonding, structure, and functional properties in these systems

First-Principles Modeling of Thin-Film Ferroelectrics

The goal of this dissertation is to explore the properties of thin-film ferroelectrics using first-principles computational methods. Achieving this goal requires both the development of efficient methods for computing thin-film properties as well as the application of these methods to a variety of thin-film materials of interest. The research included in this dissertation is thus composed of a mix of these two efforts.First, the structural properties, energetics, and polarizations of perovskite-based thin-film oxide systems are computed as a function of biaxial strain state and epitaxial orientation, employing an automated computational workflow based on density functional theory (DFT). A total of 14 compositions are considered, of the form ABO3, with A=Ba, K, Na, Pb, and Sr and non-magnetic B=Hf, Sn, Ti, Zr, Nb, Ta, and V site cations chosen to yield tolerance factors with values ranging between 0.95 and 1.1. Three biaxial strain states corresponding to epitaxial growth of (100)-, (110)-, and (111)-oriented films are considered, with misfit strains ranging between -4% to 4%. Results are presented for the series of perovskite-derived phases, and their corresponding symmetries, which are energetically favorable as a function of misfit strain, along with their corresponding equilibrium atomic positions, lattice parameters, and electric polarizations. The results demonstrate robust trends of in-plane polarization enhancement under tensile strain for all epitaxial orientations, and out-of-plane polarization enhancement with compression for the (100)- and (110)-oriented films. Strains corresponding to the (111)-growth orientation lead to a wider variety of out-of-plane polarization behavior, with BaTiO3 showing anomalous diminishing polarization with compression. Epitaxial orientation is shown to have a strong effect on the nature of strain-induced phase transitions, with (100)-oriented systems tending to have smooth, second-order transitions and (110)- and (111)-oriented systems more commonly exhibiting first-order transitions. The significance of this effect for device applications is discussed, and a number of systems are identified as potentially interesting for ferroelectric thin-film applications based on energetic stability and polarization behavior. Analysis of polarization behavior across different orientations reveals distinct groups into which compositions can be organized, some of which having polarization dependencies on misfit strain that have not been predicted previously.Following the work described above, ground-state epitaxial phase diagrams are calculated by DFT for SrTiO3, CaTiO3, and SrHfO3 perovskite-based compounds, accounting for effects of antiferrodistortive and A-site displacement modes. Biaxial strain states corresponding to epitaxial growth of (001)-oriented films are considered, with misfit strains ranging between -4% and 4%. Ground-state structures are determined using a computational procedure in which input structures for DFT optimizations are identified as local minima in expansions of the total energy with respect to strain and soft-mode degrees of freedom. Comparison to results of previous DFT studies demonstrates the effectiveness of the computational approach in predicting ground-state phases. The calculated results show that antiferrodistortive octahedral rotations and associated A-site displacement modes act to suppress polarization and reduce epitaxial strain energy. A projection of calculated atomic displacements in the ground-state epitaxial structures onto soft-mode eigenvectors shows that three ferroelectric and six antiferrodistortive displacement modes are dominant at all misfit strains considered, with the relative contributions from each varying systematically with strain. Additional A-site displacement modes contribute to the atomic displacements in CaTiO3 and SrHfO3, which serve to optimize the coordination of the undersized A-site cation.Further, an effort is made to identify alternative vanadate perovskite-derivative systems similar to the well-studied pressure-stabilized PVO structure. To achieve this, the stability of perovskite-derivative thin-film structures of KVO3 and NaVO3 are studied under compressive biaxial strain. The electronic structure and polar properties of these compounds are computed as a function of biaxial strain, and the results are compared to those obtained for experimentally-observed PbVO3 structures. It is demonstrated that the substitution of Pb with monovalent K or Na cations increases the strength of the vanadyl bond due to the removal of the spatially extended Pb 6p states. Both KVO3 and NaVO3 exhibit epitaxially stabilized perovskite-derivative phases having large polarizations and low misfit strain energies. The calculated epitaxial phase diagram for KVO3 predicts a strain-induced phase separation from -4% to 1.5% misfit strain into a ferroelectric $Cm$ phase, having square-pyramidal coordination of the B-site, and a paraelectric Pbcm phase, having tetrahedral coordination of the B-site. The results show that strain-stabilized polar vanadate compounds may occur for other compositions in addition to PVO, and that changes in the A-site species can be used to tune bonding, structure, and functional properties in these systems

Healthy Writing, Unhealthy Writer: An Anomalous Autoethnography

(Statement of Responsibility) by Harrison Angsten(Thesis) Thesis (B.A.) -- New College of Florida, 2022RESTRICTED TO NCF STUDENTS, STAFF, FACULTY, AND ON-CAMPUS USE(Bibliography) Includes bibliographical references.This bibliographic record is available under the Creative Commons CC0 public domain dedication. The New College of Florida Libraries, as creator of this bibliographic record, has waived all rights to it worldwide under copyright law, including all related and neighboring rights, to the extent allowed by law.Faculty Sponsor: Noble, Christophe

Evaluating Severity Differences of Depression and Anxiety in Self-Report and Clinician-Rated Measures

Depression and anxiety are core components of the most commonly diagnosed behavioral health disorders. While they are two separate constructs, they contain many overlapping symptoms and are often diagnosed co-morbidly. Many studies have been conducted to test different models of depression, anxiety, and their comorbidity. Another important variable to focus on, however, is how depression and anxiety are assessed. Self-report and clinician-rated measures are two standard ways in which these constructs are assessed. This study sought to address issues related to the reliability and validity of two specific assessment methods for depression and anxiety. The Beck Depression Inventory-II (BDI-II) and the Beck Anxiety Inventory (BAI) were used as the self-report measures, while the Hamilton Depression Rating Scale (HDRS) and the Hamilton Anxiety Rating Scale (HARS) were used as the clinician-rated measures. It was found that the BDI-II and HDRS, and the BAI and HARS were highly correlated. However, the study found that percent agreement between classification categories of the BDI-II and HDRS, and the BAI and HARS only occurred approximately 60% of the time. Decisions are made about treatment and medication based on the classification categories of these instruments. If these types of results occur in future studies, diagnostically-relevant instruments may need to be adjusted in order to exhibit a stronger relationship between correlations and classification categories

A Pyschological Experiment: An Analysis of the Belgium Film, Jeanne Dielman, 23 quai du Commerce, 1080 Bruxelles

In this essay, I discuss how filmaker Chantal Akerman sets up Jeanne Dielman as a means to study the psychology nature of the titular character through the course of three full days in her life. By doing so, Akerman allows us to break down this mental make up as it subtley shifts throughout the film leading up to its dramatic climax and resolution