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24 Dec 2007

Volume 91, Issue 26, Articles (26xxxx)

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Appl. Phys. Lett. 91, 261106 (2007); http://dx.doi.org/10.1063/1.2825578 (3 pages)

W. M. Zhu, T. Zhong, A. Q. Liu, X. M. Zhang, and M. Yu
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Hydrogen in Si(100)–SiO2–HfO2 gate stacks: Relevant charge states and their location

Julien Godet, Peter Broqvist, and Alfredo Pasquarello

Appl. Phys. Lett. 91, 262901 (2007); http://dx.doi.org/10.1063/1.2828027 (3 pages) | Cited 11 times

Online Publication Date: 26 December 2007

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Using a density functional approach, we study the energetics of various charged hydrogen states in the Si(100)–SiO2–HfO2 gate stack. We describe the SiO2–HfO2 transition region through model structures of amorphous hafnium silicate HfxSi1−xO2 with different Hf contents x. Hydrogen is found to be amphoteric with a +/− charge transition level lying close to the Si conduction band minimum. This implies that protons are the most stable form of hydrogen for most electron chemical potentials in the Si band gap. Formation energies of the positively charged state across the Si(100)–SiO2–HfO2 stack indicate that protons mainly locate in the Si–SiO2 or SiO2–HfO2 transition regions.
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71.15.Mb Density functional theory, local density approximation, gradient and other corrections
71.20.Ps Other inorganic compounds
73.20.At Surface states, band structure, electron density of states

Analysis of crystallographic evolution in (Na,K)NbO3-based lead-free piezoceramics by x-ray diffraction

Ke Wang and Jing-Feng Li

Appl. Phys. Lett. 91, 262902 (2007); http://dx.doi.org/10.1063/1.2825280 (3 pages) | Cited 34 times

Online Publication Date: 28 December 2007

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The crystallographic structure of (Na,K)NbO3-based compounds and phase transitional behavior in (1−x)(K0.5Na0.5)NbO3–xLiNbO3 (x = 0, 3, 6, and 8 mol %) ceramics were accurately determined using high resolution x-ray diffraction (XRD). The phase transition between orthorhombic and tetragonal was distinctly characterized focusing on the XRD peak changes in {222} and {400} diffraction planes, by which lattice parameters of the perovskite type subcell, a, b, and c as well as angle β can be calculated. The discontinuous change in angle β at x = 6 mol % is located at the phase transitional region, where enhanced piezoelectric constant d33 = 215 pC/N was obtained. The present study provides a precise as well as simple method to investigate crystallographic structures in (Na,K)NbO3-based ceramics.
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61.66.Fn Inorganic compounds
81.30.Hd Constant-composition solid-solid phase transformations: polymorphic, massive, and order-disorder
77.84.Ek Niobates and tantalates
77.84.Cg PZT ceramics and other titanates
77.65.Bn Piezoelectric and electrostrictive constants

Investigation on switching kinetics in epitaxial Pb(Zr0.2Ti0.8)O3 ferroelectric thin films: Role of the 90° domain walls

Wei Li and Marin Alexe

Appl. Phys. Lett. 91, 262903 (2007); http://dx.doi.org/10.1063/1.2825414 (3 pages) | Cited 22 times

Online Publication Date: 28 December 2007

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Ferroelectric switching behavior of single-crystal-like epitaxial Pb(Zr0.2Ti0.8)O3 thin films with different densities of 90° domain walls was investigated under various applied fields. It was found that the saturated switchable polarization of about 170 μC/cm2 did not vary with applied field in the films with low density or no 90° domain walls and obeys Kolmogorov-Avrami-Ishibashi theory. The presence of the 90° domain walls inhibits the motion of 180° domain walls, contributing to the change of the switching kinetics to nucleation-limited-switching model.
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77.84.Ek Niobates and tantalates
77.84.Cg PZT ceramics and other titanates
77.80.Fm Switching phenomena
77.80.Dj Domain structure; hysteresis
77.55.-g Dielectric thin films
77.22.Ej Polarization and depolarization
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