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We compute the intrinsic dielectric and piezoelectric properties of single domain, mechanically free, and surface charge compensated PbTiO3 nanocrystals (n-Pt) with no depolarization fields, undergoing a finite size induced first order tetragonal→cubic ferrodistortive phase transition. By using a Landau–Devonshire type free energy functional, in which Landau coefficients are a function of nanoparticle size, we demonstrate substantial deviations from bulk properties in the range <150 nm. We find a decrease in dielectric susceptibility at the transition temperature with decreasing particle size, which we verify to be in conformity with predictions of lattice dynamics considerations. We also find an anomalous increase in piezocharge coefficients near ∼15 nm , the critical size for n-Pt. [ABSTRACT FROM AUTHOR]

We propose a phenomenological intrinsic finite-size effect model for single domain, mechanically free, and surface charge compensated PbTiO3 (PT) nanocrystals with no depolarization fields, undergoing a first-order tetragonal→cubic ferrodistortive phase transition. We then derive a Landau-Devonshire type free-energy functional, which is commensurate with the solution of the free-energy equation for the polar point group 4mm, wherein the nanoparticle size (ξ) is a variable. By using experimental particle size-dependent spontaneous polarization (Pvector s) data for PbTiO3, we compute the Landau coefficients up to the sixth order in the range <150 nm as a function of ξ. This thermodynamic potential takes into account the size dependence of the Landau coefficients in a consistent manner, and is able to predict the size-induced phase transition as well as the metastable tetragonal phase in the cubic phase field. We then construct a free-energy density surface in ΔG-Pvector s-ξ space, which describes the decrease in tetragonal phase stability with decreasing ξ rigorously. [ABSTRACT FROM AUTHOR]

We investigate the nonlinear dielectric properties of 0.9Pb(Mg1/3,Nb2/3)O3·0.1PbTiO3 (PMN-PT) and Ba[Ti0.85,Sn0.15]O3 (BTS) paraelectrics experimentally and theoretically. We measure the nonlinear dielectric response in the parallel plate capacitor configuration, whereby we obtain the low frequency linear permittivity ([variant_greek_epsilon]33), and the higher order permittivities ([variant_greek_epsilon]3333,[variant_greek_epsilon]333333) at 298 K as [variant_greek_epsilon]33PMN-PT=2.1×10-7 and [variant_greek_epsilon]33BTS=4.1×10-8 F/m, [variant_greek_epsilon]3333PMN-PT=-4.9×10-20 and [variant_greek_epsilon]3333BTS=-7.3×10-21 F3 m/C2, and [variant_greek_epsilon]333333PMN-PT=7.6×10-33 and [variant_greek_epsilon]333333BTS=9.85×10-34 F5 m3/C4. By using a self-consistent thermodynamic theory in conjunction with the experimental data, we compute the E3 dependence of electrostatic free energy ΔG, the field-induced polarization P3, and the thermodynamic tunability ∂2P3/∂E32, and prove that electrostatic free energy has to be expanded at least up to the sixth order in the electric field to define the critical field |E3*| at which maximum tunability is attained. We also show that |E3*| is a function on |[variant_greek_epsilon]3333|/[variant_greek_epsilon]333333 only. Consequently, we find |E3*|PMN-PT=8.0×105 V/m and |E3*|BTS=8.6×105 V/m. We compute the engineering tunabilities as ΓPMN-PT=65% and ΓBTS=55%, and then define a normalized tunability ξ to take into account the |E3*| parameter. Thereof, we determine |ξ|PMT-PT=8.1×10-5%/V m-1 and |ξ|BTS=6.4×10-5%/V m-1. Our results reveal that |E3*|BTS>|E3*|PMN-PT although ΓBTS<ΓPMN-PT, unequivocally showing the need for defining a critical field parameter in evaluating the nonlinear dielectric response and tunability, in particular, and in nonlinear dielectrics in general. The results also indicate that the nonlinear dielectric properties of PMN-PT are an order of magnitude higher than that of BTS, which we discuss in the context of structure-property relations of relaxors. [ABSTRACT FROM AUTHOR]

The fatigue response of monolithic piezoelectric 0.65Pb(Mg1/3Nb2/3)O3–0.35PbTiO3-electrostrictive 0.90Pb(Mg1/3Nb2/3)O3–0.10PbTiO3 bilayer composites was investigated experimentally. The monomorph bilayers were cosintered at 1150 °C, and the polarization hysteresis, relative permittivity, displacement, and cyclic fatigue (107 cycles) were measured as a function of piezoelectric-electrostrictive volume fraction (PEVF) ratio. The highest tip displacement of bilayers was found in the 3:1 PEVF monolith, reaching 40 μm at 5 kV/cm applied field strength. By minimizing the electrostrictive layer thickness, tip displacement substantially increased, while maintaining a lower hysteresis than the purely piezoelectric counterpart. Fatigue measurements indicated a 31% decrease in displacement after 107 cycles in 3:1 monoliths, whereas the 1:3 PEVF only showed a 12% decrease under the same conditions. There is a 30% increase in polarization after 107 cycles for 1:1 PEVF bilayers, which is attributed to self-poling due to a diffuse transition layer in the vicinity of the interface. It was found that partial 90° domain switching occurred prior to poling because of the residual stresses in the composite, imposed by the electrostrictive layer and the spontaneous strain associated with the cubic-tetragonal transition in the ferroelectric layer. The results indicate that the electrostrictive layer, which is electrically in series with the piezoelectric one, enhances the fatigue resistance of the monolithic bilayer composites in addition to the increase in tip displacement. [ABSTRACT FROM AUTHOR]

We have studied the evolution of anisotropic epitaxial strains in (110)-oriented sBa0.60Sr0.40dTiO3 paraelectric (m3m) thin films grown on orthorhombic (mm2) (100)-oriented NdGaO3 by high-resolution x-ray diffractometry. All the six independent components of the three-dimensional strain tensor were measured in films with 25-1200-nm thickness, from which the principal stresses and strains were obtained. Pole figure analysis indicated that the epitaxial relations are [001]m3m‖ [001]mm2 and [110]m3m‖[010]mm2 in the plane of the film, and [110]m3m‖ [100]mm2 along the growth direction. The dislocation system responsible for strain relief along [001] has been determined to be u∣b∣(001)=3/4∣b∣. Strain relief along the [110] direction, on the other hand, has been determined to be due to a coupled mechanism given by ∣b∣(110)=∣b∣ and ∣b∣(110)=√3/4∣b∣. Critical thicknesses, as determined from nonlinear regression using the Matthews-Blakeslee equation, for misfit dislocation formation along [001] and [110] direction were found to be 5 and 7 nm, respectively. The residual strain energy density was calculated as ∼2.9×106 J/m3 at 25 nm, which was found to relax an order of magnitude by 200 nm. At 200 nm, the linear dislocation density along [001] and [110] are ∼6.5×105 and ∼6×105 cm-1, respectively. For films thicker than 600 nm, additional strain relief occurred through surface undulations, indicating that this secondary strain-relief mechanism is a volume effect that sets in upon cooling from the growth temperature. [ABSTRACT FROM AUTHOR]

The spontaneous polarization (Ps) and spontaneous strains (xi) in mechanically unclamped and surface charge compensated PbTiO3 nanocrystals were determined as a function of particle size in the range <150 nm by differential scanning calorimetry and x-ray powder diffraction, respectively. Significant deviations from bulk order parameters (P,xi) have been observed as the particle size decreased below ∼100 nm. The critical size (rc) below which the ferroelectric tetragonal phase transforms to the paraelectric cubic phase was determined as ∼15 nm. The depression in transition temperature with particle size is 14 °C at 28 nm. No change in the order of m3m→4mm ferrodistortive phase transition is observed. A simple analysis showed that ΔHtr/(kBT)∼103 at 25 °C for r=16 nm, indicating that the stabilization of the cubic phase at rc cannot be linked to an instability in dipolar ordering due to thermal agitations. Comparison of the spontaneous volumetric strains with the strain induced by surface stress indicated that the effect of surface stress on ferroelectric phase stability was negligible. Anomalies in electrostrictive properties were determined for r→rc. The observed size dependence of PS is attributed to the reduced extent of long-range dipole–dipole interactions that arise due to the changes in bonding characteristics of ions with decreasing particle size in the perovskite lattice, in conformity with a recent study by Tsunekawa et al. [Phys. Rev. Lett. 85 (16), 4340 (2000)]. [ABSTRACT FROM AUTHOR]

Electromechanical properties of a number of ferroelectric films including PbZr[sub x]Ti[sub 1-x]O[sub 3](PZT), 0.9PbMg[sub 1/3]Nb[sub 2/3]O[sub 3]-0.1PbTiO[sub 3](PMN-PT), and SrBi[sub 2]Ta[sub 2]O[sub 9](SBT) are investigated using laser interferometry combined with conventional dielectric measurements. Effective electrostriction coefficients of the films, Q[sub eff], are determined using a linearized electrostriction equation that couples longitudinal piezoelectric coefficient, d[sub 33], with the polarization and dielectric constant. It is shown that, in PZT films, electrostriction coefficients slightly increase with applied electric field, reflecting the weak contribution of non-180° domains to piezoelectric properties. In contrast, in PMN-PT and SBT films electrostriction coefficients are field independent, indicating the intrinsic nature of the piezoelectric response. The experimental values of Q[sub eff] are significantly smaller than those of corresponding bulk materials due to substrate clamping and possible size effects. Electrostriction coefficients of PZT layers are shown to depend strongly on the composition and preferred orientation of the grains. In particular, Q[sub eff] of (100) textured rhombohedral films (x=0.7) is significantly greater than that of (111) layers. Thus large anisotropy of the electrostrictive coefficients is responsible for recently observed large piezoelectric coefficients of (100) textured PZT films. Effective electrostriction coefficients obtained by laser interferometry allow evaluation of the electromechanical properties of ferroelectric films based solely on the dielectric parameters and thus are very useful in the design and fabrication of microsensors and microactuators. © 2001 American Institute of Physics. [ABSTRACT FROM AUTHOR]

An experiment is conducted to study the fatigue properties of monolithic piezoelectric Pb([Mg.sub.1/3],[Nb.sub.2/3])[O.sub.3]-PbTi[O.sub.3] bilayer composites and study them as functions of piezoelectric-electrostrictive volume fraction (PEVF) ratio. The results thus obtained clearly reveal that the electrostrictive layer highly enhances the fatigue resistance and induce residual stresses in such layers, leading to the partial switching of the domains.

Ba0.63Sr0.37TiO3 (BST) films were first deposited on SiC substrates with LNO bottom electrodes by magnetron sputtering. The BST/LNO/SiC thin films exhibit high dielectric tunability and low dielectric loss while maintaining excellent temperature coefficient of dielectric constant in the temperature range between 250 and 350 K. We also investigated the effect of film thickness on the dielectric properties. BST(430 nm)/LNO/SiC film has higher tunability (68.09% @700 kV/cm), lower loss tangent (tanδ = 0.00987) and quite a bit higher figure of merit (FOM = 68.99) as compared with that of BST(300 nm)/LNO/SiC film. Our results demonstrate that combining ferroelectric BST films with SiC substrates is very promising for the development of tunable devices over a large temperature range. [ABSTRACT FROM AUTHOR]

The effects of isotropic and anisotropic epitaxy on the nonlinear dielectric response in (Ba 0.6 ,Sr 0.4 TiO 3 ) thin films were investigated experimentally. Under isotropic epitaxy, it is shown that the misfit is detrimental to the non-linear response of the films with decreasing film thickness. Nonlinear dielectric properties of films with in-plane compression exhibit more pronounced strain dependence, while the same does not set-in in film under tension down to 200 nm in thickness. In the case of anisotropic epitaxy, tunability exhibits directional dependence in the plane of the film and possesses orthorhombic symmetry in accordance to the Curie principle. The nonlinear dielectric response was found to be greater along the compressed directions. [ABSTRACT FROM AUTHOR]

Mechanical activation was successfully used to synthesize nanostructured phase-pure Pb(Zr0.7Ti0.3)O3 (PZT) powders. Lead–zirconium–titanium (PbZrTi) hydrous oxide precursor, synthesized from chemical co-precipitation, was mechanically activated in a NaCl matrix. The synthesized PZT particles were characterized by using X-ray diffraction, field-emission scanning electron microscopy, transmission electron microscopy, laser-light diffraction, and nitrogen adsorption. Thermogravimetric analysis and differential thermal analysis were used to monitor dehydration and phase transformation of PbZrTi hydrous oxide precursor during mechanical activation. The best mechanical activation conditions corresponded to mechanically activating PbZrTi hydrous oxide precursor in a NaCl matrix with a NaCl/precursor weight ratio of 4:1 for 8 h. These conditions resulted in a dispersible phase-pure PZT powder with a median secondary-particle size of ∼110 nm. The properties of PZT 70/30 from mechanically activated powder, as measured on discs sintered at 1150 °C for 2 h, were found to be in close conformity to those obtained by a conventional mixed oxide solid state reaction route. [ABSTRACT FROM AUTHOR]

Presents a study which examined the relation of the size of a PbTiO... to the nature of ferroelectricity arising from dipolar coupling. Experimental details; Results; Discussion.

Polycrystalline Ba0.6Sr0.4TiO3 (BST) films grown on r-plane sapphire exhibit strong variation of in-plane strain over the thickness range of 25–400 nm. At a critical thickness of ∼200 nm, the films are strain relieved; in thinner films, the strain is tensile, while compressive strain was observed in the 400 nm film. Microwave properties of the films were measured from 1 to 20 GHz by the interdigital capacitor method. A capacitance tunability of 64% was observed in the 200 nm film, while thinner films showed improved Q factor. These results demonstrate the possibility of incorporating frequency agile BST-based devices into the silicon on sapphire process. [ABSTRACT FROM AUTHOR]

Strain relaxation in (Ba0.60Sr0.40)TiO3 (BST) thin films on ⟨110⟩ orthorhombic NdGaO3 substrates is investigated by x-ray diffractometry. Pole figure analysis indicates a [010]BST∥[110]NGO and [001]BST∥[001]NGO in-plane and [100]BST∥[100]NGO out-of-plane epitaxial relationship. The residual strains are relaxed at h∼200 nm, and for h>600 nm, films are essentially strain free. Two independent dislocations mechanisms operate to relieve the anisotropic misfit strains along the principal directions. The critical thickness for misfit dislocation formation along [001] and [010] are 11 and 15 nm, respectively. Stress analysis indicates deviation from linear elasticity for h<200. The films with 10

The in-plane dielectric response of [110] oriented Ba0.60Sr0.40TiO3 epitaxial films grown on [100] NdGaO3 is used to determine the field induced polarization at 10 GHz. The nonlinear polarization curve is used to determine the linear and nonlinear permittivity terms for the in-plane principal directions, [001] and [110]. Studied films are in the thickness range of 75–1200 nm, and clearly show the influences that drive tunability down with increasing residual strain. The variation of the tunability, along the [001] direction, proves to be less sensitive to residual strain then the [110] direction, although [110] is capable of greater tunability at low residual strains. [ABSTRACT FROM AUTHOR]