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18 Jun 2012

Volume 100, Issue 25, Articles (25xxxx)

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Appl. Phys. Lett. 100, 252401 (2012); http://dx.doi.org/10.1063/1.4727909 (4 pages)

Ming Yan, Christian Andreas, Attila Kákay, Felipe García-Sánchez, and Riccardo Hertel
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Experimental and ab initio investigations of the x-ray absorption near edge structure of orthorhombic LuMnO3

Y. Hu, C. N. Borca, E. Kleymenov, M. Nachtegaal, B. Delley, M. Janousch, A. Dönni, M. Tachibana, H. Kitazawa, E. Takayama-Muromachi, M. Kenzelmann, C. Niedermayer, T. Lippert, A. Wokaun, and C. W. Schneider

Appl. Phys. Lett. 100, 252901 (2012); http://dx.doi.org/10.1063/1.4729002 (4 pages)

Online Publication Date: 18 June 2012

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X-ray near edge absorption spectroscopy was used to probe the electronic structure of multiferroic orthorhombic LuMnO3 polycrystalline samples and strained, twin-free orthorhombic (1–10) LuMnO3 films grown by pulsed laser deposition on (1–10) YAlO3 substrates. For all o-LuMnO3 samples x-ray near edge absorption spectroscopy spectra reveal that the pre-edge structure is influenced by the increase in MnO6 distortion as a result of the smaller Re-ion or film strain. Furthermore there is clear evidence of anisotropic Mn-O bonding and Mn orbital ordering along the c- and [110] direction. The experimental film and bulk data are in agreement with ab initio simulations.
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71.20.Ps Other inorganic compounds
78.70.Dm X-ray absorption spectra
81.15.Fg Pulsed laser ablation deposition
68.55.aj Insulators
71.15.-m Methods of electronic structure calculations

Dielectric relaxation and magneto-dielectric effect in polycrystalline Bi0.9Ca0.1FeO2.95

B. Ramachandran, A. Dixit, R. Naik, G. Lawes, and M. S. Ramachandra Rao

Appl. Phys. Lett. 100, 252902 (2012); http://dx.doi.org/10.1063/1.4729415 (4 pages) | Cited 3 times

Online Publication Date: 18 June 2012

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We have investigated temperature, frequency, and magnetic field dependent dielectric properties of polycrystalline Bi0.9Ca0.1FeO2.95. Two dielectric anomalies, near 65 K and 260 K, were observed with the anomaly near 65 K exhibiting distinct frequency dependence as the peak temperature shifts with increasing frequency. The low-temperature dielectric relaxation data that can be fitted to a Vogel-Fulcher expression yielding a characteristic relaxation time of ∼10−8 s are four orders larger than that of pure BiFeO3 which may be the resultant of the chemical pressure induced by Ca doping. We also observed a switchable magneto-dielectric response in Bi0.9Ca0.1FeO2.95 at room temperature.
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77.22.Gm Dielectric loss and relaxation
61.72.up Other materials
75.85.+t Magnetoelectric effects, multiferroics

Potential barrier increase due to Gd doping of BiFeO3 layers in Nb:SrTiO3-BiFeO3-Pt structures displaying diode-like behavior

H. Khassaf, G. A. Ibanescu, I. Pintilie, I. B. Misirlioglu, and L. Pintilie

Appl. Phys. Lett. 100, 252903 (2012); http://dx.doi.org/10.1063/1.4729816 (4 pages) | Cited 2 times

Online Publication Date: 19 June 2012

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The rectifying properties of Nb:SrTiO3-Bi1−xGdxFeO3-Pt structures (x = 0, 0.05, 0.1) displaying diode-like behavior were investigated via current-voltage characteristics at different temperatures. The potential barrier was estimated for negative polarity assuming a Schottky-like thermionic emission with injection controlled by the interface and the drift controlled by the bulk. The height of the potential barrier at the Nb:SrTiO3-Bi1−xGdxFeO3 interface increases with Gd doping. The results are explained by the partial compensation of the p-type conduction due to Bi vacancies with Gd doping in addition to the shift of the Fermi level towards the middle of the bandgap with increasing dopant concentration.
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73.40.Ei Rectification
73.40.Ns Metal-nonmetal contacts
79.40.+z Thermionic emission
61.72.jd Vacancies

First-principles insights on the magnetism of cubic SrTi1−xCoxO3−δ

J. M. Florez, S. P. Ong, M. C. Onbaşli, G. F. Dionne, P. Vargas, G. Ceder, and C. A. Ross

Appl. Phys. Lett. 100, 252904 (2012); http://dx.doi.org/10.1063/1.4729830 (5 pages) | Cited 1 time

Online Publication Date: 19 June 2012

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We present hybrid density functional calculations suggesting that magnetism in cubic SrTi1−xCoxO3−δ (STCO) with x = 0.25 is sensitive to the nearest neighbor arrangement of the Co and the presence of oxygen vacancies. Spin polarized calculations for x = 0.25 in which the nearest neighbor (nn) Co spacing is a, matha or matha with a the lattice parameter predict lowest energies for the matha nn separation and favor the ferromagnetic state. Oxygen deficiency (δ = 0.125) lowers the average Co valence state and favors mixed valence and spin states (high spin for the Co adjacent to the vacancy and low for the non-adjacent Co), an increase of the band gap and an expansion of the lattice parameter compared to stoichiometric STCO in which both Co ions are low spin. Predicted configurations of the two neighboring Co ions are (t2g5eg0, t2g5eg0) and (t2g4eg2, t2g6eg0) with average 1.0 and 1.6 μB/Co for stoichiometric and 1-O-vacancy systems, respectively.
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75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
61.66.Bi Elemental solids
61.66.Dk Alloys
71.15.Mb Density functional theory, local density approximation, gradient and other corrections
71.20.Ps Other inorganic compounds
71.55.Ht Other nonmetals
75.50.Dd Nonmetallic ferromagnetic materials

Tailoring non-linear dielectric properties by local field engineering in anisotropic porous ferroelectric structures

Leontin Padurariu, Lavinia Curecheriu, Carmen Galassi, and Liliana Mitoseriu

Appl. Phys. Lett. 100, 252905 (2012); http://dx.doi.org/10.1063/1.4729878 (5 pages) | Cited 2 times

Online Publication Date: 20 June 2012

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A method to control the nonlinear dielectric properties in porous anisotropic ceramics is proposed. The local field distributions in anisotropic porous ceramic structures were determined and the field-induced permittivity was estimated in parallel and perpendicular configurations (with respect to the pore orientation vs. the applied field direction). The predicted tunability behavior agrees well with the measured values obtained for Pb(Zr0.52Ti0.48)Nb0.024O3 ceramics with different anisotropic porosity levels. The paper demonstrates the concept of engineered local fields in porous microstructures for tailoring the permittivity and tunability values and the possibility to increase tunability with reducing permittivity for small porosity levels.
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77.22.Ch Permittivity (dielectric function)
61.43.Gt Powders, porous materials
77.80.-e Ferroelectricity and antiferroelectricity
77.84.Ek Niobates and tantalates

Structure and electrical properties of 〈001〉 textured (Ba0.85Ca0.15)(Ti0.9Zr0.1)O3 lead-free piezoelectric ceramics

S. K. Ye, J. Y. H. Fuh, and L. Lu

Appl. Phys. Lett. 100, 252906 (2012); http://dx.doi.org/10.1063/1.4730378 (4 pages) | Cited 2 times

Online Publication Date: 20 June 2012

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〈001〉 textured (Ba0.85Ca0.15)(Ti0.9Zr0.1)O3 (BCTZ) lead-free piezoelectric ceramics were prepared by templated-grain growth method using BaTiO3 as template. The degree of orientation and the microstructure of the ceramics with different amount of template were investigated. The electrical properties of the textured-ceramics in the optimized condition were dramatically enhanced compared with randomly-oriented BCTZ ceramics. The textured BCTZ ceramics showed high piezoelectric constants d33 = 470 pC/N and d31 = −170 pC/N, and high electromechanical coupling factors kp = 44% and k31 = 22%. In addition, the Curie point of the textured ceramics revealed an increase with the template content.
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77.65.Bn Piezoelectric and electrostrictive constants
81.05.Je Ceramics and refractories (including borides, carbides, hydrides, nitrides, oxides, and silicides)
81.40.Ef Cold working, work hardening; annealing, post-deformation annealing, quenching, tempering recovery, and crystallization
77.80.B- Phase transitions and Curie point
77.22.Ch Permittivity (dielectric function)

Intermolecular interactions and high dielectric energy storage density in poly(vinylidene fluoride-hexafluoropropylene)/poly(vinylidene fluoride) blend thin films

Mojtaba Rahimabady, Kui Yao, Saeid Arabnejad, Li Lu, Victor P. W. Shim, and Davy Cheong Wun Chet

Appl. Phys. Lett. 100, 252907 (2012); http://dx.doi.org/10.1063/1.4730603 (4 pages) | Cited 2 times

Online Publication Date: 22 June 2012

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Homogeneous poly(vinylidene fluoride-hexafluoropropylene) and poly (vinylidene fluoride) (P(VDF-HFP)/PVDF) blend films were prepared via a chemical solution approach, followed by quenching, annealing, and hot pressing. The intermolecular interactions of the blends were investigated through atomic simulation. Higher melting temperature, higher crystallinity, larger elastic modulus, and improved breakdown strength (>850 MV/m) were observed in the optimized polymer blends, in comparison with either of the two constituent polymers, PVDF or P(VDF-HFP). In addition, the P(VDF-HFP)/PVDF blend film also showed larger dielectric constant. As a result, an extremely high energy density of 30.1 J/cm3 was achieved in P(VDF-HFP)/PVDF (50:50 by weight) blend films.
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77.22.Ch Permittivity (dielectric function)
77.22.Jp Dielectric breakdown and space-charge effects
81.40.Jj Elasticity and anelasticity, stress-strain relations
62.20.de Elastic moduli
68.55.am Polymers and organics
61.41.+e Polymers, elastomers, and plastics

Epitaxial growth and capacitance-voltage characteristics of BiFeO3/CeO2/yttria-stabilized zirconia/Si(001) heterostructure

Zhongqiang Hu, Meiya Li, Yongdan Zhu, Shizhou Pu, Xiaolian Liu, Bobby Sebo, Xingzhong Zhao, and Shuxiang Dong

Appl. Phys. Lett. 100, 252908 (2012); http://dx.doi.org/10.1063/1.4730621 (4 pages) | Cited 1 time

Online Publication Date: 22 June 2012

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We report the epitaxial growth of multiferroic BiFeO3 (BFO) film on Si(001) substrate by pulsed laser deposition using CeO2/yttria-stabilized zirconia (YSZ) as buffer layers. The epitaxial relationships of the films were BFO(001)/CeO2(001)/YSZ(001)/Si(001) for out-of-plane and [110]BFO‖[100]CeO2‖[100]YSZ‖[100]Si for in-plane, respectively. Capacitance-voltage characteristics of a Pt/BFO/CeO2/YSZ/p-Si capacitor exhibited clockwise hysteresis loops with a large memory window of 2.5 V at sweeping voltages of ±16 V. Both the high and low capacitance values showed no obvious degradation after 104 s. The improved retention property was attributed to the use of high-k CeO2/YSZ insulating layers that effectively eliminated the charge trapping in the heterostructure.
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77.55.fp Other ferroelectric films
73.40.Qv Metal-insulator-semiconductor structures (including semiconductor-to-insulator)
77.80.Dj Domain structure; hysteresis
81.15.Fg Pulsed laser ablation deposition
68.55.aj Insulators
75.85.+t Magnetoelectric effects, multiferroics
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