Polarization switching in radiation damaged ferroelectric crystals

The polarization switching processes in radiation damaged ferroelectrics were studied by the Merz method. In irradiated triglycine sulphate and sodium nitrite, the switching time depends exponentially on the applied electric field. Irradiation increases the importance of nucleation and sideways motion of the domain walls in polarization switching.

Polarization reversal studies in ferroelectric taap

Telluric Acid Ammonium Phosphate (Te(OH)62(NH4)H2PO4(NH4)2HPO4) reffered to as TAAP is a recently discovered class m ferroelectric.1 It undergoes FE-PE transition at 48°C. Switching studies in this crystal has been carried out in the temperature range -14°C to 39°C by applying fields up to 4 kV/cm. Measurements were carried out on (101) plates cut from the crystals grown from solution. X-ray irradiation was carried out at room temperature by means of an x-ray tube operating at 25 kV and 15 mA with copper target. Air drying silver paste was used as electrodes. Samples were checked for hysteresis loop using a modified Sawyer-Tower circuit. The Ps value obtained from the loop is 2.1 μC/cm2 which is comparable to the earlier reported value. It was however noticed that the loop was slightly shifted to right with respect to the origin indicating the presence of a small internal bias which was 100 V/cm in the virgin crystal. This bias could not be removed even after repeated crystallization. On irradiation the internal biasing field increased which was indicated by a further shift of the hysteresis loop. The bias seems to saturate at about 750 V/cm for which the crystal had to be irradiated for about 3 hours.

Polarization switching studies in ferroelectric glycine phosphite single crystals

Glycine Phosphite [NH3CH2COOH3PO3], abbreviated as GPI, undergoes a para-ferroelectric phase transition from the monoclinic symmetry P2(1)/a to P2(1) at 224.7 K. We report here a systematic study of the polarization switching process in this crystal. Growth of these crystals from aqueous solution has been undertaken employing both solvent evaporation and slow cooling methods. Hysteresis loop measurements along the polar b-axis yielded a spontaneous polarization value of 0.5 muC/cm(2) and a coercive field of 2.5 kV/cm. Conventional Merz technique was employed for polarization switching studies, wherein bipolar square pulses were applied to the sample to induce domain reversal. The transient switching pulse that flows through the sample on application of the field was recorded. The maximum switching time required for domain switching was measured both as a function of electric field and temperature. The experimentally observed switching curves were fitted with the model based on the Pulvari-Kuebler theory of nucleation and growth of domains. From the experimental data, the values of mobility and activation field were obtained. It was observed that switching process in this crystal is predominantly governed by the forward growth of domain walls in the high field region. However, switching process in GPI crystal was found to be slower than that found in other glycine based ferroelectric crystals.

Ferroelectric interaction and polarization studies in BaTiO3/SrTiO3 superlattice

Ferroelectric superlattice structures consisting of alternating layers of BaTiO3 and SrTiO3 with variable interlayer thickness were grown on Pt (111)/TiO2/SiO2/Si (100) substrates by pulsed laser deposition. The presence of superlattice reflections in the x-ray diffraction pattern clearly showed the superlattice behavior of the fabricated structures over a range of 6.4–20 nm individual layer thicknesses. Depth profile conducted by secondary ion mass spectrometry analysis showed a periodic concentration of Ba and Sr throughout the film. Polarization hysteresis and the capacitance-voltage characteristics of these films show clear size dependent ferroelectric characteristics. The spontaneous (Ps) and remnant (Pr) polarizations increase gradually with decreasing periodicity, reach a maximum at a finite thickness and then decrease. The competition between the size effect and long-range ferroelectric interaction is suggested as a possible reason for this phenomenon. The temperature dependence of Ps and Pr shows a single ferroelectric phase transition, and the Curie temperature is estimated to be about 316 K. The curve shows that the ferroelectric superlattice tends to form an artificial material, responding as a single structure with an averaged behavior of both the parent systems.

Anomalous polarization in the antiferroelectric-ferroelectric phase coexistence state in PbZrO3-Bi(Mg1/2Ti1/2)O-3

The ferroelectric system (1-x)PbZrO3-(x)Bi(Mg1/2Ti1/2)O-3 has been investigated as a function of composition, temperature, and electric field by x-ray powder diffraction, dielectric, and ferroelectric measurements. Within the solubility limit (x similar to 0.25), the system evolves from an orthorhombic-antiferroelectric to rhombohedral-ferroelectric state through a phase coexistence region. The highest polarization was found not for the composition exhibiting a pure ferroelectric state, but for a composition x = 0.15 exhibiting ferroelectric + antiferroelectric phase coexistence close to the rhombohedral phase boundary. Electric poling of the equilibrium two-phase state led to irreversible enhancement in the rhombohedral phase fraction suggesting that the enhanced polarization is related to the enhanced polarizability of the lattice due to first order criticality as in ferroelectric-ferroelectric morphotropic phase boundary systems. (C) 2013 AIP Publishing LLC.

A study of capacitance-voltage characteristics of lead zirconate titanate ferroelectric thin films and their usage to investigate polarization and coercive field.

Capacitance-voltage (C-V) characteristics of lead zirconate titanate (PZT) thin films with a thickness of 130 nm were measured between 300 and 533 K. The transition between ferroelectric and paraelectric phases was revealed to be of second order in our case, with a Curie temperature at around 450 K. A linear relationship was found between the measured capacitance and the inverse square root of the applied voltage. It was shown that such a relationship could be fitted well by a universal expression of C/A = k(V+V(0))(-1/2) and that this expression could be derived by expanding the Landau-Devonshire free energy at an effective equilibrium position of the Ti/Zr ion in a PZT unit cell. By using the derived equations in this work, the free energy parameters for an individual material can be obtained solely from the corresponding C-V data, and the temperature dependences of both remnant polarization and coercive voltage are shown to be in quantitative agreement with the experimental data.

Programmable ZnO nanowire transistors using switchable polarization of ferroelectric liquid crystal

We demonstrate modulations of electrical conductance and hysteresis behavior in ZnO nanowire transistors via electrically polarized switching of ferroelectric liquid crystal (FLC). After coating a nanowire channel in the transistors with FLCs, we observed large increases in channel conductance and hysteresis width, and a strong dependence of hysteresis loops on the polarization states associated with the orientation of electric dipole moments along the direction of the gate electric field. Furthermore, the reversible switching and retention characteristics provide the feasibility of creating a hybrid system with switch and memory functions. © 2013 American Institute of Physics.

Polarization switching induced decrease of bulk resistivity in ferroelectric Pb(Zr0.45Ti0.55)O3 thin films and a method to improve their fatigue endurance

Significant reduction of the bulk resistivity in a ferroelectric Pb(Zr 0.45Ti0.55)O3 thin film is observed before the remnant polarization started to decrease noticeably at the onset of its fatigue switching process. It is associated with the increase of charge carriers within the central bulk region of the film. The decrease of bulk resistivity would result in the increase of Joule heating effect, improving the temperature of the thin film, which is evaluated by the heat conduction analysis. The Joule heating effect in turn accelerates the polarization reduction, i.e. fatigue. Enhancing the heat dissipation of a ferroelectric capacitor is shown to be able to improve the device's fatigue endurance effectively. © 2013 Chinese Physical Society and IOP Publishing Ltd.

First-Order Reversal Curve Probing of Spatially Resolved Polarization Switching Dynamics in Ferroelectric Nanocapacitors

Spatially resolved polarization switching In ferroelectric nanocapacitors was studied on the sub-25 nm scale using the first-order reversal curve (FORC) method. The chosen capacitor geometry allows both high-veracity observation of the domain structure and mapping of polarization switching in a uniform field, synergistically combining microstructural observations and probing of uniform-field polarization responses as relevant to device operation. A classical Kolmogorov-Avrami-Ishibashi model has been adapted to the voltage domain, and the individual switching dynamics of the FORC response curves are well approximated by the adapted model. The comparison with microstructures suggests a strong spatial variability of the switching dynamics inside the nanocapacitors.

Polarization retention loss in PbTiO3 ferroelectric films due to leakage currents

The relationship between retention loss in single crystal PbTiO3 ferroelectric thin films and leakage currents is demonstrated by piezoresponse and conductive atomic force microscopy measurements. It was found that the polarization reversal in the absence of an electric field followed a stretched exponential behavior 1-exp[-(t/k)(d)] with exponent d>1, which is distinct from a dispersive random walk process with d <. The latter has been observed in polycrystalline films for which retention loss was associated with grain boundaries. The leakage current indicates power law scaling at short length scales, which strongly depends on the applied electric field. Additional information of the microstructure, which contributes to an explanation of the presence of leakage currents, is presented with high resolution transmission electron microscopy analysis.

The use of pulsed electric acoustic technique for measuring the polarization reversal in ferroelectric ceramic samples

The pulsed electric acoustic technique, PEA, has been usually applied to probe space charge profiles in polymers. Preliminary PEA results using a ferroelectric ceramic are presented. If the reverse applied electric field i of the order of the coercive field the switching polarization process occurs in a period larger than hundreds of seconds. Such a slow process allows one to use the PEA setup to follow the polarization switching dynamics and determine the electric field profile. The PEA signal obtained in the lead zirconate-titanate doped with niobium ceramic, PZTN, indicates that the polarization distribution and field are not uniform during the switching period. We were also able to observe that the acoustic wave velocity and attenuation depends on the stage of the polarization switching, which agrees with results obtained using the ultrasonic method.