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1 May 2012

Volume 111, Issue 9, Articles (09xxxx)

Issue Cover Spotlight Figure

J. Appl. Phys. 111, 093103 (2012); http://dx.doi.org/10.1063/1.4709385 (8 pages)

Ani Khachatrian, Joseph S. Melinger, and Syed B. Qadri
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back to top Dielectrics and Ferroelectricity

Retention behavior of composites consisting of ferroelectric particles embedded in dielectric polymers

T. Lehnert, J. Adam, and M. Veith

J. Appl. Phys. 111, 094101 (2012); http://dx.doi.org/10.1063/1.4709747 (5 pages)

Online Publication Date: 4 May 2012

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As ferroelectric ceramic/polymer composites may offer the possibility to lower the operating voltage of state of the art polymer ferroelectric memories, the retention behavior of these composites needs to be studied. This work presents for the first time the polarization decay of a ceramic/polymer composite memory and discusses some influencing parameters. The existence of a depolarization field in such particulate structures, which is responsible for the polarization loss is demonstrated by finite element simulations, and first theoretical predictions are generated how to reduce this depolarizing field. Interestingly, first results from the experimental approach of varying the ionic concentration in the surrounding medium of the particles contradict these theoretical assumptions.
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77.22.Ej Polarization and depolarization
77.22.Gm Dielectric loss and relaxation
77.80.-e Ferroelectricity and antiferroelectricity
85.50.Gk Non-volatile ferroelectric memories
77.84.Cg PZT ceramics and other titanates

Specific heat of ferroelectric Pb(Zr1−xTix)O3 ceramics across the morphotropic phase boundary

S. B. Lang, W. M. Zhu, and Z.-G. Ye

J. Appl. Phys. 111, 094102 (2012); http://dx.doi.org/10.1063/1.4712633 (5 pages) | Cited 1 time

Online Publication Date: 9 May 2012

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Ferroelectric ceramic materials have a wide range of applications because of their piezoelectric and pyroelectric properties. One of their most important physical properties is the specific heat. In this study, the specific heats of a series of Pb(Zr1−xTix)O3 (x = 0.41 to 0.48) (PZT) compositions in the vicinity of and across the morphotropic phase boundary (MPB) were measured and analyzed. The temperature range was from 1.8 to 300 K. It is believed that these are the lowest temperature specific heat measurements ever made on PZT. Absolute entropy and enthalpy were computed from the specific heat data. Differences between the specific heats of the different compositions were very small. However, the calculated Debye temperatures were slightly different. The composition with the highest Debye temperature (x = 0.47, ΘD = 274 K) was within the morphotropic phase boundary. The results are useful in computing design parameters for technical devices.
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77.84.Cg PZT ceramics and other titanates
77.70.+a Pyroelectric and electrocaloric effects
77.80.Dj Domain structure; hysteresis
65.40.Ba Heat capacity

Low temperature studies of surface plasmon polaritons in silver films

M. Mayy, G. Zhu, E. Mayy, A. Webb, and M. A. Noginov

J. Appl. Phys. 111, 094103 (2012); http://dx.doi.org/10.1063/1.4709751 (3 pages) | Cited 1 time

Online Publication Date: 9 May 2012

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We have studied propagation of surface plasmon polaritons at cryogenic temperatures and found the temperature-dependent optical loss reduction to be modest. Large temperature-independent components of the dc resistivity and the imaginary part of the dielectric constant at optical frequency are due to scattering on bulk and surface defects rather than on phonons. This suggests that the quality of metal should be improved first, after which a further improvement can be sought through the reduction of temperature.
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73.20.Mf Collective excitations (including excitons, polarons, plasmons and other charge-density excitations)
77.22.Ch Permittivity (dielectric function)
68.55.-a Thin film structure and morphology
71.36.+c Polaritons (including photon-phonon and photon-magnon interactions)

Conduction mechanism of resistive switching films in MgO memory devices

Fu-Chien Chiu, Wen-Chieh Shih, and Jun-Jea Feng

J. Appl. Phys. 111, 094104 (2012); http://dx.doi.org/10.1063/1.4712628 (5 pages)

Online Publication Date: 10 May 2012

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In this work, nonpolar resistance switching behavior was demonstrated in Pt/MgO/Pt structure. The resistance ratio of high resistance state (HRS) and low resistance state (LRS) is about on the order of 105 for the compliance current (Icomp) of 1 mA at 300 K. Using enough Icomp (≥0.5 mA) during SET processes, the LRS resistances reach a minimum of about 102–103 Ω and the RESET currents reach a maximum of about 10−4–10−3 A. Experimental results indicate that the conduction mechanism in MgO films is dominated by the hopping conduction and the Ohmic conduction in HRS and LRS, respectively. Therefore, the electrical parameters of trap energy level, trap spacing, Fermi level, electron mobility, and effective density of states in conduction band in MgO films were obtained.
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84.30.Sk Pulse and digital circuits

Electromechanical strain in Bi(Zn1/2Ti1/2)O3–(Bi1/2Na1/2)TiO3–(Bi1/2K1/2)TiO3 solid solutions

Eric A. Patterson, David P. Cann, Jan Pokorny, and Ian M. Reaney

J. Appl. Phys. 111, 094105 (2012); http://dx.doi.org/10.1063/1.4714346 (5 pages) | Cited 5 times

Online Publication Date: 10 May 2012

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Solid solutions ceramics of the Bi(Zn0.5Ti0.5)O3–(Bi0.5K0.5)TiO3–(Bi0.5Na0.5)TiO3 ternary system for <20 mol. % BZT were created and confirmed to be single phase using x-ray diffraction. The dielectric dispersion showed decreasing Tmax of the dielectric spectrum with a broadening of the transition with increasing BZT content. At 2.5BZT–40BKT–57.5BNT, a secondary transition commonly observed for morphotropic phase boundary (MPB) BNT–BKT was observed. The ferroelectric behavior of the system was characterized by a transition where the polarization hysteresis showed a severe pinching effect on remanent polarization (20.8 μC/cm2 at 2.5% BZT) as BZT contents was increased (Pr = 2.3 μC/cm2 at 20% BZT). Similarly, as the temperature increased to 175 °C, the remanent polarization of the 2.5% BZT composition significantly reduced to 2.1 μC/cm2. The onset of this transition corresponds to the lower temperature frequency dispersion observed in the dielectric spectrum. The strain hysteresis experienced analogous transition to the polarization, with a change in shape from typical ferroelectric butterfly to a complete loss of negative strain as BZT concentration increased. Maximum strain values of 0.33% were observed at 5-40-55 accompanied by a large d33* = 547pm/V.
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77.80.bn Strain and interface effects
81.05.Je Ceramics and refractories (including borides, carbides, hydrides, nitrides, oxides, and silicides)
77.84.Cg PZT ceramics and other titanates
77.80.Dj Domain structure; hysteresis
77.22.Ej Polarization and depolarization
77.22.Ch Permittivity (dielectric function)

Electric-field induced phase transitions of dielectric colloids: Impact of multiparticle effects

Jeffery A. Wood and Aristides Docoslis

J. Appl. Phys. 111, 094106 (2012); http://dx.doi.org/10.1063/1.4714550 (10 pages) | Cited 1 time

Online Publication Date: 10 May 2012

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The thermodynamic framework for predicting the electric-field induced fluid like-solid like phase transition of dielectric colloids developed by Khusid and Acrivos [Phys. Rev. E. 54, 5428 (1996)] is extended to examine the impact of multiscattering/multiparticle effects on the resulting phase diagrams. This was accomplished using effective permittivity models suitable both over the entire composition region for hard spheres (0 ≤ c<cmax) and for multiple types of solid packing structures (random close-packed structure, FCC, BCC). The Sihvola-Kong model and the self-consistent permittivity model of Sen et al. [Geophysics 46, 781 (1981)] were used to generate the coexistence (slow phase transition) and spinodal (rapid phase transition) boundaries for the system and compared to assuming Maxwell-Garnett permittivity. It was found that for larger dielectric contrasts between medium and particle that the impact of accounting for multiscattering effects increased and that there was a significant shift in the resulting phase diagrams. Results obtained for model colloidal systems of silica-dimethylsulfoxide and silica-isopropanol showed that critical electric field strength required for phase transitions could rise by up to approximately 20% when considering multiparticle effects versus the isolated dipole case. The impact of multiparticle effects on the phase diagrams was not only limited purely to the direct effect of volume fraction on permittivity and particle dipoles but also on the curvature of the volume fraction dependence. This work stresses the importance of accounting for particle effects on the polarization of colloidal suspensions, which has large implications for predicting the behavior of electrorheological fluids and other electric-field driven phenomena.
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82.70.Dd Colloids
77.22.Ch Permittivity (dielectric function)
82.70.Kj Emulsions and suspensions
83.80.Hj Suspensions, dispersions, pastes, slurries, colloids
47.57.jd Electrokinetic effects
64.75.Xc Phase separation and segregation in colloidal systems

Performance of dissipative dielectric elastomer generators

Choon Chiang Foo, Soo Jin Adrian Koh, Christoph Keplinger, Rainer Kaltseis, Siegfried Bauer, and Zhigang Suo

J. Appl. Phys. 111, 094107 (2012); http://dx.doi.org/10.1063/1.4714557 (9 pages)

Online Publication Date: 10 May 2012

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Dielectric elastomer generators are high-energy-density electromechanical transducers. Their performance is affected by dissipative losses. This paper presents a theoretical analysis of a dielectric elastomer generator with two dissipative processes: viscoelasticity and current leakage. Conversion cycles are shown to attain steady-state after several cycles. Performance parameters such as electrical energy generated per cycle, average power, and mechanical to electrical energy conversion efficiency are introduced. Trade-offs between large electrical energy and power output and poor conversion efficiency are discussed. Excessive current leakage results in negative efficiency—the dielectric elastomer generator wastes energy instead of generating it. The general framework developed in this paper helps in the design and assessment of conversion cycles for dissipative dielectric elastomer generators.
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89.20.Kk Engineering
07.07.Mp Transducers
07.07.Tw Servo and control equipment; robots

First-principles study of intrinsic point defects in hexagonal barium titanate

J. A. Dawson, J. H. Harding, H. Chen, and D. C. Sinclair

J. Appl. Phys. 111, 094108 (2012); http://dx.doi.org/10.1063/1.4711099 (8 pages)

Online Publication Date: 10 May 2012

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Density functional theory (DFT) calculations have been used to study the nature of intrinsic defects in the hexagonal polymorph of barium titanate. Defect formation energies are derived for multiple charge states, and due consideration is given to finite-size effects (elastic and electrostatic) and the band gap error in defective cells. Correct treatment of the chemical potential of atomic oxygen means that it is possible to circumvent the usual errors associated with the inaccuracy of DFT calculations on the oxygen dimer. Results confirm that both mono- and di-vacancies exist in their nominal charge states over the majority of the band gap. Oxygen vacancies are found to dominate the system in metal-rich conditions with face sharing oxygen vacancies being preferred over corner sharing oxygen vacancies. In oxygen-rich conditions, the dominant vacancy found depends on the Fermi level. Binding energies also show the preference for metal-oxygen di-vacancy formation. Calculated equilibrium concentrations of vacancies in the system are presented for numerous temperatures. Comparisons are drawn with the cubic polymorph as well as with previous potential-based simulations and experimental results.
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61.72.jd Vacancies
71.20.Ps Other inorganic compounds
71.15.Nc Total energy and cohesive energy calculations
65.40.G- Other thermodynamical quantities
81.40.Jj Elasticity and anelasticity, stress-strain relations
71.15.Mb Density functional theory, local density approximation, gradient and other corrections

Heterophase states and domain effects in solid solutions of (1 − x)BiFeO3 − xPbTiO3

V. Yu. Topolov

J. Appl. Phys. 111, 094109 (2012); http://dx.doi.org/10.1063/1.4712631 (8 pages) | Cited 1 time

Online Publication Date: 11 May 2012

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Examples of heterophase states in multiferroic solid solutions of (1 − x)BiFeO3 − xPbTiO3 with the perovskite-type structure are studied taking into account the features of elastic matching of polydomain (twinned) ferroelectric phases near the morphotropic phase boundary and in a wide temperature range. Conditions for the complete stress relief are examined in the heterophase states P4mm–P4mm and P4mm–Cc to interpret variations of the phase content [S. Bhattacharjee et al., Phys. Rev. B 84, 104116 (2011)] [S. Bhattacharjee and D. Pandey, J. Appl. Phys. 110, 084105 (2011)] in (1−x)BiFeO3−xPbTiO3. The key role of some 90° domain types of the low-temperature ferroelectric P4mm phase in the stress relief at the phase coexistence is emphasized. An agreement between the evaluated and experimental data on the volume fraction of the low-temperature P4mm phase in heterophase samples is observed.
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75.85.+t Magnetoelectric effects, multiferroics
77.84.Cg PZT ceramics and other titanates

Stability of nano-scale ferroelectric domains in a LiNbO3 single crystal: The role of surface energy and polar molecule adsorption

X. Sun, Y. J. Su, X. Li, K. W. Gao, and L. J. Qiao

J. Appl. Phys. 111, 094110 (2012); http://dx.doi.org/10.1063/1.4711098 (6 pages) | Cited 1 time

Online Publication Date: 11 May 2012

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The stability of nano-scale ferroelectric domains in a LiNbO3 single crystal under varied atmospheric humidity levels was studied using piezoelectric force microscopy. Experimental results showed that the nano-scale domains fabricated by the tip field of the atomic force microscope changed as the environmental humidity changed; the c− domains expanded or shrank with increases or decreases in the environmental humidity (that is, with the amount of adsorbed H2O molecules on the domain surface), while the c+ domains transformed in the opposite sense. The surface energy of the domains is responsible for these transformations.
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77.80.Dj Domain structure; hysteresis
68.35.Md Surface thermodynamics, surface energies
68.43.Mn Adsorption kinetics
81.16.-c Methods of micro- and nanofabrication and processing
61.46.-w Structure of nanoscale materials
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