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22 Oct 2001

Volume 79, Issue 17, pp. 2681-2850

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Crystal and electronic structures of Bi4−xLaxTi3O12 ferroelectric materials

Y. Shimakawa, Y. Kubo, Y. Tauchi, H. Asano, T. Kamiyama, F. Izumi, and Z. Hiroi

Appl. Phys. Lett. 79, 2791 (2001); http://dx.doi.org/10.1063/1.1410877 (3 pages) | Cited 149 times

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The crystal structures of Bi4Ti3O12 and Bi3.25La0.75Ti3O12 were refined by neutron powder diffraction. Large structural distortions were revealed, and ferroelectric polarizations along the a and c axes were calculated from the displacements of the constituent ions. In Bi3.25La0.75Ti3O12, La atoms substitute for Bi atoms in a perovskite-type unit only, and the substitution causes less distortion of the structure, resulting in smaller spontaneous polarization and lower ferroelectric Curie temperature. Electronic-structure calculations revealed that covalent interaction, which originates from the strong hybridization between Ti 3d and O 2p orbitals, plays an important role in the structural distortion and ferroelectricity of the materials. Changes in ceramic-sample density with sintering temperature give information concerning device fabrication temperature; that is, substituting La for Bi atoms appears to “increase” the synthesis temperature of the Bi4Ti3O12 and Bi3.25La0.75Ti3O12 systems. © 2001 American Institute of Physics.
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77.84.Ek Niobates and tantalates
77.84.Cg PZT ceramics and other titanates
61.66.Fn Inorganic compounds
77.80.B- Phase transitions and Curie point
71.20.Ps Other inorganic compounds
81.05.Je Ceramics and refractories (including borides, carbides, hydrides, nitrides, oxides, and silicides)
81.20.Ev Powder processing: powder metallurgy, compaction, sintering, mechanical alloying, and granulation
77.22.Ej Polarization and depolarization

Ultrasonic characterization of poling in lead zirconate titanate ceramics

James Friend, Eric Jamieson, Marvin Pennell, and Wayne Huebner

Appl. Phys. Lett. 79, 2794 (2001); http://dx.doi.org/10.1063/1.1412595 (3 pages) | Cited 3 times

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A method for measuring the spatial variation of the macroscopic poling state of a piezoelectric material using an ultrasonic transducer is described. The relatively simple method clearly indicates the distribution of poling within the material, demonstrated by the testing of a collection of partially poled lead zirconate titanate samples. © 2001 American Institute of Physics.
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77.65.-j Piezoelectricity and electromechanical effects
77.84.Ek Niobates and tantalates
77.84.Cg PZT ceramics and other titanates
77.22.Ej Polarization and depolarization
62.65.+k Acoustical properties of solids

Photovoltaic response and dielectric properties of epitaxial anatase-TiO2 films grown on conductive La0.5Sr0.5CoO3 electrodes

B. H. Park, L. S. Li, B. J. Gibbons, J. Y. Huang, and Q. X. Jia

Appl. Phys. Lett. 79, 2797 (2001); http://dx.doi.org/10.1063/1.1412822 (3 pages) | Cited 13 times

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We have grown epitaxial anatase-TiO2 (001) films on La0.5Sr0.5CoO3 (001) bottom electrodes using pulsed-laser deposition. The small lattice mismatch (0.5%) between the anatase-TiO2 and the La0.5Sr0.5CoO3 makes it possible to grow anatase-TiO2 films with excellent crystallinity on conductive metal oxides. The photovoltaic properties of the epitaxial anatase-TiO2 on the La0.5Sr0.5CoO3 were characterized using a Kelvin probe. The optical band-gap energy was found to be 3.05 eV. The dielectric properties of the epitaxial anatase-TiO2 films were characterized using a capacitor structure of Au/anatase-TiO2/La0.5Sr0.5CoO3 on a LaAlO3 substrate. The dielectric dispersion exhibited a power-law dependence, and the dielectric constant measured at room temperature and 1 MHz was 38. © 2001 American Institute of Physics.
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73.61.Le Other inorganic semiconductors
81.15.Fg Pulsed laser ablation deposition
77.22.Ch Permittivity (dielectric function)
73.50.Pz Photoconduction and photovoltaic effects
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
78.66.Li Other semiconductors

Field-induced sharp ferroelectric phase transition in Sr0.66Ba0.34Nb2O6 relaxor ferroelectric

I. A. Santos, D. Garcia, J. A. Eiras, E. R. Manoel, and A. C. Hernandes

Appl. Phys. Lett. 79, 2800 (2001); http://dx.doi.org/10.1063/1.1413727 (3 pages) | Cited 8 times

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Field-induced sharp ferroelectric phase transition was observed in Sr0.66Ba0.34Nb2O6 single crystals. The peaks of the real and imaginary parts of dielectric permittivity arise upon cooling under weak dc bias electric fields and subsequently heating under zero fields or upon cooling under zero fields and subsequently heating under weak electric fields. The applied electric field cancels the random fields that destroy the phase transition and give rise to low temperature domain state if E = 0. These results strongly suggest that the SBN system belongs to the random field Ising universality class, a rare case among structural phase transitions. © 2001 American Institute of Physics.
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77.84.Ek Niobates and tantalates
77.84.Cg PZT ceramics and other titanates
77.80.B- Phase transitions and Curie point
77.22.Ch Permittivity (dielectric function)
77.22.Gm Dielectric loss and relaxation

Temperature dependence of gate currents in thin Ta2O5 and TiO2 films

Z. J. Luo, Xin Guo, T. P. Ma, and T. Tamagawa

Appl. Phys. Lett. 79, 2803 (2001); http://dx.doi.org/10.1063/1.1412823 (2 pages) | Cited 17 times

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This letter reports our study of the temperature dependence of gate currents in thin Ta2O5 and TiO2 films. The study was conducted (1) to study the conduction mechanisms and band alignments, and (2) to determine whether the gate leakage current is tolerable at high temperatures for either of these high-dielectric-constant (high-k) oxides. The I–V characteristics of these oxides were measured and analyzed over a wide temperature range from 25 to 400 °C. Currents in Ta2O5 samples exhibited stronger temperature dependence than those in TiO2 samples, especially at high fields, mainly due to a much smaller electron barrier height of Ta2O5 over Si (0.28 eV) than that of TiO2 over Si (0.9 eV). © 2001 American Institute of Physics.
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73.40.Qv Metal-insulator-semiconductor structures (including semiconductor-to-insulator)
73.61.Ng Insulators
84.32.Tt Capacitors

Control of domain structure of epitaxial PbZr0.2Ti0.8O3 thin films grown on vicinal (001) SrTiO3 substrates

V. Nagarajan, C. S. Ganpule, H. Li, L. Salamanca-Riba, A. L. Roytburd, E. D. Williams, and R. Ramesh

Appl. Phys. Lett. 79, 2805 (2001); http://dx.doi.org/10.1063/1.1402645 (3 pages) | Cited 10 times

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We have investigated the polydomain formation in 100–200-nm-thick PbZr0.2Ti0.8O3 epitaxial thin films on vicinally cut (100) oriented SrTiO3 substrates. Our results show that there is a preferential location of the nucleation of the a domains along the step edges of the underlying substrate. By piezo-response microscopy, we show that all a domains have their polarization aligned along the same direction. This result is in contrast to flat substrates where fourfold symmetry of a domains is observed. We observe that the critical thickness for a domain formation is much lower than that for PbZr0.2Ti0.8O3 films grown on flat substrates. We have developed a model based on minimization of elastic energy to describe the effect of localized stresses at step edges on the formation of a domains in the ferroelectric layer. © 2001 American Institute of Physics.
Show PACS
77.55.-g Dielectric thin films
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)
77.80.Dj Domain structure; hysteresis
68.55.-a Thin film structure and morphology
68.60.Bs Mechanical and acoustical properties
77.22.Ej Polarization and depolarization
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