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1 Mar 2005

Volume 97, Issue 5, Articles (05xxxx)

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Dopant site selectivity in BaCe0.85M0.15O3-δ by extended x-ray absorption fine structure

J. Wu, S. M. Webb, S. Brennan, and S. M. Haile

J. Appl. Phys. 97, 054101 (2005); http://dx.doi.org/10.1063/1.1846946 (7 pages) | Cited 10 times

Online Publication Date: 10 February 2005

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Rare earth doped BaCeO3 has been widely investigated as a proton conducting material. Trivalent dopants are generally assumed to fully occupy the Ce4+-site, and thereby introduce oxygen vacancies into the perovskite structure. Recent studies indicate the possibility of partial dopant incorporation onto the Ba2+-site concomitant with BaO evaporation, reducing the oxygen vacancy content. Because proton incorporation requires, as a first step, the generation of oxygen vacancies such dopant partitioning is detrimental to protonic conductivity. A quantitative Extended X-ray Absorption Fine Structure (EXAFS) study of BaCe0.85M0.15O3-δ(M = Yb,Gd) is presented here along with complementary x-ray powder diffraction and electron probe chemical analyses. The EXAFS results demonstrate that as much as 4.6% of the ytterbium and 7.2% of the gadolinium intended for incorporation onto the Ce site, in fact, resides on the Ba site. The results are in qualitative agreement with the diffraction and chemical analyses, which additionally show an even greater extent of Nd incorporation on the Ba site.
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61.72.S- Impurities in crystals
61.72.J- Point defects and defect clusters
66.30.H- Self-diffusion and ionic conduction in nonmetals
82.80.Pv Electron spectroscopy (X-ray photoelectron (XPS), Auger electron spectroscopy (AES), etc.)
78.70.Dm X-ray absorption spectra
81.70.Jb Chemical composition analysis, chemical depth and dopant profiling

Effects of donor concentration on the electrical properties of Nb-doped BaTiO3 thin films

Lifeng Liu, Haizhong Guo, Huibin Lü, Shouyu Dai, Bolin Cheng, and Zhenghao Chen

J. Appl. Phys. 97, 054102 (2005); http://dx.doi.org/10.1063/1.1858056 (5 pages) | Cited 5 times

Online Publication Date: 10 February 2005

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Thin films of BaNbxTi1−xO3 (0<x ⩽ 0.5) were epitaxially grown on MgO substrates by laser molecular beam epitaxy. The thin films undergo tetragonal to cubic and semiconductor to metal transitions with Nb concentrations as shown by x-ray diffraction and electrical resistivity measurements. Room temperature resistivities are found to decrease monotonically with increasing Nb concentration and range from 101 to 10−4 Ω cm. The fact that the temperature dependence of resistivity of the thin films can be fitted well using a small polaron model reveals the polaronic nature of the charge carriers in the thin films. This conclusion is further confirmed by the existence of localized states within the band gap of BaTiO3 as revealed by synchrotron radiation-based ultraviolet photoelectron spectroscopy.
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61.72.S- Impurities in crystals
73.61.Ng Insulators
73.20.Mf Collective excitations (including excitons, polarons, plasmons and other charge-density excitations)
73.50.Jt Galvanomagnetic and other magnetotransport effects (including thermomagnetic effects)
72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping
71.30.+h Metal-insulator transitions and other electronic transitions
73.20.At Surface states, band structure, electron density of states
81.30.Hd Constant-composition solid-solid phase transformations: polymorphic, massive, and order-disorder
64.70.K- Solid-solid transitions
79.60.Bm Clean metal, semiconductor, and insulator surfaces
79.60.Dp Adsorbed layers and thin films
68.55.A- Nucleation and growth

Domain engineered states over various length scales in (001)-oriented Pb(Mg1/3Nb2/3)O3-x%PbTiO3 crystals: Electrical history dependence of hierarchal domains

Feiming Bai, Jiefang Li, and D. Viehland

J. Appl. Phys. 97, 054103 (2005); http://dx.doi.org/10.1063/1.1855392 (7 pages) | Cited 33 times

Online Publication Date: 11 February 2005

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The dependence of the domain structure on poling for (001)-oriented Pb(Mg1/3Nb2/3)O3-x%PbTiO3 crystals with x = 20, 30, 35, and 40 has been investigated by scanning force microscopy in the piezoresponse mode and by polarized optical microscopy. The results demonstrate a domain hierarchy on various length scales, ranging from nanometers to millimeters, which is notably dependent upon the electrical history of the specimen. The results provide important insights into the nature of the domain engineered state in these crystals.
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77.84.Ek Niobates and tantalates
77.84.Cg PZT ceramics and other titanates
77.80.Dj Domain structure; hysteresis
77.65.-j Piezoelectricity and electromechanical effects
68.37.Ps Atomic force microscopy (AFM)

Similarities in photoluminescence in hafnia and zirconia induced by ultraviolet photons

Toshihide Ito, Motohiro Maeda, Kazuhiko Nakamura, Hiromitsu Kato, and Yoshimichi Ohki

J. Appl. Phys. 97, 054104 (2005); http://dx.doi.org/10.1063/1.1856220 (7 pages) | Cited 25 times

Online Publication Date: 14 February 2005

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Photoluminescence (PL) spectra induced by ultraviolet photons were measured for amorphous hafnia and zirconia deposited by plasma-enhanced chemical-vapor deposition (PECVD), amorphous hafnia deposited by pulse laser deposition, and crystalline yttria-stabilized zirconia. Two kinds of samples were prepared for both hafnia and zirconia deposited by PECVD using different source alkoxides in different deposition chambers. A PL peak was observed around 2.8 eV similarly in all hafnia and zirconia samples, irrespective of the difference in crystallinity, oxygen deficiency, source alkoxide, deposition method, or the substrate material. The decay profile of this PL is also similar in all the samples. These facts clearly show that neither impurities, oxygen vacancy, nor defects at the interface between the sample and the substrate are responsible for the PL. It is a luminescence inherent in hafnia and zirconia and is most likely due to radiative recombination between localized states at the band tails. When the samples were annealed in oxygen, a new PL peak appeared around 4.2 eV in all the amorphous samples. Its decay profile is also in common with these samples. Vacuum-ultraviolet absorption measurements and PL excitation measurements indicate that the 4.2-eV PL is excited due to the interband absorption.
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77.84.Bw Elements, oxides, nitrides, borides, carbides, chalcogenides, etc.
78.66.Nk Insulators
78.55.Hx Other solid inorganic materials
81.40.Gh Other heat and thermomechanical treatments

Aging behavior in Ba0.7Sr0.3Ti0.97Zr0.03O ceramics

J. Portelles, S. Garcia, E. Martinez, O. Raymond, N. S. Almodovar, J. L. Heiras, and J. M. Siqueiros

J. Appl. Phys. 97, 054105 (2005); http://dx.doi.org/10.1063/1.1857055 (5 pages) | Cited 2 times

Online Publication Date: 14 February 2005

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The polarization aging behavior of the Ba0.7Sr0.3Ti0.97Zr0.03O3 ceramic that presents diffuse phase transition, was investigated at different temperatures. The aging of this system is explained by assuming the existence of two different relaxation regimes, one associated with rapidly relaxing polarized macroregions (τ1) and the other to long time relaxing polarized microregions (τ2). With these considerations, a modified expression to describe the aging behavior is proposed, leading to a good fit to the experimental measurements of the polarization. Hysteresis loop, permittivity, and dielectric loss measurements were performed on the samples to support the aging study.
Show PACS
77.84.Ek Niobates and tantalates
77.84.Cg PZT ceramics and other titanates
81.05.Je Ceramics and refractories (including borides, carbides, hydrides, nitrides, oxides, and silicides)
77.22.Ej Polarization and depolarization
81.40.Cd Solid solution hardening, precipitation hardening, and dispersion hardening; aging
77.22.Gm Dielectric loss and relaxation
77.22.Ch Permittivity (dielectric function)
77.80.Dj Domain structure; hysteresis
77.80.B- Phase transitions and Curie point
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