Piezoresponse imaging and local characterization of ferroelectric domains in Pb(Zn1/3Nb2/3)O3–7%PbTiO3 single crystals

Ferroelectric domain structures of (001)‐oriented Pb(Zn_1/3Nb_2/3)O₃–7%PbTiO₃ (PZN‐7%PT) single crystals were visualized and characterized by piezoresponse force microscopy (PFM). Locally regular domain configurations are found to be possibly related to the stable macroscopic properties in the PZN‐7%PT single crystals. Nanoscale piezoresponse hysteresis loops measured by PFM tip revealed no evidence of local domain switching behavior in the PZN‐7%PT single crystal. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Light-Induced Domain Inversion in Mg-Doped near Stoichiometric Lithium Niobate Crystals

We investigate the influence of visible light on domain inversion in Mg-doped near stoichiometric lithium niobate crystals and find that the switching electric field decreases about 70% above a threshold light intensity. This effect helps us optically control domain switching and produce bulk domain structures on the micrometre scale. Finally, we introduce a model of photo-induced carriers to explain the origin of the reduction of switching electric field.     

Temperature-dependent ferroelectric and dielectric properties of Bi3.25La0.75Ti3O12 thin films

To investigate temperature-dependent ferroelectric and dielectric properties of ferroelectric films, Bi_3.25La_0.75Ti₃O₁₂ (BLT) thin films were prepared on Pt-coated silicon substrates by pulsed laser deposition. The ferroelectric and dielectric behaviors have been studied in a wide temperature range from 80 K to room temperature. The saturated polarization (P_sat) decreases with decreasing temperature and decreasing electric field, whereas remnant polarization (P_r) shows a more complex temperature dependence. These results, which can be well explained based on a temperature-dependent charged defects-domain wall interaction model, might be helpful for further understanding the domain switching behavior. Based on these results, an alternative way to investigate temperature-dependent ferroelectric fatigue is proposed and experimentally carried out. The measured fatigue rate is found to be linearly dependent on temperature, consistent with the report on Pb(Zr,Ti)O₃ films. Temperature-dependent dielectric measurements of the films further confirm the above explanation.     

Fabrication and electrical properties of sol-gel-derived Ba0.8Sr0.2TiO3 ferroelectric films from a 0.05-M spin-on solution

Barium strontium titanate (Ba_0.8Sr_0.2TiO₃) films with good ferroelectricity have been obtained by a developed sol-gel processing, using a 0.05-M spin-on solution. X-ray diffraction and Raman spectroscopy investigations showed that the Ba_0.8Sr_0.2TiO₃ film exhibited a tetragonal structure at room temperature. Field-emission scanning electron microscopy measurements revealed that large columnar grains with the size of 100 to 200 nm in the film were formed from the highly dilute spin-on solution with layer-by-layer homoepitaxy. Electrical measurements for the prepared Ba_0.8Sr_0.2TiO₃ film showed a remnant polarization of 3.5 μC/cm², a coercive field of 53 kV/cm, two distinctive phase transitions, lower dissipation factor, and good insulating properties. These results indicate the sol-gel-derived Ba_0.8Sr_0.2TiO₃ film from a 0.05-M solution is suitable for uncooled infrared detector applications. Received: 19 August 1999 / Accepted: 11 October 1999 / Published online: 1 March 2000     

Texture control and its impact on the properties of SrBi2Ta2O9 thin films prepared by pulsed laser deposition

SrBi₂Ta₂O₉ (SBT) ferroelectric thin films with different preferred orientations were deposited by pulsed laser deposition (PLD). Several methods have been developed to control the preferred orientation of SBT thin films. For SBT films deposited directly on Pt/TiO₂/SiO₂/Si substrates and in situ crystallized at the deposition temperature, the substrate temperature has a significant impact on the orientation and the remnant polarization (Pr) of the films; a higher substrate temperature benefits the formation of (115) texture and larger grain size. The films deposited on Pt/TiO₂/SiO₂/Si substrates at 830 °C are (115)-oriented and exhibit 2Pr of 6 μC/cm². (115)- and (200)-predominant films can be formed by using a La_0.85Sr_0.15CoO₃ (LSCO) buffer layer or by annealing amorphous SBT films deposited on Pt/TiO₂/SiO₂/Si substrates at 450 °C using rapid thermal annealing (RTA). These films exhibit good electric properties; 2Pr of the films are up to 12 μC/cm² and 17 μC/cm², respectively. The much larger 2Pr of the films deposited on the LSCO buffer layer and of the films obtained by RTA than 2Pr of the films deposited on Pt/TiO₂/SiO₂/Si substrates at 830 °C is attributed to a stronger (200) texture. Received: 30 January 2001 / Accepted: 30 May 2001 / Published online: 25 July 2001     

Dependence of high electric-field-induced strain on the composition and orientation of Pb(Mg1/3Nb2/3)O3-PbTiO3 crystals

Electric-field-induced strain behavior of (1−x)Pb(Mg_1/3Nb_2/3)O₃-xPbTiO₃ (PMNT) crystals with different orientations and compositions was investigated for use as electromechanical actuators. Crystallographically, high strains with low hysteresis were achieved for 〈001〉 oriented rhombohedral crystals (29%≤x≤31%) near a morphotropic phase boundary, rather than 〈110〉 and 〈111〉. Domain instability could explain inferior strain levels and large hysteresis for 〈110〉 and 〈111〉 oriented crystals. Ultrahigh strain levels up to 1.8% could be achieved for 〈001〉 oriented PMNT crystals, being related to an E-field induced phase transition. −2 kV/cm negative E-field can be applied to PMNT ferroelectric material with low hysteresis. High strain with low hysteresis makes PMNT crystals promising candidates for high performance solid-state actuators.     

Nonlinear optical and electrostatic force microscopy for ferroelectric polarization imaging

Second-harmonic generation (SHG)-based nonlinear optical microscopy is used for spatially resolved imaging of the polarization switching in lead zirconium titanate ferroelectric thin films. The local SHG hysteresis loops reveal a strong dependence on film composition and structure. The SHG microscopy results are in good agreement with the efficiency of electrostatic force microscopy writing and allow us to predict the microscopic dielectric memory efficiency, both in contact and contact-less ways. Received: 15 January 2001 / Revised version: 27 March 2002 / Published online: 6 June 2002     

Ferroelectric properties of Pr and Nb co-substituted Sr0.8Bi2.2Ta2O9 thin films

Thin film of both A- and B-site co-substituted Sr_0.8Bi_2.2Ta₂O₉ (SBT) by Pr³⁺ and Nb⁵⁺, i.e. Sr_0.8Pr_0.1Bi_2.1Ta_1.5Nb_0.5O₉ (SPBTN) was fabricated on Pt/Ti/SiO₂/Si substrates by metalorganic decomposition method. The Nb⁵⁺ substitution at B-site and Pr³⁺ substitution at A-site enhanced the remanent polarization and reduced the coercive field of the films, respectively. The remanent polarization (2P_r) value of the SPBTN film was 22 μC/cm². The coercive field (2E_c) value of the SPBTN film was 102 kV/cm, which was much lower than that of SBTN (165 kV/cm). The effects of substitution on structural and ferroelectric properties of SBT were discussed in detail. As a result, the A- and B-sites co-substitution may be one of the promising ways to improve ferroelectric properties of SBT.     

Influence of 90° domain switching on the physical properties of tetragonal barium titanate single crystals

In this paper, we report the influence of 90° domain switching on the physical properties of tetragonal BaTiO₃ single crystals. It is found that the contribution of 90° domain switching to the piezoelectric response is much larger in magnitude than the contribution of the direct piezoelectric effect under large external mechanical stress. Simultaneously, the interconversion of a and c crystallographic axes and the large actuation strain as high as 1% is induced by 90° domain switching in the tetragonal BaTiO₃ single crystal.     

Manipulation and soldering of carbon nanotubes using atomic force microscope

Manipulation of carbon nanotubes (CNTs) by an atomic force microscope (AFM) and soldering of CNTs using Fe oxide nanoparticles are described. We succeeded to separate a CNT bundle into two CNTs or CNT bundles, to move the separated CNT to a desirable position, and to bind it to another bundle. For the accurate manipulation, load of the AFM cantilever and frequency of the scan were carefully selected. We soldered two CNTs using an Fe oxide nanoparticle prepared from a ferritin molecule. The adhesion forces between the soldered CNTs were examined by an AFM and it was found that the CNTs were bound, though the binding force was not strong.     

Piezoelectric and ferroelectric properties of [(K0.4725Na0.4725)Li0.055]NbO3–(Ag0.5Li0.5)TaO3 lead‐free ceramics

New lead‐free piezoelectric (1 – x)[(K_0.4725Na_0.4725)Li_0.055]NbO₃– x (Ag_0.5Li_0.5)TaO₃ [(1 – x)KNNL–x ALT] ceramics were prepared by conventional sintering. Piezoelectric and ferroelectric properties and Curie temperature of the ceramics were studied. The (1 – x)KNNL–x ALT (x = 0.04) ceramics exhibit good properties (d₃₃ ～ 252 pC/N, k_p ～ 41%, T_C ～ 471 °C, T_o–t = 47 °C, P_r = 33.1 μC/cm², E_c = 10.6 kV/cm). These results show that (1 – x)KNNL–x ALT (x = 0.04) ceramic is a promising lead‐free piezoelectric material for high temperature application. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Bias-induced spatially resolved growth and removal of Si-oxide by atomic force microscopy

Three mechanisms for spatially resolved growth and removal of oxide on silicon substrates have been investigated. Thermally grown oxide layers with thicknesses in the range 2–6 nm were the distinctive feature of the system. The layers were characterized and manipulated by methodologies based on atomic force microscopy (AFM) with conducting probes in a vacuum environment of 10^-2–10^-3 Pa. The probe is then effectively a travelling electrode that generates an electrostatic field between the tip and the substrate. Oxide growth was induced for a positive sample bias greater than 5 V, but below the level corresponding to dielectric breakdown. Application of a short pulse of amplitude marginally above that corresponding to dielectric breakdown, on the other hand, had the effect of producing pits of inner diameter of about 10 nm in the pre-existing oxide layer at the point of tip-to-oxide contact. Application of a low positive sample bias (less than that required for measurable oxide growth) in combination with high linear scan speed had the effect of removing a pre-existing oxide layer from the scanned field of view. The most plausible mechanisms are based on transverse ionic diffusion (for oxide growth), controlled dielectric breakdown (for formation of pits) and lateral transport of silicaceous species (for oxide removal). Received: 24 October 2001 / Accepted: 6 January 2002 / Published online: 3 June 2002 RID="*" ID="*"Corresponding author. Fax: +617-3875-7656, E-mail: s.myhra@sct.gu.edu.au     

Strain and Size Effects on Ferroelectric Properties of BaTiO3 Nanofilms

The strain and size effects on the ferroelectric properties of BaTiO3 films are studied using the molecular dynamics method based on a shell model. It is found that from microscopic view, these two effects share the same physical nature, i.e., the resulting crystal cell distortions lead to the separation of negative and positive charge eentres. The strain and size effects are therefore coupled, and the critical thicknesses of films would depend on the in-plane strains, which provides a possible interpretation on the discrepancies among the experimental measurements of the critical thicknesses. A polarization map is given to clearly reflect the relations among the size, strain and polarization of the nano films.     

Characterization of lead free (K0.5Na0.5)NbO3-LiSbO3 piezoceramic

(K_0.5Na_0.5)NbO₃ (KNN) based lead free ceramics have been fabricated by a solid state reaction. In this work, LiSbO₃ (LS) modified KNN based ceramics were sintered at atmospheric pressure and high density (>96% theoretical) was obtained. The detailed elastic, dielectric, piezoelectric and electromechanical properties were characterized by using the resonance technique combined with the ultrasonic method. The full set of material constants for the obtained polycrystalline ceramics were determined and compared to the pure hot pressed KNN counterpart. KNN-LS polycrystalline ceramic was found to have higher elastic compliance, dielectric permittivity and piezoelectric strain coefficients, but lower mechanical quality factor, when compared to pure KNN, exhibiting a “softening” behavior. However, a high coercive field (∼17 kV/cm) was found for the LS modified KNN material. The properties as a function of temperature were determined in the range of −50-250 ^°C, showing a polymorphic phase transition near room temperature, giving rise to improved piezoelectric behavior.     

Physical bounds of metallic nanofingers obtained by mechano-chemical atomic force microscope nanolithography

To obtain metallic nanofingers applicable in surface acoustic wave (SAW) sensors, a mechano-chemical atomic force microscope (AFM) nanolithography on a metallic thin film (50 nm in thickness)/piezoelectric substrate covered by a spin-coated polymeric mask layer (50-60 nm in thickness) was implemented. The effective shape of cross-section of the before and after etching grooves have been determined by using the AFM tip deconvolution surface analysis, structure factor, and power spectral density analyses. The wet-etching process improved the shape and aspect ratio (height/width) of the grooves and also smoothed the surface within them. We have shown that the relaxed surface tension of the polymeric mask layer resulted in a down limitation in width and length of the lithographed nanofingers. The surface tension of the mask layer can be changed by altering the initial concentration of the polymer in the deposition process. As the surface tension reduced, the down limitation decreased. In fact, an extrapolation of the analyzed statistical data has indicated that by decreasing the surface tension from 39 to 10 nN/nm, the minimum obtainable width and length of the metallic nanofingers was changed from about 55 nm and 2 μm to 15 nm and 0.44 μm, respectively. Using the extrapolation’s results, we have shown that the future SAW sensors buildable by this nanolithography method possess a practical bound in their synchronous frequency (∼58 GHz), mass sensitivity (∼6125 MHz-mm²/ng), and the limit of mass resolution (∼4.88 × 10⁻¹⁰ ng/mm²).     

Insulator–semiconductor–metallic state transition induced by electric fields in Mn‐doped NaNbO3

The electro‐forming procedure was applied to NaNbO₃:Mn and NaNbO₃ insulator crystals. The electric current flow induced a transition to the metallic‐type temperature dependence of the resistance. The Mn dopant shortened the time needed for the transition. The LC‐AFM measurement showed a non‐homogeneous distribution in local resistance resulting from the electric field via the AFM tip. We ascribe this effect to percolation in the network of the highly conducting filaments, whose formation is facilitated by the Mn ions. We conclude that the insulator–metal transition is induced within a subsystem of extended defects already existing in the NaNbO₃:Mn crystal lattice host. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Dielectric and Piezoelectric Properties of Sodium Bismuth Titanate Ceramics with KCe Substitution

The piezoelectric properties of the (KCe)-substituted sodium bismuth titanate (Na_0.5Bi_4.5Ti₄O₁₅, NBT) piezoelectric ceramics are investigated. The piezoelectric properties of NBT ceramics are significantly enhanced by (KCe) substitution. The Curie temperature Tc, and piezoelectric coefficient d₃₃ for the (KCe)-substituted NBT are found to be 663ºC, and 27pC/N, respectively. Dielectric and annealing spectroscopy resent that the (KCe) co-substituted NBT piezoelectric ceramics possess stable piezoelectric properties.     

Screen charge transfer by grounded tip on ferroelectric surfaces

We have investigated polarization reversal and charge transfer effects by a grounded tip on 50 nm thick ferroelectric thin films using piezoelectric force microscopy and Kelvin force microscopy. We observed the polarization reversal in the center of written domains, and also identified another mechanism, which is the transfer of screen charges toward the grounded tip. In order to overcome these phenomena, we successfully applied a modified read/write scheme featuring a bias voltage. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Simulation of hysteresis loops for polycrystalline ferroelectrics by an extensive Landau-type model

Landau-type phenomenological theory is extended to the polycrystalline ferroelectrics by defining a volume fraction of polarization to simulate polarization hysteresis loops. Using this simple model, polarization hysteresis loops of a model Pb(Zr_0.52Ti_0.48)O₃ ceramic at different fields or temperatures are simulated, it is found that our results are in very good agreement with the experimental data for the saturated as well as the unsaturated loops. Moreover, this model can accurately predict the coercive fields and remnant polarizations under arbitrary applied fields.