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5 Jan 2009

Volume 94, Issue 1, Articles (01xxxx)

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Appl. Phys. Lett. 94, 013102 (2009); http://dx.doi.org/10.1063/1.3062938 (3 pages)

Hao-Chih Yuan, Jonghyun Shin, Guoxuan Qin, Lei Sun, Pallab Bhattacharya, Max G. Lagally, George K. Celler, and Zhenqiang Ma
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Anomalous dependence of response time on the electric field in an electroclinic liquid crystal with large induced tilt and polarization

U. Manna, Jang-Kun Song, J. K. Vij, and J. Naciri

Appl. Phys. Lett. 94, 012901 (2009); http://dx.doi.org/10.1063/1.3049319 (3 pages) | Cited 2 times

Online Publication Date: 5 January 2009

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We investigate the response time of an electroclinic liquid crystal with large induced tilt and polarization (de Vries smectic A∗). The response time is found to increase with the increase in electric field up to a threshold value in contrast with the general case of a decrease with field. This behavior is unusual and contrasts with that observed for a conventional smectic-A∗ phase. The anomalous behavior is explained by the Langevin process of the director reorientation by assuming an increase in the effective dipole moment (μeff) with field. The response time decreases with the increase in temperature in the smectic-A∗ phase. We find the existence of a finite correlation length of a few tens of nm which in both temperature and field dependent.
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61.30.Gd Orientational order of liquid crystals; electric and magnetic field effects on order

Macroscopic ferroelectricity and piezoelectricity in nanostructured BiScO3–PbTiO3 ceramics

M. Algueró, H. Amorín, T. Hungría, J. Galy, and A. Castro

Appl. Phys. Lett. 94, 012902 (2009); http://dx.doi.org/10.1063/1.3056660 (3 pages) | Cited 17 times

Online Publication Date: 5 January 2009

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We have studied the macroscopic electrical properties of highly dense, nanostructured ceramics of BiScO3–PbTiO3 with high Curie temperature and piezoelectric activity. Materials were processed by spark plasma sintering of nanocrystalline powder obtained by mechanosynthesis. Results indicate that the nanostructured material still presents the ferroelectric transition above 700 K. Ferroelectric switching is unambiguously demonstrated. Furthermore, ceramic disks were poled and their radial piezoelectric resonance was excited, which has not been achieved in nanostructured BaTiO3 ceramics.
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77.80.B- Phase transitions and Curie point
73.61.Ng Insulators
77.84.Ek Niobates and tantalates
77.84.Cg PZT ceramics and other titanates
77.80.Fm Switching phenomena
81.20.Ev Powder processing: powder metallurgy, compaction, sintering, mechanical alloying, and granulation

Effects of rare earth manganites on structural, ferroelectric, and magnetic properties of BiFeO3 thin films

A. Lahmar, S. Habouti, M. Dietze, C.-H. Solterbeck, and M. Es-Souni

Appl. Phys. Lett. 94, 012903 (2009); http://dx.doi.org/10.1063/1.3064954 (3 pages) | Cited 28 times

Online Publication Date: 6 January 2009

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The results of structural studies of pure-phase perovskite thin films of BiFeO3–10% RMnO3 (R = La, Eu, Gd, Tb, and Dy) are presented. Raman scattering studies show line broadening similar to what is reported for RMnO3; they were attributed to Jahn–Teller distortion and orthorhombic structural change. Evidence of an anomaly of the orthorhombic distortion at GdMnO3 could be obtained. Interestingly the addition of GdMnO3 leads to a substantial increase in magnetization, combined with moderate ferroelectric polarization. All other compositions are characterized by higher ferroelectric polarization but almost no magnetization.
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77.55.-g Dielectric thin films
77.80.-e Ferroelectricity and antiferroelectricity
77.84.Bw Elements, oxides, nitrides, borides, carbides, chalcogenides, etc.
78.30.Hv Other nonmetallic inorganics
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
77.22.Ej Polarization and depolarization

Significant influence of film thickness on the percolation threshold of multiwall carbon nanotube/low density polyethylene composite films

M. Fu, Y. Yu, J. J. Xie, L. P. Wang, M. Y. Fan, S. L. Jiang, and Y. K. Zeng

Appl. Phys. Lett. 94, 012904 (2009); http://dx.doi.org/10.1063/1.3056055 (3 pages) | Cited 5 times

Online Publication Date: 6 January 2009

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A series of multiwall carbon nanotube/low density polyethylene composite films with different thicknesses and different carbon nanotube volume fractions was prepared and studied. The result showed an interesting phenomenon which has not been reported before: when the thickness was reduced to the length range of the carbon nanotube filler, it could remarkably affect the percolation threshold of the composite films. Classical theories have been introduced to describe the phenomenon. This result could have significance in future applications of percolative composite thin/thick films.
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73.61.Wp Fullerenes and related materials
77.22.Ch Permittivity (dielectric function)
68.55.jd Thickness
61.48.De Structure of carbon nanotubes, boron nanotubes, and other related systems
72.80.Rj Fullerenes and related materials
72.80.Tm Composite materials

On dielectric breakdown in silicon-rich silicon nitride thin films

S. Habermehl, R. T. Apodaca, and R. J. Kaplar

Appl. Phys. Lett. 94, 012905 (2009); http://dx.doi.org/10.1063/1.3065477 (3 pages) | Cited 2 times

Online Publication Date: 7 January 2009

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Observations of dielectric breakdown in Si-rich silicon nitride indicate that it is initiated by threshold field trap ionization. The films exhibit the charge transport mechanism of Poole–Frenkel emission with a compositionally dependent ionization potential ranging from 0.58 to 1.22 eV. Similar to silicon oxynitride, the barrier lowering energy at the point of dielectric breakdown is correlated with within ∼ 2kT of the ionization potential, thus revealing a dual role for bulk traps in the film: regulating charge transport and retarding hot electron generation. Additionally, a semiempirical expression is developed that accurately predicts the compositional dependence of the breakdown field.
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77.22.Jp Dielectric breakdown and space-charge effects
73.50.Fq High-field and nonlinear effects
73.61.Ng Insulators
77.55.-g Dielectric thin films
73.50.Gr Charge carriers: generation, recombination, lifetime, trapping, mean free paths

Unambiguous evidence for magnetoelectric coupling of multiferroic origin in 0.73BiFeO3–0.27PbTiO3

Shuvrajyoti Bhattacharjee, V. Pandey, R. K. Kotnala, and Dhananjai Pandey

Appl. Phys. Lett. 94, 012906 (2009); http://dx.doi.org/10.1063/1.3068000 (3 pages) | Cited 13 times

Online Publication Date: 9 January 2009

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Magnetization, frequency dependent dielectric, and structural studies on 0.73BiFeO3–0.27PbTiO3 in the temperature range from 300 to 600 K reveal anomalies in the unit cell parameters and the intrinsic value of the dielectric constant, free from space charge contributions, at the antiferromagnetic transition temperature (TN). Our results provide unambiguous confirmation of magnetoelectric coupling of multiferroic origin at TN and evidence for monoclinic distortion of the ferroelectric phase.
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75.80.+q Magnetomechanical effects, magnetostriction
77.80.B- Phase transitions and Curie point
61.66.Fn Inorganic compounds
77.22.Ch Permittivity (dielectric function)
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)
75.50.Ee Antiferromagnetics

A first-principles study of enhanced dielectric responses in Ti and Ce doped HfO2

Gargi Dutta

Appl. Phys. Lett. 94, 012907 (2009); http://dx.doi.org/10.1063/1.3063126 (3 pages) | Cited 12 times

Online Publication Date: 9 January 2009

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In this letter, the dielectric response in Ti and Ce doped hafnia (HfO2) has been investigated by density functional theory calculations based on pseudopotentials, plane wave basis, and local density approximation. It is found that Ti doped samples give greater dielectric response than Ce doped HfO2, with Hf0.5Ti0.5O2 having the highest response. The Born effective charges on atoms and infrared-active phonon modes have been studied; soft phonon modes cause enhancement in the responses. The materials remain insulating upon doping of HfO2 and are of potential importance for applications as gate oxide.
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77.22.Ch Permittivity (dielectric function)
71.15.Mb Density functional theory, local density approximation, gradient and other corrections
71.15.Dx Computational methodology (Brillouin zone sampling, iterative diagonalization, pseudopotential construction)
77.55.-g Dielectric thin films
63.20.dk First-principles theory
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