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11 Apr 2011

Volume 98, Issue 15, Articles (15xxxx)

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Appl. Phys. Lett. 98, 153103 (2011); http://dx.doi.org/10.1063/1.3555342 (3 pages)

Hsin-Yu Wu and Brian T. Cunningham
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Monoclinic crystal structure of polycrystalline Na0.5Bi0.5TiO3

Elena Aksel, Jennifer S. Forrester, Jacob L. Jones, Pam A. Thomas, Katharine Page, and Matthew R. Suchomel

Appl. Phys. Lett. 98, 152901 (2011); http://dx.doi.org/10.1063/1.3573826 (3 pages) | Cited 29 times

Online Publication Date: 11 April 2011

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Bismuth-based ferroelectric ceramics are currently under intense investigation for their potential as Pb-free alternatives to lead zirconate titanate-based piezoelectrics. Na0.5Bi0.5TiO3 (NBT), one of the widely studied compositions, has been assumed thus far to exhibit the rhombohedral space group R3c at room temperature. High-resolution powder x-ray diffraction patterns, however, reveal peak splitting in the room temperature phase that evidence the true structure as monoclinic with space group Cc. This peak splitting and Cc space group is only revealed in sintered powders; calcined powders are equally fit to an R3c model because microstructural contributions to peak broadening obscure the peak splitting.
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61.66.Fn Inorganic compounds
77.80.-e Ferroelectricity and antiferroelectricity
81.20.Ev Powder processing: powder metallurgy, compaction, sintering, mechanical alloying, and granulation
81.05.Je Ceramics and refractories (including borides, carbides, hydrides, nitrides, oxides, and silicides)

Electrical reliability and leakage mechanisms in highly resistive multiferroic La0.1Bi0.9FeO3 ceramics

S. Y. Wang, Xue Qiu, J. Gao, Yu Feng, W. N. Su, J. X. Zheng, D. S. Yu, and D. J. Li

Appl. Phys. Lett. 98, 152902 (2011); http://dx.doi.org/10.1063/1.3580604 (3 pages) | Cited 6 times

Online Publication Date: 13 April 2011

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Multiferroic La0.1Bi0.9FeO3 (LBFO) ceramics with high resistivity were synthesized by using a modified rapid thermal process. The LBFO ceramics show very low leakage and low dielectric loss. Well saturated ferroelectric hysteresis loops and polarization switching currents have been observed. For a maximum applied electric field of 145 kV/cm, the remanent polarization is 17.8 μC/cm2 and the coercive filed is 75 kV/cm. The dominant conduction mechanism in the LBFO ceramics has been found to be the space-charge-limited current mechanism rather than the thermal excitation mechanism. Electrical reliability related to the fatigue and polarization retention of the LBFO ceramics has also been discussed with the leakage mechanisms.
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77.80.Dj Domain structure; hysteresis
77.22.Gm Dielectric loss and relaxation
77.22.Ej Polarization and depolarization
81.40.Np Fatigue, corrosion fatigue, embrittlement, cracking, fracture, and failure
77.80.Fm Switching phenomena
77.84.-s Dielectric, piezoelectric, ferroelectric, and antiferroelectric materials

Measurement of oxygen diffusion in nanometer scale HfO2 gate dielectric films

Sufi Zafar, Hemanth Jagannathan, Lisa F. Edge, and Devendra Gupta

Appl. Phys. Lett. 98, 152903 (2011); http://dx.doi.org/10.1063/1.3579256 (3 pages) | Cited 2 times

Online Publication Date: 14 April 2011

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Diffusion of oxygen ions in thin (≲40 Å) HfO2 gate dielectric films is measured using transient gate currents. The diffusion coefficient is estimated to be ∼ 1×10−14 cm2/s at room temperature, and is observed to be thermally activated with an activation energy of ∼ 0.52 eV for nanometer scale HfO2 films. The diffusion results are shown to be consistent with those for positively charged oxygen vacancies in bulk samples of similar oxides, and first principle calculation results for oxygen vacancy diffusion in thin HfO2 films. Thus, we demonstrate a method for measuring oxygen diffusion in thin HfO2 films where diffusion measurements by the conventional techniques have been elusive.
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77.55.-g Dielectric thin films
66.30.Lw Diffusion of other defects
61.72.jd Vacancies
77.84.Bw Elements, oxides, nitrides, borides, carbides, chalcogenides, etc.

Effects of porosity on dielectric and piezoelectric properties of porous lead zirconate titanate ceramics

An-Kun Yang, Chang-An Wang, Rui Guo, and Yong Huang

Appl. Phys. Lett. 98, 152904 (2011); http://dx.doi.org/10.1063/1.3578196 (3 pages) | Cited 5 times

Online Publication Date: 14 April 2011

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We report porous lead zirconate titanate ceramics fabricated by tert-butyl alcohol-based gel-casting process which show a very high thickness electromechanical coupling coefficient (0.77), high hydrostatic figure of merit (9594×10−15 m2/N), and low acoustic impedance (3.7 Mrayls). We show that the porosity effectively affects the performance of the samples in two ways: (1) a higher porosity simplifies the resonance behavior, leading to more efficient energy transduction; (2) its replacement of active ceramic phase leads to low relative permittivity, high hydrostatic figure of merit, and low acoustic impedance. It was confirmed the properties could be tailored by controlling the porosity.
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77.22.Ch Permittivity (dielectric function)
77.65.-j Piezoelectricity and electromechanical effects
81.05.Je Ceramics and refractories (including borides, carbides, hydrides, nitrides, oxides, and silicides)
81.05.Rm Porous materials; granular materials
61.43.Gt Powders, porous materials
82.70.Gg Gels and sols
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