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20 Aug 2012

Volume 101, Issue 8, Articles (08xxxx)

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Appl. Phys. Lett. 101, 081102 (2012); http://dx.doi.org/10.1063/1.4745791 (3 pages)

M. K. Wu, M. Feng, and N. Holonyak, Jr.
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Antiferroelectric-like properties and enhanced polarization of Cu-doped K0.5Na0.5NbO3 piezoelectric ceramics

S. M. Ke, H. T. Huang, H. Q. Fan, H. K. Lee, L. M. Zhou, and Y.-W. Mai

Appl. Phys. Lett. 101, 082901 (2012); http://dx.doi.org/10.1063/1.4747212 (4 pages)

Online Publication Date: 20 August 2012

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Abnormal evolution of ferroelectric hysteresis (P-E) loops was observed in Cu-doped K0.5Na0.5NbO3 (KNN) ceramics. The 1 mol. % Cu-doped fresh sample exhibited double-loop-like characteristics, while the 1.5 and 2 mol. % Cu-doped KNN ceramics showed normal single loops. Electron paramagnetic resonance spectra verified the formation of non-switchable (CuNb‴−VO••) ′ (DC1) and non-polar (VO••−CuNb‴−VO••)• (DC2) defect complexes in these ceramics. According to the experimental results, it is suggested that DC1 would provide the driving force for domain back-switching, leading to the double P-E loops, while DC2 would contribute to the space charges. Dielectric aging behaviors of the samples also supported this mechanism. It is the competition between the DC1 and DC2 defect complexes that induced the observed compositional evolution of P-E loops in the Cu-doped KNN ceramics.
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77.80.Dj Domain structure; hysteresis
77.80.Fm Switching phenomena
77.84.Ek Niobates and tantalates
76.30.-v Electron paramagnetic resonance and relaxation
77.22.Ej Polarization and depolarization
77.22.Jp Dielectric breakdown and space-charge effects

Observation of direct and indirect magnetoelectricity in lead free ferroelectric (Na0.5Bi0.5TiO3)–magnetostrictive (CoFe2O4) particulate composite

A. Srinivas, R. V. Krishnaiah, T. Karthik, P. Suresh, Saket Asthana, and S. V. Kamat

Appl. Phys. Lett. 101, 082902 (2012); http://dx.doi.org/10.1063/1.4745840 (5 pages)

Online Publication Date: 20 August 2012

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A particulate composite consisting of 65 mol. % Na0.5Bi0.5TiO3 and 35 mol. % CoFe2O4 was synthesized, and it’s structure, microstructure, ferroelectric, magnetostrictive, magnetic, and direct/indirect magnetoelectric properties were studied. The composite showed different magnetization behaviour under electrically poled and un-poled conditions. The percentage change in magnetization as a result of poling is approximately −15% at 500 Oe magnetic field. Magnetostriction measurements displayed a value of λ11 = −57 × 10−6 and piezomagnetic coefficient δλ11/δH = 0.022 × 10−6 kOe−1 at 2.2 kOe for the composite. The maximum magnetoelectric output varied from 1350 mV/cm to 2000 mV/cm with change in the electrical poling conditions.
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75.85.+t Magnetoelectric effects, multiferroics
75.50.Tt Fine-particle systems; nanocrystalline materials
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.80.+q Magnetomechanical effects, magnetostriction
77.22.Ej Polarization and depolarization
77.80.-e Ferroelectricity and antiferroelectricity

Characteristics of long gap surface flashover channel in vacuum under nanosecond quasi-square pulses

Xin-Bing Cheng, Jin-Liang Liu, and Bao-Liang Qian

Appl. Phys. Lett. 101, 082903 (2012); http://dx.doi.org/10.1063/1.4746262 (3 pages) | Cited 1 time

Online Publication Date: 20 August 2012

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High-voltage vacuum insulator failure is generally due to surface flashover rather than insulator bulk breakdown. To study the characteristic of surface flashover channel, a diagnosis system to obtain the images of flashover channel is fabricated using a high speed frame camera, and results are presented by an investigation into the flashover of poly-methyl methacrylate insulator with gap spacing of 170 mm in vacuum under 180 ns quasi-square pulses. It is obtained that after formation of the flashover channel, the impedance of the flashover channel is inductive and the waveform of the measured voltage is determined by the inductance of the flashover channel directly.
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52.80.Vp Discharge in vacuum
52.25.Fi Transport properties
52.70.Kz Optical (ultraviolet, visible, infrared) measurements

Maximizing the number of coexisting phases near invariant critical points for giant electrocaloric and electromechanical responses in ferroelectrics

Z. K. Liu, Xinyu Li, and Q. M. Zhang

Appl. Phys. Lett. 101, 082904 (2012); http://dx.doi.org/10.1063/1.4747275 (4 pages) | Cited 4 times

Online Publication Date: 21 August 2012

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Ferroelectric materials directly convert electrical energy to mechanical or thermal work and are critical to applications such as sensors, transducers, actuators, and cooling devices. Numerous efforts have been undertaken to develop materials with high electrocaloric (EC) and electromechanical (EM) responses. Here, we present a theoretical analysis, based on thermodynamic fundamentals, for developing ferroelectric materials with high EC and EM responses, i.e., searching for and operating the material near an invariant critical point (ICP). We show that by tailoring the constraints to maximize the number of coexisting phases near ICPs, large EC and EM responses may be realized.
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77.70.+a Pyroelectric and electrocaloric effects
77.80.-e Ferroelectricity and antiferroelectricity
77.65.-j Piezoelectricity and electromechanical effects

Co-sputtering yttrium into hafnium oxide thin films to produce ferroelectric properties

T. Olsen, U. Schröder, S. Müller, A. Krause, D. Martin, A. Singh, J. Müller, M. Geidel, and T. Mikolajick

Appl. Phys. Lett. 101, 082905 (2012); http://dx.doi.org/10.1063/1.4747209 (4 pages)

Online Publication Date: 22 August 2012

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Thin film capacitors were fabricated by sputtering TiN-Y doped HfO2-TiN stacks on silicon substrates. Yttrium was incorporated into the HfO2 layers by simultaneously sputtering from Y2O3 and HfO2 sources. Electric polarization and relative permittivity measurements yield distinct ferroelectric properties as a result of low yttrium dopant concentrations in the range of 0.9-1.9 mol. %. Grazing incidence x-ray diffraction measurements show the formation of an orthorhombic phase in this range. Compared to atomic layer deposition films, the highest remanent polarization and the highest relative permittivity were obtained at significantly lower doping concentrations in these sputtered films.
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81.15.Cd Deposition by sputtering
84.32.Tt Capacitors
77.55.-g Dielectric thin films
77.22.Ch Permittivity (dielectric function)
77.22.Ej Polarization and depolarization
77.80.-e Ferroelectricity and antiferroelectricity

Characterization and modeling of trap number and creation time distributions under negative-bias-temperature stress

Jung-Piao Chiu, Chi-Wei Li, and Tahui Wang

Appl. Phys. Lett. 101, 082906 (2012); http://dx.doi.org/10.1063/1.4748108 (3 pages)

Online Publication Date: 24 August 2012

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Individual trapped charge creations and a trap number in p-type metal-oxide-semiconductor field effect transistors (pMOSFETs) under negative bias temperature instability (NBTI) stress are investigated. We find that the characteristic times of a trapped charge creation scatter over several decades of time in small area pMOSFETs, which is attributed to an activation energy distribution in the reaction-diffusion (RD) model of NBTI. We develop a statistical model by combining the RD model with an extracted activation energy distribution to calculate a threshold voltage shift distribution at different NBTI stress times. Our model agrees with measured results very well.
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85.30.Tv Field effect devices
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