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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 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 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]

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]

In-plane dielectric properties of <110> oriented epitaxial (Ba0.60Sr0.40)TiO3 thin films in the thickness range from 25-1200 nm have been investigated under the influence of anisotropic epitaxial strains from <100> NdGaO3 substrates. The measured dielectric properties show strong residual strain and in-plane directional dependence. Below 150 nm film thickness, there appears to be a phase transition due to the anisotropic nature of the misfit strain relaxation. In-plane relative permittivity is found to vary from as much as 500-150 along [110] and [001] respectively, in 600 nm thick films, and from 75 to 500 overall. Tunability was found to vary from as much as 54% to 20% in all films and directions, and in a given film the best tunability is observed along the compressed axis in a mixed strain state, 54% along [110] in the 600 nm film for example. [ABSTRACT FROM AUTHOR]