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In the last few decades, piezoresponse force microscopy (PFM) has been a valuable tool to analyze ferroelectric materials at nanoscale. Domain switching and phase-hysteresis loops acquired by PFM had been taken as a proof of ferroelectricity; however, these two characteristics have been observed in non-ferroelectric materials, generating uncertainty of the characterizations carried out by PFM. To resolve this problem, strategies have been developed but they are difficult to implement or still fail depending on the measurement conditions. In this work, we provide a simple method to effectively differentiate ferroelectric from non-ferroelectric signals in PFM analyses. It is based on the comparison of the phases of the PFM signals obtained at the first and the second harmonics of the contact resonant frequency of the Vac applied between the tip and the bottom electrode. To illustrate the effectiveness and simplicity of the method, analyses were conducted on a ferroelectric PZT film, a non-ferroelectric glass and SrTiO3 sample, and a KNN ceramic with ferroelectric and non-ferroelectric zones. [ABSTRACT FROM AUTHOR]

A dielectric spectroscopic study and an ac conductivity analysis in the 100 Hz–1MHz frequency and 30–450°C temperature ranges are presented for the piezoceramic compound (K0.44Na0.52Li0.04)0.97 La0.01Nb0.9Ta0.103, synthesized by the traditional ceramic method using NaNbO3 as a precursor obtained by the reactive templated grain growth method technique. La doping of KxNa1-xNbO3 (KNN) produces a shift of the phase transition temperatures (orthorhombic-tetragonal and tetragonal-cubic) toward lower temperatures. The measured relative permittivity maximum and the relative permittivity at room temperature are remarkably high. Conductivity behaves according to Jonscher’s law in the 400 Hz–1500 Hz frequency range at temperatures between 75 and 300°C, with values of n1 ≤ 0.70, lower than those reported in the literature for similar compounds. The activation energy in the case of dc (long range) conductivity, 1.72 eV, points out to double ionized oxygen vacancies. This value is higher than the 1.46 eV of undoped KNN, evincing the influence of Li and La in the conduction processes of KNN. [ABSTRACT FROM AUTHOR]

Using Raman spectroscopy, the study of a polymorphic phase transition in the KNNLiTaLa0.01 compound is presented. An analysis of the behavior with temperature, wavenumber and half width at full maximum of the individual bands, corresponding to the vibration modes of the (Nb/Ta)O6 octahedra of the KNNLiTaLa0.01 compound's structure, is performed. This analysis determined that the polymorphic phase transition of the KNNLiTaLa0.01 compound occurs in the 90 to 105°C temperature interval. Using the Hard Mode Spectroscopy method, the value of the critical exponent of the order parameter was determined to be β ≈ ½, indicative of a second order transition. [ABSTRACT FROM AUTHOR]

Single phase Sr[Bi.sub.5-x][La.sub.x][Ti.sub.4]Fe[O.sub.18] (x=0, 0.2) compounds with five-layered Aurivillius structure are synthesized and characterized. The activation energies are found to be frequency dependent and the frequency dependence of the conductivity at different temperatures is analyzed by using Jonscher's power law and the Almond-West conductivity formalism.

The different aging behavior of the Ba0.7Sr0.3Ti0.97Zr0.03O ceramic that presents diffuse phase transition was investigated at different temperatures. The aging of this system is explained by assuming the existence of two different relaxation regions, one associated with rapidly relaxing polarized macroregions (tau 1) and the other to long time relaxing polarized microorganisms (tau 2).

High-resolution transmission electron microscopy (HRTEM) of La0.03Sr0.255Ba0.7Nb(sub 2-y)Ti(sub y)O(sub 6-y/2) LSBNT reveals a modulated structure. This modulation is the result of compositional fluctuations.

The c 66 E values of PZT53/47 doped with 0.6% Gd2O3 show an anomalous behavior near 132°C as a consequence of a ferroelastic transition. A non-linear fit to the experimental data of the elastic stiffness variation Δ c 66 E shows that it behaves according to the theoretical law describing pseudoproper ferroelastic transitions. Through Raman spectrum analysis, the frequency of soft mode A1(1TO) has a minimum in the 132–136°C temperature interval associated with the coupling to the S 6 component of the deformation. The quantitative evaluation of the order parameter by hard mode spectroscopy ratified the occurrence of a ferroelastic phase transition. The behavior of both piezoelectric coefficients d31 and the electromechanical coupling factor k31 can be taken as evidence of the transition showing local maxima at 138°C as a consequence of the maximum deformation during the oscillations of the A1(1TO) mode. [ABSTRACT FROM AUTHOR]

A study of a new ferroelastic phase transition in Pb(Zr0.53Ti0.47)O3:Gd detected at 144 °C, induced by Gd doping is presented. The existence of such phase transition is barely detectable in the permittivity vs. temperature curve; however, it is made evident through the analyses of the temperature coefficient of the resonant frequency Tkf dependence with temperature in the radial mode resonance spectrum. This coefficient has a sharp discontinuity at around 144 °C. Micro Raman spectra show that the Raman modes associated to Pb/Gd and (Zr/Ti)O6 positioned at 93.6 cm-1 E(1TO) and 144 cm-1 E(1LO) have a minimum in intensity around 140 °C. Besides the modes of the tetragonal structure, there are the modes at 67.3 and 77.8 cm-1 corresponding to a rhombohedral structure, appearing at all temperatures. The Raman intensity vs. temperature plots of the different modes shows a minimum around 140 °C that confirms the ferroelastic transition detected in the resonance spectrum. [ABSTRACT FROM AUTHOR]

Ferroelectric hysteresis and aging effects in multiferroic Pb(Fe0.5Nb0.5)O3 ceramics obtained through different precursors are discussed using the hysteresis loop modeling by equivalent circuit. Maximum polarization Pmax, remanent polarization Pr, and coercive field EC as functions of external electric fields are determined. A comparative analysis of Pmax, Pr, and EC parameters obtained from the full and remanent hysteresis loops is presented and correlated with a previous structural, morphological, and small signal dielectric frequency-temperature response study using the impedance spectroscopy technique. Three contributions to the full hysteresis were identified: first, a dipolar contribution; second, space charge movement; and third, orientation of the switchable ferroelectric domains. The smaller contribution of the switchable ferroelectric domains, in contrast to the high polarizability of the compound, is explained by assuming that the grains have a complex inner polydomain structure with a distribution of submicrometric sizes and random orientations. Differences in the dielectric hysteresis and aging behavior between the PFN samples obtained through different precursors are established according to their morphological features and their domain structure inside the grains. [ABSTRACT FROM AUTHOR]

This study is focused in the conduction processes taking place in 0.6 wt % Gd doped lead zirconate titanate samples PbZr0.53Ti0.47O3:Gd (PZT53/47:Gd) in the vicinity of the morphotropic phase boundary. Doped samples show very large dielectric permittivity with respect to that of undoped ones near the transition temperature. The frequency dependent ac conductivity of PZT53/47:Gd ceramics was studied in the 30–450 °C temperature range. X-ray diffraction analyses indicate the incorporation of Gd atoms to the structure. The changes in the dielectric properties as functions of temperature of the doped samples are taken as additional evidence of the incorporation of Gd into the crystal structure. Gd acts as donor center promoting extrinsic n-type conduction. The ac conductivity behavior obeys Jonscher universal relation in the 100 Hz–1 MHz frequency range for temperatures between 30 and 300 °C. The measured conductivity values for Gd doped PZT53/47 are higher than those of pure PZT53/47. According to the correlated barrier hopping model, the preponderant conduction mechanism in the frequency-temperature response was recognized as small polarons hopping mechanism. [ABSTRACT FROM AUTHOR]