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7 Jun 2010

Volume 96, Issue 23, Articles (23xxxx)

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Appl. Phys. Lett. 96, 231104 (2010); http://dx.doi.org/10.1063/1.3443734 (3 pages)

Hiroto Sekiguchi, Katsumi Kishino, and Akihiko Kikuchi
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Phase field model of dielectric and magnetic composites

Yu U. Wang

Appl. Phys. Lett. 96, 232901 (2010); http://dx.doi.org/10.1063/1.3446842 (3 pages) | Cited 5 times

Online Publication Date: 7 June 2010

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Phase field model is developed to calculate heterogeneous distributions of polarization, charge, local field, and effective susceptibility of dielectric and magnetic composites with arbitrary multicomponent microstructures. It solves electrostatic and magnetostatic equations in terms of polarization vector field in reciprocal Fourier space, with interphase boundary conditions automatically satisfied without explicitly tracking interphase interfaces. This advantage allows the model to effectively treat arbitrarily complex multicomponent composites and seamlessly incorporate evolving microstructures from composite fabrication simulations. Evolution of internal field distributions and effective properties in composites during self-assembly fabrication process is presented to demonstrate the model’s capability and potential.
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77.84.Lf Composite materials
41.20.Gz Magnetostatics; magnetic shielding, magnetic induction, boundary-value problems
41.20.Cv Electrostatics; Poisson and Laplace equations, boundary-value problems

A modified Landau–Devonshire thermodynamic potential for strontium titanate

G. Sheng, Y. L. Li, J. X. Zhang, S. Choudhury, Q. X. Jia, V. Gopalan, D. G. Schlom, Z. K. Liu, and L. Q. Chen

Appl. Phys. Lett. 96, 232902 (2010); http://dx.doi.org/10.1063/1.3442915 (3 pages) | Cited 2 times

Online Publication Date: 7 June 2010

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The range of reported values of the Landau energy coefficients of bulk SrTiO3 leads to uncertainty in not only the magnitude but also the direction of the calculated spontaneous polarization in SrTiO3 thin films in a state of biaxial tension. In this study, we use experimental results from strained SrTiO3 films together with phase-field simulations to refine the values of the Landau energy coefficients and report a modified thermodynamic potential for bulk strontium titanate. The transition temperatures and ferroelectric/antiferrodistortive domain stabilities predicted from this modified potential agree well with measurements on biaxially strained SrTiO3 thin films.
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65.40.G- Other thermodynamical quantities
77.80.B- Phase transitions and Curie point

Impact of interface controlling layer of Al2O3 for improving the retention behaviors of In–Ga–Zn oxide-based ferroelectric memory transistor

Sung-Min Yoon, Shin-Hyuk Yang, Soon-Won Jung, Chun-Won Byun, Sang-Hee Ko Park, Chi-Sun Hwang, Gwang-Geun Lee, Eisuke Tokumitsu, and Hiroshi Ishiwara

Appl. Phys. Lett. 96, 232903 (2010); http://dx.doi.org/10.1063/1.3452339 (3 pages) | Cited 11 times

Online Publication Date: 10 June 2010

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We characterized the nonvolatile memory thin-film transistors, which was composed of an amorphous indium-gallium-zinc oxide (α-IGZO) active channel and a ferroelectric poly(vinylidene fluoride-trifluoroethylene) [P(VDF-TrFE)] gate insulator, and investigated the impact of an interface controlling layer. Excellent device performances, such as the field-effect mobility of 60.9 cm2 V−1 s−1, the subthreshold swing of 120 mV/dec, and the memory window of 6.4 V at ±12 V programming, were confirmed for the device without any interface layer. However, the memory retention time was very short. The retention behaviors could be dramatically improved when 4 nm thick Al2O3 layer was introduced between the P(VDF-TrFE) and α-IGZO.
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85.50.Gk Non-volatile ferroelectric memories
85.30.Tv Field effect devices
84.30.Sk Pulse and digital circuits

Phase diagram of ferroelectric nanowires and its mechanical force controllability

S. P. Lin, Yue Zheng, M. Q. Cai, and Biao Wang

Appl. Phys. Lett. 96, 232904 (2010); http://dx.doi.org/10.1063/1.3446854 (3 pages) | Cited 8 times

Online Publication Date: 10 June 2010

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A phenomenological thermodynamic model of ferroelectric nanowires is developed to investigate the size-temperature phase diagrams. Considering existence of the surface tension, size, and external applied stress effects, the approximated expressions of the transition temperatures at which the paraelectric phase loses its stability with respect to the appearance of the spontaneous polarization are derived. At the same time, the size-temperature phase diagrams as functions of the ferroelectric nanowire radius are obtained, and also show its external mechanical stress controllability.
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81.30.Dz Phase diagrams of other materials
81.30.Bx Phase diagrams of metals, alloys, and oxides
77.80.-e Ferroelectricity and antiferroelectricity
77.84.-s Dielectric, piezoelectric, ferroelectric, and antiferroelectric materials

Large three-photon absorption in Ba0.5Sr0.5TiO3 films studied using Z-scan technique

K. Venkata Saravanan, K. C. James Raju, M. Ghanashyam Krishna, Surya P. Tewari, and S. Venugopal Rao

Appl. Phys. Lett. 96, 232905 (2010); http://dx.doi.org/10.1063/1.3447930 (3 pages) | Cited 9 times

Online Publication Date: 10 June 2010

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Large picosecond nonlinearities in Ba0.5Sr0.5TiO3 thin films, grown at different temperatures in situ on (100) MgO substrates using rf magnetron sputtering technique, were studied using the Z-scan technique. The nonlinear absorption mechanism, studied near 800 nm using ∼ 2 and 25 ps pulses, switched from reverse saturable absorption type in the films deposited at temperature<600 °C to three-photon absorption (3PA) in the films deposited at temperature>600 °C. The magnitude of the 3PA coefficient was estimated to be ∼ 10−21 cm3/W2. Two-photon absorption (2PA) was the dominant mechanism recorded with ∼ 6 ns pulses. The observed behavior is correlated with morphological and crystallographic texture of the films. The linear refractive index and optical band gap of the films have also been calculated and these show a strong dependence on the substrate temperature.
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78.66.Nk Insulators
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
68.55.jm Texture
77.84.Cg PZT ceramics and other titanates
81.15.Cd Deposition by sputtering
68.55.A- Nucleation and growth

Density functional theory plus U study of vacancy formations in bismuth ferrite

Zhen Zhang, Ping Wu, Lang Chen, and Junling Wang

Appl. Phys. Lett. 96, 232906 (2010); http://dx.doi.org/10.1063/1.3447369 (3 pages) | Cited 5 times

Online Publication Date: 11 June 2010

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First-principles density functional theory plus U study on the formation enthalpy of BiFeO3 and the intrinsic vacancies was performed. The formation enthalpy of BiFeO3 from oxides is only −0.2 eV, indicating that BiFeO3 could easily decompose into Bi2O3 and Fe2O3 under thermal or electrical stresses. It is found that the vacancy induced local distortions have insignificant effect on the ferroelectric property, thanks to the high stability of the ferroelectric configuration in BiFeO3. Moreover, Bi and Fe vacancies have comparable formation energies, and become dominant in the oxygen rich conditions, leading to p-type conductivity.
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61.72.jd Vacancies
65.40.G- Other thermodynamical quantities
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