Weak Frequency Dispersion Research Articles

Lead-Free Niobate Ceramics with Relaxor-Like Properties

Ceramics of (1 − x)NaNbO3− (x)Na0.5Bi0.5TiO3 and (1 − x)NaNbO3 − (x)Sr0.5 NbO3 binary solid solutions exhibit strongly diffused permittivity maxima, when x exceeds a threshold value of about 0.15 and 0.1, respectively, but show weak frequency dispersion of permittivity and small frequency shift of the permittivity maximum temperature. Addition of LiNbO3 to these compositions increases the permittivity maximum temperature and greatly enhances the frequency dependence of both the permittivity maximum temperature and permittivity values.

Structure and dielectric behavior of Pb(Mg1/3Nb2/3)O3–Pb(Ni1/3Nb2/3)O3–Pb(Zn1/3Nb2/3)O3–PbTiO3 ferroelectric ceramics near the morphotropic phase boundary

Pb(Mg1/3Nb2/3)O3–Pb(Ni1/3Nb2/3)O3–Pb(Zn1/3Nb2/3)O3–PbTiO3 (PMN–PNN–PZN–PT) ceramics with compositions of (1−x)(0.14PZN–0.56PNN–0.30PT)−x(0.528PMN–0.132PNN–0.340PT) (x=0.2,0.4,0.6,0.8) were prepared using the conventional mixed-oxide technique. X-ray diffraction results demonstrate that all the samples lie within the morphotropic phase boundary (MPB) region in the pure perovskite structure. The temperature dependence of the dielectric constant of the ceramics has been investigated in detail. All samples are characterized by a pronounced diffuse phase transition and weak frequency dispersion, and can no longer be regarded as typical relaxors. Excellent dielectric properties have been obtained for the selected compositions. The εm value of the composition with x=0.8 at 1kHz reaches as high as 36,800, which implies that the quaternary compositions near the MPB merit further study.

The AC Conductivity and Dielectric Constant of (006) Textured LiNbO3 Films

c-axis oriented LiNbO3 films are grown by pulsed laser deposition technique on the Si substrate using a transparent conducting Al doped ZnO inter-layer. Film quality has been examined by means of X-ray diffraction and atomic force microscopy. Dielectric properties of the c-axis oriented LiNbO3 film as a function of frequency (0.1 KHz to 1.0 MHz) and temperature (100 to 450 K) in metal-insulator-metal configuration are investigated. Large frequency dispersion was observed in the dielectric constant at higher temperatures (> 300 K), whereas below room temperature a weak frequency dispersion and small temperature dependence was found. The ac conductivity and dielectric data are in good agreement with the reported results on LiNbO3 single crystals. Communicated by Prof. Amar S. Bhalla

Lead-Free Relaxor Ferroelectric Ceramics in NaNbO3-Sr0.5NbO3-LiNbO3 Solid Solution System

Ceramics of (1-x)NaNbO3-(x)Sr0.5NbO3 solid solutions exhibit strongly diffused permittivity maxima near the room temperature, but show weak frequency dispersion of permittivity and small frequency shift of the permittivity maximum temperature, T m . Addition of LiNbO3 greatly enhances the frequency dependence of both T m and permittivity values.

A numerical study of submarine–landslide–generated waves and run–up

A mathematical model is derived to describe the generation and propagation of water waves by a submarine landslide. The model consists of a depth–integrated continuity equation and momentum equations, in which the ground movement is the forcing function. These equations include full nonlinear, but weak frequency–dispersion, effects. The model is capable of describing wave propagation from relatively deep water to shallow water. Simplified models for waves generated by small seafloor displacement or creeping ground movement are also presented. A numerical algorithm is developed for the general fully nonlinear model. Comparisons are made with a boundary integral equation method model, and a deep–water limit for the depth–integrated model is determined in terms of a characteristic side length of the submarine mass. The importance of nonlinearity and frequency dispersion in the wave–generation region and on the shoreline movement is discussed.

Nonlinear Dispersion of Surface Gravity Waves in Shallow Water*

The nonlinear dispersion of random, directionally spread surface gravity waves in shallow water is examined with Boussinesq theory and field observations. A theoretical dispersion relationship giving a directionally averaged wavenumber magnitude as a function of frequency, the local water depth, and the local wave spectrum and bispectrum is derived for waves propagating over a gently sloping beach with straight and parallel depth contours. The linear, nondispersive shallow water relation is recovered as the first-order solution, with weak frequency and amplitude dispersion appearing as second-order corrections. Wavenumbers were estimated using four arrays of pressure sensors deployed in 2‐6-m depth on a gently sloping sandy beach. When wave energy is low, the observed wavenumbers agree with the linear, finitedepth dispersion relation over a wide frequency range. In high energy conditions, the observed wavenumbers deviate from the linear dispersion relation by as much as 20%‐30% in the frequency range from two to three times the frequency of the primary spectral peak, but agree well with the nonlinear Boussinesq dispersion relation, confirming that the deviations from linear theory are finite amplitude effects. In high energy conditions, the predicted frequency and amplitude dispersion tend to cancel, yielding a nearly nondispersive wave field in which waves of all frequencies travel with approximately the linear shallow water wave speed, consistent with the observations. The nonlinear Boussinesq theory wavenumber predictions (based on the assumption of irrotational wave motion) are accurate even within the surf zone, suggesting that wave breaking on gently sloping beaches has little effect on the dispersion relation.

Ag(Ta, Nb)O 3 thin-film low-loss variable interdigital capacitors

Epitaxial silver tantalate-niobate Ag(Ta, Nb)O3 (ATN) films have been grown on LaAlO3(001) MgO(001), and Al2O3(011_2) single crystals by pulsed ablation of stoichiometric AgTa0.38Nb0.62O3 ceramic target. Rutherford backscattering spectroscopy has revealed Ag0.9Ta0.42Nb0.58O3−δ composition of fabricated films. Micrometer size interdigital capacitor structures have been defined photolithographically on the top surface of ATN films. ATN/LaAlO3 thin-film capacitors exhibit superior overall performance: loss tangent as low as 0.0033 @1 MHz, dielectric permittivity 224 @1 kHz, weak frequency dispersion of 5.8% in 1 kHz to 1 MHz range, tunability as high as 16.8%, factor K=tunability/tan δ higher than 48, and leakage current as low as 230 nA/cm2 @100 kV/cm. ATN films on MgO show the lowest loss factor of 0.0025 @1 MHz and the weakest frequency dispersion of 2.5×10−8 Hz−1.

Ferroelectric silver niobate-tantalate thin films

Submicron thick ferroelectric AgTa0.38Nb0.62O3 (ATN) films have been prepared by pulsed laser deposition technique onto Pt80Ir20 polycrystalline and La0.7Sr0.3CoO3/LaAlO3 single crystal substrates. ATN/Pt80Ir20 films have been found to be (001) preferentially oriented, while the epitaxial quality of ATN/La0.7Sr0.3CoO3/LaAlO3 heterostructures has been ascertained. Comparative analysis of the temperature and frequency dependencies of the dielectric permittivity ε′ and loss tan δ in ATN films and bulk ceramics shows that in films: the coupled structural-ferroelectric monoclinic M1-to-monoclinic M2 phase transition occurs at the temperature 60° lower than in ceramics, thus the temperature stability of ε′ and tan δ in films is improved and occurs in extended temperature range. Reliable tracing of the ferroelectric hysteresis polarization versus electric loops indicates the ferroelectric state in ATN films at temperatures below 125 K and yields the remnant polarization of 0.4 μC/cm2 @77 K. Weak frequency dispersion, high temperature stability of the dielectric properties, as well as low processing temperature of 550 °C, are the most attractive features of ATN films.

Crystalline and Electrical Properties of Ferroelectric Silver Niobate-tantalate thin Films

AbstractFor the first time AgTa0.38Nb0.62O3 (ATN) films have been grown on the La0.7Sr0.3CoO3 (LSCO)/LaAlO3 single crystal as well as onto Pt80Ir20 (PtIr) polycrystalline substrate. Comprehensive X-ray diffraction analyses reveal epitaxial quality of ATN and LSCO films on the LaAlO3(001) substrate, while ATN/PtIr films have been found to be (001) preferentially oriented. Dielectric spectroscopy performed for ATN films and bulk ceramics in a wide temperature range 77 to 420 K shows the structural monoclinic M1-to-monoclinic M2 phase transition occurs in films at the temperature 60 °C lower than in ceramics. The tracing of the ferroelectric hysteresis P-E loops indicates the ferroelectric state in ATN films at temperatures below 125 K and yields remnant polarization of 0.4 μC/cm2 @ 77 K. Weak frequency dispersion, high temperature stability of dielectric properties as well as low processing temperature of 550 °C make ATN films to be attractive for various applications.