Electroforming free high resistance resistive switching of graphene oxide modified polar-PVDF

Future nanoelectronics for nonvolatile memory elements require novel materials and devices that can switch logic states with a low power consumption, minimum heat dissipation, high-circuit density, fast switching speed, large endurance and long charge retention period. Herein, we report novel high resistance resistive switching in a polar beta-polyvinylidene fluoride (beta-PVDF) and graphene oxide (GO) composite. A high resistance switching ratio was achieved without the realization of the essential current-filament forming condition mainly responsible for switching the device from high to low resistance states. beta-PVDF is a well known ferroelectric/piezoelectric material which changes shape and size after application of an external electric field. We propose a model which describes how the present beta-PVDF-GO composite changes shape after application of an external electric field (E) which provides a favorable environment for the formation of the current linkage path of GO in the PVDF matrix. The applied positive SET electric fields (+E) switch the composite from a high to a low resistance state, which further re-switches from a low to a high resistance state under negative RE-SET electric fields (-E). The positive and negative E-fields are responsible for the contraction and expansion of beta-PVDF, respectively, redox reactions between GO and adsorbed water, oxygen migrations, and/or metal diffusion from the electrode to the beta-PVDF-GO matrix. The above mentioned characteristics of the composite allows switching from one high resistance state to another high resistance state. The switching current lies below the range of 10-100 mu A with an exceptionally high switching ratio, which meets one of the prerequisite criteria of low power nanoelectronics memristors

Experimental verification of the ab initio phase transition sequence in SrZrO3 and comparisons with SrHfO3 and SrSnO3

AK acknowledges the CSIR-National Physical Laboratoryinternal net work project, INDIA. Hitesh Borkar would like to acknowledge the CSIR (SRF) to provide fellowship to carry out PhD program.We present detailed Raman studies of SrZrO3 (SZO) that show three anomalies in Raman modes:One has a small jump in frequency ω; one has its intensity vanish; and a third has a sharp change in temperature derivative dω(T)/dT from flat below T = 600 K to a Curie-Weiss dependence above 600 K with extrapolation to zero frequency at the known transition temperature T = 970K, thereby proving the latter to be displacive. In addition, the P4mm ferroelectric phase predicted at high stresses [Amisi et al., Phy. Rev. B 85, 064112 (2012)] has preliminary support from polarization-voltage experiments. The inference of a new transition in the temperature region 600-650 K is in disagreement with neutron studies. Comparisons are given for family member SrSnO3 and SrHfO3, and we discuss the different conclusions of Kennedy and Knight, J Phys.Condens. Mat. 27, 365401 (2015). We show that a known transition in SrHfO3 is also displacive with a well-behaved soft mode.Publisher PDFPeer reviewe

Novel optically active lead-free relaxor ferroelectric (Ba0.6Bi0.2Li0.2)TiO3

We discovered a near room temperature lead-free relaxor-ferroelectric (Ba0.6Bi0.2Li0.2)TiO3 (BBLT) having A-site compositional disordered ABO3 perovskite structure. Microstructure-property relations revealed that the chemical inhomogeneities and development of local polar nano regions (PNRs) are responsible for dielectric dispersion as a function of probe frequencies and temperatures. Rietveld analysis indicates mixed crystal structure with 80% tetragonal structure (space group P4mm) and 20% orthorhombic structure (space group Amm2) which is confirmed by the high resolution transmission electron diffraction pattern. Dielectric constant and tangent loss dispersion with and without illumination of light obey nonlinear Vogel-Fulture relation. It shows slim polarization-hysteresis (P-E) loops and excellent displacement coefficients (d33 ~ 233 pm/V) near room temperature, which gradually diminish near the maximum dielectric dispersion temperature (Tm). The underlying physics for light-sensitive dielectric dispersion was probed by X-ray photon spectroscopy (XPS) which strongly suggests that mixed valence of bismuth ions, especially Bi5+ ions, are responsible for most of the optically active centers. Ultraviolet photoemission measurements showed most of the Ti ions are in 4+ states and sit at the centers of the TiO6 octahedra, which along with asymmetric hybridization between O 2p and Bi 6s orbitals appears to be the main driving force for net polarization. This BBLT material may open a new path for environmental friendly lead-free relaxor-ferroelectric research.Comment: 23 pages, 5 figure

Anomalous change in leakage and displacement currents after electrical poling on lead-free ferroelectric ceramics

We report the polarization, displacement current and leakage current behavior of a trivalent nonpolar cation Al cation substituted lead free ferroelectric NBT-BT electroceramics with tetragonal phase and P4mm space group symmetry. Nearly three orders of magnitude decrease in leakage current were observed under electrical poling, which significantly improves microstructure, polarization, and displacement current. Effective poling neutralizes the domain pinning, traps charges at grain boundaries and fills oxygen vacancies with free charge carriers in matrix, thus saturated macroscopic polarization in contrast to that in upoled samples. E-poling changes bananas type polarization loops to real ferroelectric loops.Comment: 18 pages, 5 figure

Photoconductivity and photo-detection response of multiferroic bismuth iron oxide

We report visible light detection with in-plane BiFeO3 (BFO) thin films grown on pre-patterned inter-digital electrodes. In-plane configured BFO film displayed photocurrents with a 40:1 photo-to-dark-current ratio and improved photo-sensing ability for >15000 s (4 hrs) under small bias voltage (42V). Nearly sixty percent of the photo-induced charge carriers decay in 1.0 s and follow a double-exponential decay model. At 373 K the effect of light does not significantly increase the dark current, probably due to reduced mobility. Sub-bandgap weak monochromatic light (1 mw/cm2) shows one fold increase in photo-charge carriers.Comment: 18 pages, 7 figure

Giant enhancement in ferroelectric polarization under illumination

AK acknowledges the CSIR-MIST (PSC-0111) project for their financial assistance. Hitesh Borkar would like to acknowledge the UGC (SRF) to provide fellowship to carry out Ph.D program.We report optical enhancement in polarization and dielectric constant near room temperature in Pb0.6Li0.2Bi0.2Zr0.2Ti0.8O3 (PLBZT) electro-ceramics; these are doubly substituted members of the most important commercial ferroelectric PbZr0.2Ti0.8O3 (PZT:20/80). Partial (40%) substitution of equal amounts of Li+1 and Bi+3 in PZT: 20/80 retains the PZT tetragonal structure with space group P4 mm. Under illumination of white light and weak 405 nm near-ultraviolet laser light (30 mW), an unexpectedly large (200-300%) change in polarization and displacement current was observed. Light also changes the dc conduction current density by one to two orders of magnitude with a large switchable open circuit voltage (Vocv ∼ 2 V) and short circuit current (Jscc∼ 5 × 10−8 A). The samples show a photo-current ON/OFF ratio of order 6:1 under illumination of weak light.PostprintPeer reviewe

Effect of surgical experience and spine subspecialty on the reliability of the {AO} Spine Upper Cervical Injury Classification System

OBJECTIVE The objective of this paper was to determine the interobserver reliability and intraobserver reproducibility of the AO Spine Upper Cervical Injury Classification System based on surgeon experience (< 5 years, 5–10 years, 10–20 years, and > 20 years) and surgical subspecialty (orthopedic spine surgery, neurosurgery, and "other" surgery). METHODS A total of 11,601 assessments of upper cervical spine injuries were evaluated based on the AO Spine Upper Cervical Injury Classification System. Reliability and reproducibility scores were obtained twice, with a 3-week time interval. Descriptive statistics were utilized to examine the percentage of accurately classified injuries, and Pearson’s chi-square or Fisher’s exact test was used to screen for potentially relevant differences between study participants. Kappa coefficients (κ) determined the interobserver reliability and intraobserver reproducibility. RESULTS The intraobserver reproducibility was substantial for surgeon experience level (< 5 years: 0.74 vs 5–10 years: 0.69 vs 10–20 years: 0.69 vs > 20 years: 0.70) and surgical subspecialty (orthopedic spine: 0.71 vs neurosurgery: 0.69 vs other: 0.68). Furthermore, the interobserver reliability was substantial for all surgical experience groups on assessment 1 (< 5 years: 0.67 vs 5–10 years: 0.62 vs 10–20 years: 0.61 vs > 20 years: 0.62), and only surgeons with > 20 years of experience did not have substantial reliability on assessment 2 (< 5 years: 0.62 vs 5–10 years: 0.61 vs 10–20 years: 0.61 vs > 20 years: 0.59). Orthopedic spine surgeons and neurosurgeons had substantial intraobserver reproducibility on both assessment 1 (0.64 vs 0.63) and assessment 2 (0.62 vs 0.63), while other surgeons had moderate reliability on assessment 1 (0.43) and fair reliability on assessment 2 (0.36). CONCLUSIONS The international reliability and reproducibility scores for the AO Spine Upper Cervical Injury Classification System demonstrated substantial intraobserver reproducibility and interobserver reliability regardless of surgical experience and spine subspecialty. These results support the global application of this classification system

Conduction Phenomenon of Al3+ Modified Lead Free (Na0.5Bi0.5)(0.92)Ba0.08TiO3 Electroceramics

Choice of proper dopants at A or B-site of ABO(3) perovskite structure can modify the morphotropic phase boundary (MPB), and hence functional properties of polar systems. The chemical nature of donor or acceptor will significantly influence the fundamental properties. Lead-free ferroelectrics have vast potential to replace the lead-based ceramics. The (Na0.5Bi0.5)(1-x)BaxTiO3 (NBT-BT) (at x=0.08) near MPB with small substitution of trivalent cations (Al3+) has been synthesized by solid state reaction route. The aim to choose the trivalent cations (Al3+) was its relatively smaller radii than that of Bi3+ cations to develop the antipolar phases in the ferroelectric ceramic. Structural, morphological and elemental compositional analyses were studied by X-ray diffraction (XRD), Secondary electron microscope (SEM) and Energy-dispersive X-ray spectroscopy (EDAX), respectively. Ferroelectric studies were carried out on various compositions of (Na0.46Bi0.46-xAlxBa0.08)TiO3 (NBAT-BT) (x= 0, 0.05, 0.07, 0.10) electroceramics. It was observed that with increase in concentration of Al the ferroelectricity state changes from soft to hard. Temperature dependent dielectric spectroscopy shows broad dielectric dispersion. The Al doping diminishes the relaxor behavior of NBT-BT ceramics. Impedance spectroscopy shows that electrical resistivity and relaxation frequency decreases with increase in Al-concentration. Modulus spectra indicate that Al significantly change the bulk capacitance of NBT-BT