Temperature and thickness evolution and epitaxial breakdown in highly-strained BiFeO3 thin films

We present the temperature- and thickness-dependent structural and morphological evolution of strain induced transformations in highly-strained epitaxial BiFeO3 films deposited on LaAlO3 (001) substrates. Using high-resolution X-ray diffraction and temperature-dependent scanning-probe-based studies we observe a complex temperature- and thickness-dependent evolution of phases in this system. A thickness-dependent transformation from a single monoclinically distorted tetragonal-like phase to a complex mixed-phase structure in films with thicknesses up to ~200 nm is the consequence of a strain-induced spinodal instability in the BiFeO3/LaAlO3 system. Additionally, a breakdown of this strain-stabilized metastable mixed-phase structure to non-epitaxial microcrystals of the parent rhombohedral structure of BiFeO3 is observed to occur at a critical thickness of ~300 nm. We further propose a mechanism for this abrupt breakdown that provides insight into the competing nature of the phases in this system.Comment: 7 figure

Direct Measurement of Pyroelectric and Electrocaloric Effects in Thin Films

An understanding of polarization-heat interactions in pyroelectric and electrocaloric thin-film materials requires that the electrothermal response is reliably characterized. While most work, particularly in electrocalorics, has relied on indirect measurement protocols, here we report a direct technique for measuring both pyroelectric and electrocaloric effects in epitaxial ferroelectric thin films. We demonstrate an electrothermal test platform where localized high-frequency (approximately 1 kHz) periodic heating and highly sensitive thin-film resistance thermometry allow the direct measurement of pyrocurrents (<10 pA) and electrocaloric temperature changes (<2 mK) using the “2-omega” and an adapted “3-omega” technique, respectively. Frequency-domain, phase-sensitive detection permits the extraction of the pyrocurrent from the total current, which is often convoluted by thermally-stimulated currents. The wide-frequency-range measurements employed in this study further show the effect of secondary contributions to pyroelectricity due to the mechanical constraints of the substrate. Similarly, measurement of the electrocaloric effect on the same device in the frequency domain (at approximately 100 kHz) allows for the decoupling of Joule heating from the electrocaloric effect. Using one-dimensional, analytical heat-transport models, the transient temperature profile of the heterostructure is characterized to extract pyroelectric and electrocaloric coefficients

Phase coexistence and electric-field control of toroidal order in oxide superlattices

Systems that exhibit phase competition, order parameter coexistence, and emergent order parameter topologies constitute a major part of modern condensed-matter physics. Here, by applying a range of characterization techniques, and simulations, we observe that in PbTiO>3/SrTiO>3 superlattices all of these effects can be found. By exploring superlattice period-, temperature- and field-dependent evolution of these structures, we observe several new features. First, it is possible to engineer phase coexistence mediated by a first-order phase transition between an emergent, low-temperature vortex phase with electric toroidal order and a high-temperature ferroelectric a>1/a>2 phase. At room temperature, the coexisting vortex and ferroelectric phases form a mesoscale, fibre-textured hierarchical superstructure. The vortex phase possesses an axial polarization, set by the net polarization of the surrounding ferroelectric domains, such that it possesses a multi-order-parameter state and belongs to a class of gyrotropic electrotoroidal compounds. Finally, application of electric fields to this mixed-phase system permits interconversion between the vortex and the ferroelectric phases concomitant with order-of-magnitude changes in piezoelectric and nonlinear optical responses. Our findings suggest new cross-coupled functionalities.A.R.D. acknowledges support from the Army Research Office under grant W911NF-14-1-0104 and the Department of Energy, Office of Science, Office of Basic Energy Sciences under grant no. DE-SC0012375 for synthesis and structural study of the materials. Z.H. acknowledges support from NSF-MRSEC grant number DMR-1420620 and NSF-MWN grant number DMR-1210588. A.K.Y. acknowledges support from the Office of Basic Energy Sciences, US Department of Energy DE-AC02-05CH11231. C.T.N. acknowledge support from the Office of Basic Energy Sciences, US Department of Energy DE-AC02-05CH11231. S.L.H. acknowledges support from the National Science Foundation under the MRSEC programme (DMR-1420620). M.R.M. acknowledges support from the National Science Foundation Graduate Research Fellowship under grant number DGE-1106400. K.-D.P., V.K. and M.B.R. acknowledge support from the US Department of Energy, Office of Basic Sciences, Division of Material Sciences and Engineering, under Award No. DE-SC0008807. A.F. acknowledges support from the Swiss National Science Foundation. P.G.-F. and J.J. acknowledge financial support from the Spanish Ministry of Economy and Competitiveness through grant number FIS2015-64886-C5-2-P. J.I. is supported by the Luxembourg National Research Fund (Grant FNR/C15/MS/10458889 NEWALLS). L.-Q.C. is supported by the US Department of Energy, Office of Basic Energy Sciences under Award FG02-07ER46417. R.R. and L.W.M. acknowledge support from the Gordon and Betty Moore Foundation’s EPiQS Initiative, under grant GBMF5307. The Advanced Light Source is supported by the Director, Office of Science, Office of Basic Energy Sciences, of the US Department of Energy under Contract No. DE-C02-05CH11231. Nanodiffraction measurements were supported by the US Department of Energy, Office of Science, Office of Basic Energy Sciences, Materials Sciences and Engineering Division. This research used resources of the Advanced Photon Source, a US Department of Energy (DOE) Office of Science User Facility operated for the DOE Office of Science by Argonne National Laboratory under Contract No. DE-AC02-06CH11357. Electron microscopy of superlattice structures was performed at the Molecular Foundry at Lawrence Berkeley National Laboratory, supported by the Office of Science, Office of Basic Energy Sciences, US Department of Energy (DE-AC02-05CH11231).Peer Reviewe

THE HERMENEUTICAL RECEPTION OF THE CHARACTER OF JORGE DE BURGOS IN UMBERTO ECO\u27S NOVEL "THE NAME OF THE ROSE"

U članku se analiziraju modaliteti Ecova intertekstualnog prisvajanja fikcionalne osobe J.L. Borgesa i pojedinih književnih metafora koje se razvijaju u njegovim pripovijetkama u izgradnji hermeneutičke recepcije lika Jorgea iz Burgosa, glavnog negativca romana Ime ruže Umberta Eca. Dok je prvi aspekt dostatno obrađen u kritičkoj literaturi o Imenu ruže, drugi je ostao zanemaren u nekim bitnim aspektima. Analiza ideoloških i hermeneutičkih aspekata njegovog lika u Ecovu romanu otkriva da u izgradnji ne samo njegova etičkog i teološkog habitusa nego i razvitku glavnog narativnog tijeka romana, čiji je on pokretač, veliku ulogu igraju dvostruko kodirane metafore koje Borges razvija u svojim pripovijetkama Teolozi i Tri tumačenja Jude. U članku se analizira njihova uloga u spomenutim Borgesovim novelama i njihov intertekstualni odjek u Imenu ruže koji se pronalazi na idejnoj i kompozicijsko-pripovjednoj razini. Temeljna Borgesova metafora \u27svi su ljudi jedan čovjek\u27 razrađuje se u romanu raznim figurama ponavljanja, a unutar te primarne metafore značajna je metaforika Jude koju Borges razvija u noveli Tri tumačenja Jude. Analiza hermeneutičke recepcije Jorgeova lika otkriva presudnu ulogu te metafore u njenoj iozgradnji.This article analyses the modalities of Umberto Eco\u27s intertextual adoption of J. L. Borges\u27 \u27fictional person\u27 and the specific literary metaphors Borges developed and used in his short stories when building the hermeneutical reception of the character of Jorge de Burgos, the villain of Eco\u27s novel The Name of the Rose. While the critical literature on The Name of the Rose has devoted considerable attention to the former, the latter has remained neglected in some crucial aspects. The analysis of ideological and hermeneutic aspects of his character in Eco\u27s novel revealed that, in creating his ethical and theological habitus and even in the development of the novel\u27s main narrative, a significant role was played by double coded metaphors developed by Borges in his short stories The Theologians and Three Versions of Judas. This article analyses their role in the aforementioned short stories by Borges and their intertextual resonance in The Name of the Rose visible both, on the level of ideas and the compositional-narrative level. The basic Borges\u27 metaphor, "Whatever one man does, it is as if all men did it", was developed in the novel with the help of various figures of repetition. Within that primary metaphor, an important place is held by the metaphorics of Judas developed by Borges in Three Versions of Judas. Analysis of the hermeneutical reception of Jorge\u27s character has revealed the crucial role of that metaphor in its creation