Zhang Duan-Ming

PROCESSING AND FERROELECTRIC PROPERTIES OF Ti-DOPED BiFeO3 CERAMICS

ABSTRACT To improve the ferroelectric properties in BiFeO3, the effects of ion doping have been investigated. Currently, rare earth element substituted bismuth ferrites have attracted much attention for potential memory material. However, BFO materials are known to suffer from low resistivity and high leakage current. Particular dopants change the ferroelectric and electrical properties depending on the ionic charge and radius. In this work, Bi1.05Ti0.1Fe0.9O3 ceramics were prepared by conventional solid state reaction. The sintering temperatures have been varied from 800 to 860°C in order to investigate the phase determination. Scanning electron microscopy (SEM) study was carried out to find out grain size and morphology. The density and electric properties were evaluated. By introducing a small of Ti ions, large enhancement in both remnant and saturation polarizations of the doped-BiFeO3 was observed.

Characteristics of Plasma Shock Waves Generated in the Pulsed Laser Ablation Process

We modify the Sedov theory to describe plasma shock waves generated in a pulsed laser ablating process. We also study the propagation characteristics of plasma shock waves during the preparation process of functional thin films deposited by a pulsed laser. In particular, we discuss in detail the temporal behaviour of energy causing the difference of the propagation characteristics between the plasma shock wave and the ideal shock wave in the point explosion model. Under the same experimental conditions, the theoretical results calculated with our modified Sedov theory are in good agreement with the existing experimental data.

Vaporization and Plasma Shielding during High Power Nanosecond Laser Ablation of Silicon and Nickel

A thermal model to describe the high-power nanosecond pulsed laser ablation is presented. It involves the vaporization and the following plasma shielding effect on the whole ablation process. As an example of Si target, we obtain the time evolution of the calculated surface temperature, ablation rate and ablation depth. It can be seen that plasma shielding plays a more important role in the ablation process with time. At the same time, the ablation depth with laser fluence based on different models is shown. Moreover, we simulate the pulsed laser irradiation Ni target. The evolution of the transmitted intensity and the variation of ablation depth per pulse with laser fluence are performed. Under the same experimental conditions, the numerical results calculated with our thermal model are more in agreement with the experimental data.

SYNTHESIS AND FERROELECTRIC PROPERTIES OF BiFeO3 THIN FILMS GROWN BY SPUTTERING

ABSTRACT There is currently significant interest in the field of ferroelectric thin film materials and devices, with a strong focus on the integration of thin films on Si-complementary metaloxide semiconductor (CMOS) for nonvolatile memory (Fe-RAM) applications. With dramatically high remnant polarization value, bismuth ferrite (BiFeO3) has emerged as one of the most attractive candidates for the storage capacitor layer. In this paper, BiFeO3 (BFO) thin films have been prepared on a stabilized Pt/Ti/SiO2/Si bottom electrode by RF sputtering. X-ray diffraction (XRD) of the target showed that a single perovskite phase and random polycrystalline structure without impurity or second phase accompanied. The remnant polarization values were measured as functions of working pressure, substrate temperature and the ratio of oxygen to argon, respectively. Optimal conditions for the deposition of BFO films were reported. The best ferroelectrics values have been measured for the sample BFO film.

Effect of Bi2O3 seed layer on crystalline orientation and ferroelectric properties of Bi3.25La0.75Ti3O12 thin films prepared by rf-magnetron sputtering method

Bi3.25La0.75Ti3O12 (BLT) thin films with Bi2O3 seed layers were prepared on Pt(111)/Ti/SiO2/Si substrate by rf-magnetron sputtering method. The effect of annealing procedure, thickness, and position of Bi2O3 seed layer on the structural and electrical properties of BLT thin film was investigated. When using a two-step annealing procedure, the x-ray diffraction pattern indicated that BLT thin film with a Bi2O3 seed layer showed c-axis preference orientation. Compared with Pt/BLT/Bi2O3/Pt structure film, the Pt/Bi2O3/BLT/Bi2O3/Pt structure film showed higher oriented to c direction. The ferroelectric property of BLT thin film improved remarkably with the incorporation of Bi2O3 seed layer. Under the applied voltage of 14 V, the remnant polarization and coercive voltage of the Bi2O3/BLT/Bi2O3 capacitor with 18-nm-thick Bi2O3 seed layer were 45.2 μC/cm2 and 9.2 V, respectively. Moreover, the Pt/Bi2O3/BLT/Bi2O3/Pt film with 18-nm-thick Bi2O3 seed layers exhibited good fatigue endurance even after 6×109 switchin...

The influence of ferroelectric KTN particles on electric properties of 0–3 ferroelectric composites

A triphasic ferroelectric composite is obtained when ferroelectric potassium tantalate niobate particles [KTN] with a high dielectric constant and electric conductivity are embedded in a traditional 0–3 manganese and niobate modified lead zirconate titanate [PMNZT]/polyvinylidene fluoride trifluoroethylene [P(VDF-TrFE)] copolymer biphasic-ferroelectric composite. The electric properties are studied for the ferroelectric composite in which the volume fraction of KTN particles is in the range 0%–24% and KTN is a passive phase. The experimental data show that the volume fraction of KTN particles strongly influence the electric properties of ferroelectric composite, and that the triphasic composite doped with KTN has higher ferroelectric, piezoelectric and pyroelectric properties than the biphasic composite with the same PMNZT volume fraction.

Effects of Depolarization Field and Interfacial Coupling on the Polarization of Ferroelectric Bilayers

A ferroelectric bilayer model considering depolarization field and interfacial coupling is proposed and the expression of the depolarization field is derived. The spatial profiles of spontaneous polarization and hysteresis loops are calculated using the numerical method with and without considering the depolarization field. The effects of the depolarization field and interfacial coupling on the polarization of second-order ferroelectric bilayers are studied systematically. When interfacial coupling is ferroelectric coupling, the interface spontaneous polarization increases and the area of hysteresis loop becomes larger with increasing coupling. When interfacial coupling is antiferroelectric coupling, the depolarization field makes the central loop become smaller and the shape of the hysteresis loop becomes steep. Meanwhile, as interfacial coupling increases, the outer loops stretch further out horizontally and the size of the central loop widens.

Criticality in Two-Variable Earthquake Model on a Random Graph

A two-variable earthquake model on a quenched random graph is established here. It can be seen as a generalization of the OFC models. We numerically study the critical behavior of the model when the system is nonconservative: the result indicates that the model exhibits self-organized criticality deep within the nonconservative regime. The probability distribution for avalanche size obeys finite size scaling. We compare our model with the model introduced by Stefano Lise and Maya Paczuski [Phys. Rev. Lett. 88 (2002) 228301], it is proved that they are not in the same universality class.

A Fractal Model for the Effective Thermal Conductivity of Granular Flow with Non-uniform Particles*

The equipartition of energy applied in binary mixture of granular flow is extended to granular flow with non-uniform particles. Based on the fractal characteristic of granular flow with non-uniform particles as well as energy equipartition, a fractal velocity distribution function and a fractal model of effective thermal conductivity are derived. Thermal conduction resulted from motions of particles in the granular flow, as well as the effect of fractal dimension on effective thermal conductivity, is discussed.

Multiple Partial Attacks on Complex Networks

We numerically investigate the effect of four kinds of partial attacks of multiple targets on the Barabasi-Albert (BA) scale-free network and the Erdos-Renyi (ER) random network. Comparing with the effect of single target complete knockout we find that partial attacks of multiple targets may produce an effect higher than the complete knockout of a single target on both BA scale-free network and ER random network. We also find that the BA scale-free network seems to be more susceptible to multi-target partial attacks than the ER random network.