Temperature Driven Structural Phase Transition in Tetragonal-Like BiFeO3

Highly-strained BiFeO3 exhibits a "tetragonal-like, monoclinic" crystal structure found only in epitaxial films (with an out-of-plane lattice parameter exceeding the in-plane value by >20%). Previous work has shown that this phase is properly described as a M$_{C}$ monoclinic structure at room temperature [with a (010)$_{pc}$ symmetry plane, which contains the ferroelectric polarization]. Here we show detailed temperature-dependent x-ray diffraction data that evidence a structural phase transition at ~100C to a high-temperature M$_{A}$ phase ["tetragonal-like" but with a (1-10)$_{pc}$ symmetry plane]. These results indicate that the ferroelectric properties and domain structures of strained BiFeO$_3$ will be strongly temperature dependent.Comment: 10 pages, 3 figure

Large electric-field induced strain in BiFeO3 ceramics

Large bipolar strain of up to 0.36% (peak-to-peak value) was measured in BiFeO3 ceramics at low frequency (0.1 Hz) and large amplitude (140 kV/cm) of the driving field. This strain is comparable to that achievable in highly efficient Pb-based perovskite ceramics, such as Pb(Zr,Ti)O3 and Pb(Mg,Nb)O3-PbTiO3. The strain showed a strong dependence on the field frequency and is likely largely associated with domain switching involving predominantly non-180{\deg} domain walls. In addition, rearrangement of charged defects by applying electric field of low frequency depins these domain walls, resulting in a more efficient switching and, consequently, an increased response

Growing Our Own: A Proposal for the Development of a Nurse Mentoring Program

The process of mentoring is not a new concept in the world of business or in the world of health care. Mentoring has been implemented in many organizations and disciplines throughout the world and has been shown to yield many benefits including employee satisfaction, personal and professional growth, and organizational loyalty. This paper proposes a process to develop a nurse mentoring program for the Department of Nursing at Mayo Clinic. Highlights of the benefits that can be realized with the implementation of a nurse mentoring program, supporting literature and research, and challenges and barriers encountered when developing this proposal will be reviewed. In addition, Jean Watson\u27s Theory of Human Caring will be endorsed as the foundation for the nurse mentoring program for the Department of Nursing at Mayo Clinic in Rochester, Minnesota. This paper will explain why a nurse mentoring program based on Watson\u27s concepts of caring can be a valuable tool that will provide gains to the participants in the program, the Department of Nursing, the organization, and the patients

Low-Symmetry Monoclinic Phases and Polarization Rotation Path Mediated By Epitaxial Strain in Multiferroic BiFeO3 Thin Films

A morphotropic phase boundary driven by epitaxial strain has been observed in a lead-free multiferroic BiFeO3 thin films and the strain-driven phase transitions were widely reported to be iso-symmetric Cc-Cc ones by recent works. In this paper, we suggest that the tetragonal-like BiFeO3 phase identified in epitaxial films on (001) LaAlO3 single crystal substrates is monoclinic MC. This MC phase is different from MA type monoclinic phase reported in BiFeO3 films grown on low mismatch substrates, such as SrTiO3. This is confirmed not only by synchrotron x-ray studies but also by piezoresponse force microscopy measurements. The polarization vectors of the tetragonal-like phase lie in the (100) plane, not the (110) plane as previously reported. A phenomenological analysis was proposed to explain the formation of MC Phase. Such a low symmetry MC phase, with its linkage to MA phase and the multiphase coexistence open an avenue for large piezoelectric response in BiFeO3 films and shed light on a complete understanding towards possible polarization rotation paths and enhanced multiferroicity in BiFeO3 films mediated by epitaxial strain. This work may also aid the understanding of developing new lead-free strain-driven morphotropic phase boundary in other ferroic systems.Comment: 22 pages,Submitted to Advanced Functional Materials on Sep,7,2010, accepted on Oct,27,201

Intrathekale Baclofentherapie in der Frührehabilitation bei Kindern und Jugendlichen mit postneonatal erworbener hypoxisch-ischämischer Encephalopathie

Kinder und Jugendliche befinden sich in der Frührehabilitationsphase nach postneonatal erworbenen hypoxisch-ischämischen Hirnschädigungen häufig in einem schwer kranken Zustand mit Bewusstseinsstörung, generalisierter Muskeltonuserhöhung, häufig mit vegetativen Krisen, Schmerzen und psychomotorischer Unruhe. In vielen Fällen sind diese Zustände medikamentös ungenügend beeinflussbar. Zielsetzung der vorliegenden, retrospektiven Arbeit war, die Auswirkungen der intrathekalen Baclofentherapie (ITB) bei solchermaßen betroffenen Patienten zu untersuchen. Eingeschlossen wurden 46 pädiatrische Patienten, bei denen im Zeitraum von Juli 1986 bis Dezember 2007 an der Schön Klinik Vogtareuth auf Grund der Symptome einer jenseits der Neonatalperiode erworbenen hypoxisch-ischämischen Encephalopathie eine intrathekale Baclofentherapie (ITB) durchgeführt wurde, bei denen die Implantation des Pumpensystems innerhalb eines Jahres nach dem hypoxischen Ereignis erfolgte und die im Anschluss noch mindestens vier Wochen an der Klinik behandelt wurden. Die Analyse der Daten erbrachte folgende Ergebnisse: 1. Nach Beginn einer ITB verbesserten sich bei 42 / 46 der Patienten der muskuläre Hypertonus, bei 13 / 17 die dystone Komponente der Bewegungsstörung sowie bei 31 / 33 eine vegetative Dysregulation. Medikamente mit sedierender Haupt- oder Nebenwirkung konnten bei 24 / 46 Patienten innerhalb von zwölf Wochen nach Implantation reduziert, bei mindestens 20 / 46 Patienten sogar vollständig abgesetzt werden. 2. Behandlungsbedürftige Komplikationen traten nach der Implantation des Pumpen-Katheter-Systems bei 21 / 46 Patienten während der Frührehabilitation auf. Fünf Pumpen mussten komplikationsbedingt explantiert werden. Die Rate an Komplikationen war mit zunehmendem Implantationsjahr signifikant abnehmend. Für keinen der anderen hypothetischen Einflussfaktoren (Alter der Patienten, vorausgegangene intrathekale Baclofentestung mittels Intraspinalkatheter, Außenhöhe der Pumpenmodelle) konnte ein Einfluss auf das Komplikationsrisiko nachgewiesen werden. 3. Bei 29 der 46 Patienten kam es während der ITB zur Verbesserung des Bewusstseinsstadiums, bei weiteren neun Patienten zu subtileren Verbesserungen der Bewusstseinslage, Wahrnehmungsfähigkeit und / oder Aufmerksamkeit und somit der Rehabilitationsfähigkeit. Bei sechs Patienten normalisierte sich die Bewusstseinslage. Hier war die Abgrenzung zwischen Spontanverlauf und spezifischem Effekt der ITB besonders schwierig. Auch wenn die Evidenz der vorliegenden Studie durch das retrospektive Design eingeschränkt ist, konnte gezeigt werden, dass die intrathekale Baclofentherapie gut geeignet ist, schwerwiegende Tonuserhöhungen und vegetative Krisen in der Subakutphase nach postneonatal erworbener Hirnschädigung bei pädiatrischen Patienten positiv zu beeinflussen. Vor dem Hintergrund des meist schweren Leidens der Patienten handelt es sich daher bei diesen Patienten, trotz der möglichen Komplikationen (die an Zentren mit langjähriger Erfahrung weniger häufig auftreten) um ein dringend empfehlenswertes Verfahren. Die ITB führt über die Linderung der zuvor quälenden Zustände der Patienten und die Ermöglichung einer Medikamentenreduktion zu verbesserten Voraussetzungen für eine Erholung der neurologischen Symptome und könnte somit auch eine oftmals beobachtete Verbesserung der Bewusstseinslage begünstigen

Stabilization of weak ferromagnetism by strong magnetic response to epitaxial strain in multiferroic BiFeO3

Multiferroic BiFeO3 exhibits excellent magnetoelectric coupling critical for magnetic information processing with minimal power consumption. However, the degenerate nature of the easy spin axis in the (111) plane presents roadblocks for real world applications. Here, we explore the stabilization and switchability of the weak ferromagnetic moments under applied epitaxial strain using a combination of first-principles calculations and group-theoretic analyses. We demonstrate that the antiferromagnetic moment vector can be stabilized along unique crystallographic directions ([110] and [-110]) under compressive and tensile strains. A direct coupling between the anisotropic antiferrodistortive rotations and the Dzyaloshinskii-Moria interactions drives the stabilization of the weak ferromagnetism. Furthermore, energetically competing C- and G-type magnetic orderings are observed at high compressive strains, suggesting that it may be possible to switch the weak ferromagnetism "on" and "off" under the application of strain. These findings emphasize the importance of strain and antiferrodistortive rotations as routes to enhancing induced weak ferromagnetism in multiferroic oxides.ope

Concurrent transition of ferroelectric and magnetic ordering near room temperature

Strong spin-lattice coupling in condensed matter gives rise to intriguing physical phenomena such as colossal magnetoresistance and giant magnetoelectric effects. The phenomenological hallmark of such a strong spin-lattice coupling is the manifestation of a large anomaly in the crystal structure at the magnetic transition temperature. Here we report that the magnetic Néel temperature of the multiferroic compound BiFeO3 is suppressed to around room temperature by heteroepitaxial misfit strain. Remarkably, the ferroelectric state undergoes a first-order transition to another ferroelectric state simultaneously with the magnetic transition temperature. Our findings provide a unique example of a concurrent magnetic and ferroelectric transition at the same temperature among proper ferroelectrics, taking a step toward room temperature magnetoelectric applications. © 2011 Macmillan Publishers Limited. All rights reserved.open435

Temperature dependent piezoelectric response and strain–electric-field hysteresis of rare-earth modified bismuth ferrite ceramics

The rare-earth (RE)-modified bismuth ferrite (BiFeO3 or BFO) family of ferroelectrics have uncomplicated lead-free chemistries and simple perovskite structures. Due to the high Curie transition temperature of the parent BiFeO3 perovskite (∼830 °C), they are promising piezoelectric materials for use at elevated temperatures. However, the influence of the specific RE species on the electromechanical behavior at high temperatures and above the coercive electric-field is not widely reported. Here, structural analysis over multiple length scales using X-ray diffraction, transmission electron microscopy and piezoresponse force microscopy is coupled with a high electric-field cycling study and in situ converse d33 measurements up to 325 °C for three RE–BFO ceramic compositions, Bi0.86Sm0.14FeO3, Bi0.88Gd0.12FeO3 and Bi0.91Dy0.09FeO3. The ceramics exhibit different phase assemblages with varying amounts of polar rhombohedral R3c and intermediate antipolar orthorhombic Pbam phases as a function of the RE species. During electric-field cycling at electric-fields with amplitudes of 160 kV cm−1, peak-to-peak strains of 0.23–0.27% are reached for all three compositions. However, there are qualitative differences in the field-induced strain and electric current behavior as a function of electric-field cycling and the materials exhibit an electrical-history dependent behavior. Bi0.91Dy0.09FeO3 possesses an improved d33 stability as a function of temperature relative to the parent BFO perovskite and the highest depolarization temperature among the three RE–BFO compositions, with a stable d33 of ∼22 pC N−1 up to 325 °C

Nanostructuring Ferroelectrics via Focused Ion Beam Methodologies

As we reach the physical limit of Moore’s law and silicon based electronics, alternative schemes for memory and sensor devices are being proposed ona regular basis. The properties of ferroelectric materials on the nanoscale are key to developing device applications of this intriguing material class, and nanostructuring has been readily pursued in recent times. Focused ion beam (FIB) microscopy is one of the most signi cant techniques for achievingthis. When applied in tandem with the imaging and nanoscale manipulation afforded by proximal scanning force microscopy tools, FIB-driven nanoscale characterization has demonstrated the power and ability which simply may not be possible by other fabrication techniques in the search for innovative and novel ferroic phenomena. At the same time the process is not without pitfalls; it is time-consuming and success is not always guaranteed thus often being the bane in progress. This balanced review explores a brief history of the relationship between the FIB and ferroelectrics, the fascinating properties it has unveiled, the challenges associated with FIB that have led to alterna- tive nanostructuring techniques and nally new ideas that should be explored using this exciting technique

Pause Structure in Narratives of Neurologically Impaired and Control Subjects

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