After calculations of various domain-switching current transients under the pulse from electrical circuit parameters, the field dependence of domain-switching speeds is accurately estimated over five orders of magnitude in a wide temperature range of 5.4–280 K from the height of domain-switching current in Pb(Zr0.4Ti0.6)O3 thin films. These estimations are extended following Merz's equation [W. J. Merz, Phys. Rev. 1954, 95, 690] and an ultimate domain-switching current density of 1.4 × 108 A cm−1 is extracted at the highest field of 0.20 MV cm−1. From classical domain-nucleation models with thermal fluctuations, an ultimate (asymptotic high-field) nucleation time of 0.47 ps is derived when the domain sideways motion is kink-nucleation-rate limited.

Sub-Picosecond Processes of Ferroelectric Domain Switching from Field and Temperature Experiments

The phase purity and crystal structure of Pb(1-x)LaxTi(1-x)AlxO3 (0 ≤ x ≤ 0.25) samples (synthesized via the sol-gel process) were confirmed using synchrotron x-ray powder diffraction (XRD) (wavelength, λ =  0.44573 A). Rietveld analyses of powder x-ray diffraction data confirmed the tetragonal structure for compositions with x ≤ 0.18 and cubic structure for the sample with x = 0.25. Temperature-dependent XRD was performed to investigate the structural change from tetragonal to cubic structure phase transition. Raman spectroscopy at room temperature also confirmed this phase transition with compositions. Field emission scanning electron microscopy (FESEM) provided information about the surface morphology while an energy dispersive x-ray spectrometer attached with FESEM confirmed the chemical compositions of samples. Temperature and frequency dependent dielectric studies showed that the tetragonal to cubic phase transition decreased from 680 K to 175 K with an increase in the x from 0.03 to 0.25, respectiv...

Investigation of La and Al substitution on the spontaneous polarization and lattice dynamics of the Pb(1-x)LaxTi(1-x)AlxO3 ceramics

Lead titanate (PbTiO3) is a classical example of a ferroelectric perovskite oxide illustrating a displacive phase transition accompanied by a softening of a symmetry-breaking mode. The underlying assumption justifying the soft-mode theory is that the crystal is macroscopically sufficiently uniform so that a meaningful free energy function can be formed. In contrast to PbTiO3, experimental studies show that the phase transition behaviour of lead-zirconate-titanate solid solution (PZT) is far more subtle. Most of the studies on the PZT system have been dedicated to ceramic or powder samples, in which case an unambiguous soft-mode study is not possible, as modes with different symmetries appear together. Our Raman scattering study on titanium-rich PZT single crystal shows that the phase transitions in PZT cannot be described by a simple soft-mode theory. In strong contrast to PbTiO3, splitting of transverse E-symmetry modes reveals that there are different locally-ordered regions. The role of crystal defects, random distribution of Ti and Zr at the B-cation site and Pb ions shifted away from their ideal positions, dictates the phase transition mechanism. A statistical model explaining the observed peak splitting and phase transformation to a complex state with spatially varying local order in the vicinity of the morphotropic phase boundary is given.

A statistical model approximation for perovskite solid-solutions: a Raman study of lead-zirconate-titanate single crystal

Raman spectra of ferroelectric Pb1−xLaxTiO3, in the tetragonal phase of the material and for different La concentrations, were studied for different temperatures and pressures. While temperature was varied from 8 K to transition temperature (Tc) at atmospheric pressure, applied hydrostatic pressure was increased from zero to transition pressure (Pc) at room temperature. Isobaric and isothermal mode-Gruneisen parameters were calculated from the measured Raman spectra, and previously reported coefficients of thermal expansion [Chen et al., J. Am. Ceram. Soc. 88, 1356 (2005)] and bulk moduli. Also the coefficient of intrinsic anharmonicity was calculated. Although the absolute value of Gruneisen parameters strongly depends on the Raman mode under study, all of them grow as La concentration increases.

High-temperature, high-pressure Raman spectra and their intrinsic anharmonic effects in the perovskite Pb1−xLaxTiO3

The time dependence of the domain switching current density, Jsw(t), under pulsed voltages on a ferroelectric parallel-plate capacitor is the consequence of region-by-region polarization reversals across the film. As the distributive coercive voltage of domain nucleation increases from zero to the maximum applied voltage during the capacitor charging time, Jsw(t) is proportional to the domain switching speed at each time. By transforming the spatially inhomogeneous domain nucleation distribution into a temporal distribution of coercive fields (Ec), a local lnJsw versus Ec−1 plot is derived for each domain, following the Merz equation. This provides insight into the independent domain switching dynamics at different nucleation sites in Pb(Zr0.35Ti0.65)O3 thick films over a large current range. Although the activation field of the slope of the lnJsw(t) versus Ec−1 plot varies with film area and temperature, all the plots extrapolate to a single point (J0, E0) from which the ultimate domain switching current density of J0 =1.4 × 108 A cm−2 at the highest field of E0 = 0.20-0.25 MV cm−1 is derived. Unexpectedly, J0 and E0 are independent of the film thickness and area, after correction for a small interfacial-layer effect. This analysis provides rigorous evidence for nucleation rate-limited domain switching with a subpicosecond nucleation time and the relative unimportance of domain forward-growth time across film thicknesses between 0.14 and 2 μm. This work paves the way to improve the efficiency of ferroelectric thick-film functionality in electronic and optoelectronic devices with ultrafast clock rates.

Subpicosecond Domain Switching in Discrete Regions of Pb(Zr0.35Ti0.65)O3 Thick Films

A detailed Raman scattering study was performed on lanthanum-modified lead titanate (PLT) with compositions varying from pure PbTiO3 to La 20.0 at. %, for temperatures ranging from 8 K to temperatures above the Curie temperature and hydrostatic pressures up to 7.5 GPa. A complete La concentration-pressure-temperature three dimensional phase diagram was determined, by using the E(TO1) soft mode frequency as the main probe.

Pressure-temperature-La concentration three-dimensional phase diagram of La-modified PbTiO3 determined by Raman scattering

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Pressure-temperature-La concentration three-dimensional phase diagram of La-modified PbTiO3 determined by Raman scattering