Browsing by Author "Birol, Turan"
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Item Chemical bonding and Born charge in 1T-HfS2(2021-04-09) Neal, Sabine N; Li, Shutong; Birol, Turan; Musfeldt, Janice L; li000269@umn.edu; Li, ShutongWe combine infrared absorption and Raman scattering spectroscopies to explore the properties of 1T-HfS2- a heavy transition metal chalcogenide with strong spin-orbit coupling due to incorporation of the 5d center. We employ the LO-TO splitting of the Eu mode along with a reevaluation of mode mass, unit cell volume, and dielectric constant to reveal the Born effective charge. We find ZB*= 5.33e, in excellent agreement with complementary first principles calculations. In addition to resolving controversy over the nature of chemical bonding in this system, we decompose the Born charge into polarizability and local (ionic) charge. We find α= 5.07 Å3 and Z*= 5.19e, respectively. In order to understand how ZB* relates to the nominal 4+ charge of the Hf center, we decompose the theoretical Born effective charge into band-by-band contributions, and find that polar displacement-induced charge transfer from sulfur p to hafnium d orbitals is responsible for the enhancement of Born charge. 1T-HfS2 is thus an ionic crystal with strong and dynamic covalent effects.Item Data files of work on LaCoO3 using VASP(2020-08-05) Paul, Arpita; Birol, Turan; paula@umn.edu; Paul, Arpita; Birol Research GroupSample VASP input file used to study LaCoO3 (INCAR) Band structures of LaCoO3 at each values of strain (used to determine carrier effective mass) Wannier functions derived from e_g orbitals of LaCoO3 (used to determine splitting between dx2-y2 and dz2 orbitals)Item Data for Crystal-Chemical Origins of the Ultrahigh Conductivity of Metallic Delafossites(2023-11-09) Zhang, Yi; Tutt, Fred; Evans, Guy N; Sharma, Prachi; Haugstad, Greg; Kaiser, Ben; Ramberger, Justin; Bayliff, Samuel; Tao, Yu; Manno, Mike; Garcia-Barriocanal, Javier; Chaturvedi, Vipul; Fernandes, Rafael M; Birol, Turan; Seyfried Jr, William E; Leighton, Chris; leighton@umn.edu; Leighton, Chris; Leighton Electronic and Magnetic Materials LabDespite their highly anisotropic complex-oxidic nature, certain delafossite compounds (e.g., PdCoO2, PtCoO2) are the most conductive oxides known, for reasons that remain poorly understood. Their room-temperature conductivity can exceed that of Au, while their low-temperature electronic mean-free-paths reach an astonishing 20 um. It is widely accepted that these materials must be ultrapure to achieve this, although the methods for their growth (which produce only small crystals) are not typically capable of such. Here, we first report a new approach to PdCoO2 crystal growth, using chemical vapor transport methods to achieve order-of-magnitude gains in size, the highest structural qualities yet reported, and record residual resistivity ratios (>440). Nevertheless, the first detailed mass spectrometry measurements on these materials reveal that they are not ultrapure, typically harboring 100s-of-parts-per-million impurity levels. Through quantitative crystal-chemical analyses, we resolve this apparent dichotomy, showing that the vast majority of impurities are forced to reside in the Co-O octahedral layers, leaving the conductive Pd sheets highly pure (~1 ppm impurity concentrations). These purities are shown to be in quantitative agreement with measured residual resistivities. We thus conclude that a previously unconsidered “sublattice purification” mechanism is essential to the ultrahigh low-temperature conductivity and mean-free-path of metallic delafossites. This dataset contains all digital data in the published paper of the same name.Item Data for Non-Local Spin Transport in the Light Intermetallic Alloy Al2Cu(2024-10-24) Ramberger, Justin; Kaiser, Ben; Dutta, Paromita; Norum, Mikaela; Birol, Turan; Leighton, Chris; leighton@umn.edu; Leighton, Chris; Leighton Research GroupData prove the existence of the phase via x-ray diffraction, energy-dispersive x-ray spectroscopy, and electronic transport. The material is then evaluated with regard to spin transport through the use of non-local spin valves (NLSVs). The provided data can be used to determine the Elliot-Yafet parameters for defects and phonons that describe spin relaxation in this metal.Item Data for Reexamination of the electronic phase diagram of doped NiS₂: Electronic, magnetic, and structural inhomogeneity across the Mott insulator-metal transition(2024-11-04) Tao, Yu; Das, Bhaskar; Calder, Stuart; Day-Roberts, Ezra; Maiti, Moumita; Lee, Yeon; Komar, Caitlyn; Birol, Turan; Leighton, Chris; leighton@umn.edu; Leighton, Chris; Leighton Electronic and Magnetic Materials Lab; Chemical Engineering and Materials Science, University of MinnesotaPyrite-structure NiS₂ is, in principle, a model antiferromagnetic Mott insulator that can be electron doped, hole doped, and bandwidth controlled. Despite decades of study, however, the electronic and magnetic behavior of NiS₂ have proven challenging to understand. Here, we build on recent advances establishing surface conduction in NiS₂ to completely reexamine the electronic phase behavior of electron- and hole-doped single-crystal Ni₁₋ₓCuₓS₂ and Ni₁₋ₓCoₓS₂. Magnetometry, heat capacity, neutron diffraction, and electronic transport measurements suggest that prior work missed vital details of the magnetic ordering in this system. While electron and hole doping rapidly increase the antiferromagnetic ordering temperature (by as much as 4-fold by x ≈ 0.1), signatures remain of antiferromagnetic and weak ferromagnetic ordering at the same temperatures as in undoped NiS₂. As these undoped ordering temperatures remain constant, the associated magnetic moments are diminished by doping, strongly implicating electronic/ magnetic phase coexistence across the Mott insulator-metal transition. Substantial structural changes and inhomogeneity accompany these evolutions, highlighting the importance of structural-chemical-electronic-magnetic coupling in NiS₂. The insulator-metal transition is also strongly electron/hole asymmetric, which we interpret with the aid of complementary dynamical mean-field theory results. These findings significantly revise and advance our understanding of the electronic phase behavior of this prototypical Mott insulator, highlighting the essential role of electronic, magnetic, structural, and chemical inhomogeneity across the Mott transition. This dataset contains all digital data in the published paper of the same name.Item Data for Room-Temperature Valence Transition in a Strain-Tuned Perovskite Oxide(2022-11-09) Chaturvedi, Vipul; Ghosh, Supriya; Gautreau, Dominique; Postiglione, William M; Dewey, John E; Quarterman, Patrick; Balakrishnan, Purnima P; Kirby, Brian J; Zhou, Hua; Cheng, Huikai; Huon, Amanda; Fitzsimmons, Michael R; Korostynski, Caroline; Jacobson, Andrew; Figari, Lucca; Barriocanal, Javier G; Birol, Turan; Mkhoyan, K Andre; Leighton, Chris; leighton@umn.edu; Leighton, Chris; Leighton Electronic and Magnetic Materials LabCobalt oxides have long been understood to display intriguing phenomena known as spin-state crossovers, where the cobalt ion spin changes vs. temperature, pressure, etc. A very different situation was recently uncovered in praseodymium-containing cobalt oxides, where a first-order coupled spin-state/structural/metal-insulator transition occurs, driven by a remarkable praseodymium valence transition. Such valence transitions, particularly when triggering spin-state and metal-insulator transitions, offer highly appealing functionality, but have thus far been confined to cryogenic temperatures in bulk materials (e.g., 90 K in Pr1-xCaxCoO3). Here, we show that in thin films of the complex perovskite (Pr1-yYy)1-xCaxCoO3-delta, heteroepitaxial strain tuning enables stabilization of valence-driven spin-state/structural/metal-insulator transitions to at least 291 K, i.e., around room temperature. This dataset contains all digital data published in the Nature Communications paper of the same name.Item Dopant segregation inside and outside dislocation cores in perovskite BaSnO 3 and reconstruction of the local atomic and electronic structures(2021-04-26) Yun, Hwanhui; Prakash, Abhinav; Birol, Turan; Jalan, Bharat; Mkhoyan, K. Andre; yunxx133@umn.edu; Yun, HwanhuiDistinct dopant behaviors inside and outside dislocation cores are identified by atomic-resolution electron microscopy in perovskite BaSnO3 with considerable consequences on local atomic and electronic structures. Driven by elastic strain, when A-site designated La dopants segregate near a dislocation core, the dopant atoms accumulate at the Ba sites in compressively strained regions. This triggers formation of Ba-vacancies adjacent to the core atomic sites resulting in reconstruction of the core. Notwithstanding the presence of extremely large tensile strain fields, when La atoms segregate inside the dislocation core, they become B-site dopants, replacing Sn atoms and compensating the positive charge of the core oxygen vacancies. Electron energy-loss spectroscopy shows that the local electronic structure of these dislocations changes dramatically due to segregation of the dopants inside and around the core ranging from formation of strong La-O hybridized electronic states near the conduction band minimum to insulator-to-metal transition.Item Raman spectroscopy data and phonon calculations for ScV6Sn6 in P6/mmm and R-3m structures, 2023(2023-06-27) Ritz, Ethan T; Birol, Turan; Gu, Yanhong; Musfeldt, Janice L; eritz@umn.edu; Ritz, Ethan T; Birol Research Group, University of Minnesota; Musfeldt Group, University of Tennessee KnoxvilleWe use density functional theory (DFT) to calculate the phonon frequencies and the distortions associated with them in the compound ScV6Sn6 in the P6/mmm and R-3m space groups, then compute the overlap between the Raman-active phonons in each structure. This data includes scripts to generate the DFT submission files, the results of those simulations, as well as MATLAB scripts to plot the results. We also include experimental Raman spectroscopy data at temperatures from 5.5 K to 300 K.Item Simulation data from: Free carrier induced ferroelectricity in layered perovskites(2021-06-08) Li, Shutong; Birol, Turan; li000269@umn.edu; Li, ShutongDoping ferroelectrics with carriers is often detrimental to polarization. This makes the design and discovery of metals that undergo a ferroelectric-like transition challenging. In this letter, we show from first principles that the oxygen octahedral rotations in perovskites are often enhanced by electron doping, and this can be used as a means to strengthen the structural polarization in certain hybrid-improper ferroelectrics -- compounds in which the polarization is not stabilized by the long range Coulomb interactions but is instead induced by a trilinear coupling to octahedral rotations. We use this design strategy to predict a cation ordered Ruddlesden-Popper compound that can be driven into a metallic ferroelectric-like phase via electrolyte gating.Item Strain effect on the ground-state crystal structure of Sr2SnO4 Ruddlesden-Popper oxides(2022-09-08) Yun, Hwanhui; Gautreau, Dominique; Mkhoyan, K. Andre; Birol, Turan; yunxx133@umn.edu; Yun, Hwanhui; Theoretical Materials Physics GroupSimulation data for a manuscript 'Strain effect on the ground-state structure of Sr2SnO4 Ruddlesden-Popper oxides'. Key data including structures and input files for structural relaxation and phonon calculation of various phases in Sr2SnO4 are included.Item Supporting data for Metallic line defect in wide-bandgap transparent perovskite BaSnO₃(2021-01-22) Yun, Hwanhui; Topsakal, Mehmet; Prakash, Abhinav; Jalan, Bharat; Jong Seok, Jeong; Birol, Turan; Mkhoyan, K Andre; yunxx133@umn.edu; Yun, HwanhuiA line defect with metallic characteristics has been found in optically transparent BaSnO₃ perovskite thin films. The distinct atomic structure of the defect core, composed of Sn and O atoms, was visualized by atomic-resolution scanning transmission electron microscopy (STEM). When doped with La, dopants that replace Ba atoms preferentially segregate to specific crystallographic sites adjacent to the line defect. The electronic structure of the line defect probed in STEM with electron energy-loss spectroscopy was supported by ab initio theory, which indicates the presence of Fermi level–crossing electronic bands that originate from defect core atoms. These metallic line defects also act as electron sinks attracting additional negative charges in these wide-bandgap BaSnO₃ films.Item Suppressing The Ferroelectric Switching Barrier in Hybrid Improper Ferroelectrics(2020-08-26) Birol, Turan; Li, Shutong; tbirol@umn.edu; Birol, TuranIntegration of ferroelectric materials in novel technological applications requires low coercive field materials, and consequently, design strategies to reduce the ferroelectric switching barriers. In this first principles study, we show that biaxial strain, which has a strong e ect on the ferroelectric ground states, can also be used to tune the switching barrier of hybrid improper ferroelectric Ruddlesden-Popper oxides. We identify the region of the strain-tolerance factor phase diagram where this intrinsic barrier is suppressed, and show that it can be explained in relation to strain induced phase transitions to nonpolar phases.