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23 Jan 2012

Volume 100, Issue 4, Articles (04xxxx)

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Appl. Phys. Lett. 100, 041101 (2012); http://dx.doi.org/10.1063/1.3675885 (4 pages)

Seung Ho Choi and Young L. Kim
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Powering pacemakers from heartbeat vibrations using linear and nonlinear energy harvesters

M. Amin Karami and Daniel J. Inman

Appl. Phys. Lett. 100, 042901 (2012); http://dx.doi.org/10.1063/1.3679102 (4 pages) | Cited 9 times

Online Publication Date: 23 January 2012

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Linear and nonlinear piezoelectric devices are introduced to continuously recharge the batteries of the pacemakers by converting the vibrations from the heartbeats to electrical energy. The power requirement of a pacemaker is very low. However, after few years, patients require another surgical operation just to replace their pacemaker battery. Linear low frequency and nonlinear mono-stable and bi-stable energy harvesters are designed according to the especial signature of heart vibrations. The proposed energy harvesters are robust to variation of heart rate and can meet the power requirement of pacemakers.
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87.85.-d Biomedical engineering
84.60.-h Direct energy conversion and storage
87.19.Hh Cardiac dynamics

Origin of the enhanced polarization in La and Mg co-substituted BiFeO3 thin film during the fatigue process

Qingqing Ke, Amit Kumar, Xiaojie Lou, Kaiyang Zeng, and John Wang

Appl. Phys. Lett. 100, 042902 (2012); http://dx.doi.org/10.1063/1.3678636 (4 pages) | Cited 4 times

Online Publication Date: 25 January 2012

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We have studied the polarization fatigue of La and Mg co-substituted BiFeO3 thin film, where a polarization peak is observed during the fatigue process. The origin of such anomalous behavior is analyzed on the basis of the defect evolution using temperature-dependent impedance spectroscopy. It shows that the motion of oxygen vacancies (VO••) is associated with a lower energy barrier, accompanied by the injection of electrons into the film during the fatigue process. A qualitative model is proposed to explain the fatigue behavior, which involves the modification of the Schottky barrier upon the accumulation of VO•• at the metal-dielectric interface.
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77.22.Ej Polarization and depolarization
77.80.Fm Switching phenomena
61.72.jd Vacancies
77.55.Nv Multiferroic/magnetoelectric films
77.55.fp Other ferroelectric films
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Giant electro-mechanical energy conversion in [011] cut ferroelectric single crystals

Wen D. Dong, Peter Finkel, Ahmed Amin, and Christopher S. Lynch

Appl. Phys. Lett. 100, 042903 (2012); http://dx.doi.org/10.1063/1.3679644 (3 pages) | Cited 4 times

Online Publication Date: 26 January 2012

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Giant electro-mechanical energy conversion is demonstrated under a ferroelectric/ferroelectric phase transformation in [011] cut and poled lead titanate-based relaxor perovskite morphotropic single crystals. It is found that under mechanical pre-stress, a relatively small oscillatory stress drives the material reversibly between rhombohedral and orthorhombic phases with a remarkably high polarization and strain jump induced at zero bias electric field and room temperature. The measured electrical output per cycle is more than an order of magnitude larger than that reported for linear piezoelectric materials. Ideal thermodynamic cycles are presented for this electro-mechanical energy conversion followed by a presentation and discussion of the experimental data.
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77.80.B- Phase transitions and Curie point
77.80.Jk Relaxor ferroelectrics
77.84.Cg PZT ceramics and other titanates
77.22.Ej Polarization and depolarization

Relaxor ferroelectric behavior of BaMnO3 (2H) at room temperature

S. Satapathy, M. K. Singh, Pragya Pandit, and P. K. Gupta

Appl. Phys. Lett. 100, 042904 (2012); http://dx.doi.org/10.1063/1.3679176 (4 pages)

Online Publication Date: 27 January 2012

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Geometrically frustrated hexagonal BaMnO3 (2H) is an interesting material due to the presence of more than one ferroic order parameters. Although the material is well known, still there exists confusion on the crystal structure of this material at room temperature and its ferroelectric properties have not been explored. Here, we report noncentrosymmetric crystal structure and ferroelectric properties of BaMnO3 (2H) at room temperature. The dielectric diffusivity calculated from modified Curie-Weiss laws and non linear Vogel-Fulcher fittings implies weak relaxor characteristic of BaMnO3 (2H). The ferroelectric properties arise due to off centering of Mn4+ ion in unit cell and weak relaxor properties are attributed to the presence of a smaller amount of Mn3+ cations which creates disorder in 2H-BaMnO3.
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77.80.Jk Relaxor ferroelectrics
61.66.Fn Inorganic compounds
77.22.Ch Permittivity (dielectric function)
77.80.Dj Domain structure; hysteresis
77.84.Bw Elements, oxides, nitrides, borides, carbides, chalcogenides, etc.
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