Kenny Lau

Colossal Dielectric Behavior of Ga+Nb Co-Doped Rutile TiO2

Stimulated by the excellent colossal permittivity (CP) behavior achieved in In+Nb co-doped rutile TiO2, in this work we investigate the CP behavior of Ga and Nb co-doped rutile TiO2, i.e., (Ga(0.5)Nb(0.5))(x)Ti(1-x)O2, where Ga(3+) is from the same group as In(3+) but with a much smaller ionic radius. Colossal permittivity of up to 10(4)-10(5) with an acceptably low dielectric loss (tan δ = 0.05-0.1) over broad frequency/temperature ranges is obtained at x = 0.5% after systematic synthesis optimizations. Systematic structural, defect, and dielectric characterizations suggest that multiple polarization mechanisms exist in this system: defect dipoles at low temperature (∼10-40 K), polaronlike electron hopping/transport at higher temperatures, and a surface barrier layer capacitor effect. Together these mechanisms contribute to the overall dielectric properties, especially apparent observed CP. We believe that this work provides comprehensive guidance for the design of new CP materials.

Effect of annealing temperature on the morphology and piezoresponse characterisation of poly(vinylidene fluoride-trifluoroethylene) films via Scanning Probe Microscopy

Poly(vinylidene fluoride-trifluoroethylene) (PVDF-TrFE (70/30)) films were synthesized on a gold/glass substrate via spin coating. The films were annealed at a temperature between and . Nanoscale characterisation of the morphology, polarization switching, and local piezoresponse hysteresis loops of PVDF-TrFE film was studied using a scanning probe microscope (SPM). Ferroelectric switchable domains were identified by piezoresponse force microscopy (PFM) for all films. Small grains, with weak piezoresponse character, were observed for films annealed just above the Curie temperature. Acicular grains were obtained when the annealing temperature approached the melting point and the piezoresponse increased. Annealing above the melting point decreased the piezoresponse and the morphology changed dramatically into plate-like structures.

Dipolar-glass-like relaxor ferroelectric behaviour in the 0.5BaTiO3-0.5Bi(Mg1/2Ti1/2)O3 electroceramic

The authors J.W., Y.L., and R.L.W. acknowledge the support of the Australian Research Council (ARC) in the form of Discovery projects. Y.L. also appreciates support from the ARC Future Fellowships program.

Dynamic hysteresis and scaling behaviours of lead-free 0.94Bi0.5Na0.5TiO3–0.06BaTiO3 bulk ceramics

Bismuth sodium titanate–barium titanate (1 − x)Bi0.5Na0.5TiO3–xBaTiO3 (BNT–xBT) ceramics have drawn extensive attention of late as lead-free alternatives to lead zirconate titanate PbZr1−xTixO3 (PZT). In this work, the ferroelectric hysteresis loops of a morphotropic phase boundary (MPB) composition of BNT–6BT were measured under electric fields in the frequency range of 0.01 to 10 Hz and fields ranging from 10 to 70 kV cm−1. The relaxor ferroelectric BNT–6BT exhibits a three-stage evolution of scaling behaviours between the logarithm of hysteresis area 〈A〉 and the logarithm of the amplitude of field E0 at medium–high frequencies (herein 0.1 Hz ≤ f ≤ 10 Hz) and two-stage linear scaling behaviours at low frequency (herein f = 0.01 Hz) in the electric field amplitude E0 term (10 kV cm−1 ≤ E0 ≤ 70 kV cm−1). The emergence of three-stage and two-stage dynamic hysteresis scaling behaviours in the relaxor ferroelectric BNT–6BT are attributed to the complex couple contributions of 180° and non-180° domain walls. The three-stage and two-stage scaling behaviours are integrated considering the time-dependent domain wall switching processes.

Susceptible Ferroelectric/Antiferroelectric Phase Transition near the Surface of Nb-Doped Lead Zirconate Stannate Titanate from Surface Processing.

This work systematically investigated the structure and property of the near-surface and bulk regions of Pb0.99(Nb0.02Zr0.73Sn0.21Ti0.04)O3 ceramics using a combination of X-ray and neutron diffraction, piezoresponse force microscopy, and conventional ferroelectric/piezoelectric characterization. It is found that mechanical force can induce an antiferroelectric/ferroelectric phase transition within micrometers of the surface. Such a phase transition is strongly dependent on the processing scenario, leading to differences from the bulk region. This work provides crucial insights into the sensitivity of this class of AFE materials. Clearly, surface processing conditions must be taken into account for both accurate structural determination and practical applications.

Negative magnetodielectric effect in CaCu3Ti4O12

This work was supported by the National Natural Science Foundation of China (Grant No. 11004106) and the National 973 Project (Nos. 2011CB922101 and 2009CB623303).

Patterned photochemical deposition on domain engineered ferroelectric single crystals

The photochemical deposition of silver on (001)-oriented 0.25Pb(In<inf>1/2</inf>Nb<inf>1/2</inf>)O<inf>3</inf>-0.44Pb(Mg<inf>1/3</inf>Nb<inf>2/3</inf>)O<inf>3</inf>-0.31PbTiO<inf>3</inf> (PIN-PMN-PT) ferroelectric single crystals is investigated via piezoresponse force microscopy (PFM) and Kelvin probe force microscopy (KPFM). Selective photochemical deposition within c⁺ domains is attained by manipulating the photoreaction time. Enhanced photochemical reduction at c⁻/c⁺ domain boundaries is achieved by controlling the domain poling voltage and the scanning direction of the tip during domain switching. These phenomena are explained by polarisation band bending at domain boundaries and tip induced charge injection during domain switching. This work provides insight into obtaining an arbitrary spatial distribution of photodeposited metal on ferroelectric materials.