Browsing by Author "Chaturvedi, Vipul"
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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 Doping- and Strain-Dependent Electrolyte-Gate-Induced Perovskite to Brownmillerite Transformation in Epitaxial La1−xSrxCoO3−δ Films(2021-11-17) Chaturvedi, Vipul; Postiglione, William M; Chakraborty, Rohan D; Yu, Biqiong; Tabiś, Wojciech; Hameed, Sajna; Biniskos, Nikolaos; Jacobson, Andrew; Zhang, Zhan; Zhou, Hua; Greven, Martin; Ferry, Vivian E; Leighton, Chris; leighton@umn.edu; Leighton, Chris; Chemical Engineering and Materials Science, University of Minnesota; AGH University of Science and Technology, Faculty of Physics and Applied Computer Science; Advanced Photon Source, Argonne National Laboratory; School of Physics and Astronomy, University of MinnesotaElectrolyte-gate-induced perovskite to brownmillerite transformations in La1-xSrxCoO3-d (LSCO) has been shown to be a facile technique to toggle between disparate electronic and magnetic phases in a single perovskite oxide thin film. Here we study the doping (Sr concentration), and strain (epitaxially imparted from the substrate) dependence of this topotactic transformation in LSCO thin films across almost the entire phase diagram. This repository page serves as a place to store the Figure plots and raw data from the cited publication.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 Strain- and Electrolyte-Gating-Based Control of Magnetism in Cobaltite Thin Films(2021-11) Chaturvedi, VipulTransition metal based perovskite oxides with the common chemical formula ABO3 exhibit diverse physical properties of fundamental and technological importance. Among these, perovskite cobaltites (where B = Co) have long been understood to display intriguing phenomena known as spin-state crossovers or transitions, where the spin of the cobalt ion changes versus temperature, pressure, etc. Recent advances in synthesizing thin films of these cobaltites have attracted significant attention and have led to realization of novel magnetic ground states not observable in bulk samples. Employing heteroepitaxial strain and electric-field effects, this thesis is aimed at understanding and controlling the emergent magnetic ground states that arise in two prototypical cobaltite thin film systems: La1-xSrxCoO3-δ and (Pr1-yYy)1-xCaxCoO3-δ, addressing several pressing open questions related to these material systems, providing avenues for several potential applications including resistive switching devices, neuromorphic computing, switchable magnetic, and photonic devices etc. Starting with LaCoO3-δ films, we first address open questions concerning electronic transport properties and correlations with the strain-stabilized ferromagnetic state under tensile strain. Detailed magnetotransport measurements reveal a striking inversion of the majority carrier type under tensile strain, from the p-type seen in bulk and under compression, to n-type under tension. We interpret these results in terms of a tensile-strain-induced redistribution of orbital occupancies towards eg states, in concert with substantial lowering of the electron effective mass. While thus far overlooked, we thus report that ferromagnetism in epitaxial LaCoO3-δ films is thus directly correlated with n-type behavior, providing important insight into the perplexing ferromagnetic state in this system. Moving on to (Pr0.85Y0.15)0.3Ca0.7CoO3-δ films, using large compressive heteroepitaxial strain, we report realization of a first-order valence-driven spin-state/metal-insulator transitions to at least 245 K (from 135 K in bulk), potentially within reach of room temperature. The obvious technological implications of this result are accompanied by new fundamental prospects also, as we additionally establish complete strain control of the electronic ground state, from a ferromagnetic metallic state under tension to nonmagnetic and insulating under compression, thereby exposing a novel potential quantum critical point. Finally, using electrolyte gating techniques, we present the first study of the voltage-induced topotactic perovskite to brownmillerite transformation across almost the entire phase diagram of ion-gel-gated La1-xSrxCoO3- (0 x 0.70), employing epitaxial films on three different substrates to understand the impact of strain. Electronic transport and operando synchrotron X-ray diffraction confirm that the perovskite to brownmillerite transformation can be driven at essentially all x, including, critically, x 0.50, where the perovskite phase is highly stable. Importantly, the threshold voltage for the transformation is tunable (between 3 V and 0 V) via Sr doping and strain, of interest for device applications. The decreasing threshold voltage with doping and strain are interpreted in terms of trends in oxygen vacancy formation enthalpy (not diffusivity), highlighting the essential role of thermodynamics (over kinetics), driven by the instability of formal Co4+ in these compounds. These findings substantially advance the practical and mechanistic understanding of this voltage-driven transformation, with fundamental and technological implications. Overall, this thesis demonstrates the power of heteroepitaxial strain and electric-field effects in developing fundamental understanding as well as control of magnetism in cobaltite thin films, highlighting abundant technological potential in these materials.Item Supporting data for Wide-range continuous tuning of the thermal conductivity of La0.5Sr0.5CoO3−δ films via room-temperature ion-gel gating(2023-04-19) Zhang, Yingying; Postiglione, William M; Xie, Rui; Zhang, Chi; Zhou, Hao; Chaturvedi, Vipul; Heltemes, Kei; Zhou, Hua; Feng, Tianli; Leighton, Chris; Wang, Xiaojia; wang4940@umn.edu; Wang, Xiaojia; Materials Research Science & Engineering CenterThese files contain data along with associated output from instrumentation supporting all results reported in Wide-range continuous tuning of the thermal conductivity of La0.5Sr0.5CoO3-delta films via room-temperature ion-gel gating. Solid-state control of the thermal conductivity of materials is of exceptional interest for novel devices such as thermal diodes and switches. Here, we demonstrate the ability to continuously tune the thermal conductivity of nanoscale films of La0.5Sr0.5CoO3-delta (LSCO) by a factor of over 5, via a room-temperature electrolyte-gate-induced non-volatile topotactic phase transformation from perovskite (with ≈ 0.1) to an oxygen-vacancy-ordered brownmillerite phase (with = 0.5), accompanied by a metal-insulator transition. Combining time-domain thermoreflectance and electronic transport measurements, model analyses based on molecular dynamics and Boltzmann transport, and structural characterization by X-ray diffraction, we uncover and deconvolve the effects of these transitions on heat carriers, including electrons and lattice vibrations. The wide-range continuous tunability of LSCO thermal conductivity enabled by low-voltage (below 4 V) room-temperature electrolyte gating opens the door to non-volatile dynamic control of thermal transport in perovskite-based functional materials, for thermal regulation and management in device applications. Authors to whom correspondence should be addressed are Chris Leighton (leighton@umn.edu) and Xiaojia Wang (wang4940@umn.edu).