Gang Peng

Effect of low Fe3O4 doping in La0.67Ca0.33MnO3

The electrical and magnetic transport behaviour of composite samples of (1−x)La0.67Ca0.33MnO3+xFe3O4 with x = 0, 0.1%, 1% and 2% were studied in a temperature interval 10–300xa0K and for magnetic fields H = 0, 0.3, 0.5, 1 and 3xa0T. The temperature and magnetic field dependence of resistivity of composites show that the low Fe3O4 doping levels have important effects on electrical and magnetic transport behaviour of La0.67Ca0.33MnO3. Especially, compared to pure La0.67Ca0.33MnO3, a new insulator–metal (I–M) transition was observed at a lower temperature TP2 in all Fe3O4 doped La0.67Ca0.33MnO3 composites, which may result from the existence of a new phase related to Fe3O4 dopant at grain boundaries and surfaces of La0.67Ca0.33MnO3 phases. It is of interest to note that the new I–M transition temperature, TP2, is almost independent of the magnetic field. Meanwhile, an obvious magnetoresistance effect was observed between temperatures TP1 and TP2. The results were discussed by considering the results of scanning electron microscopy, x-ray diffraction, dielectric relaxation and susceptibility analysis.

Grain boundaries and low-field transport properties in colossal magnetoresistance materials

The grain-boundary structure and the temperature dependence of resistivity were investigated for (1-x)LCMO + xYSZ, where LCMO and YSZ represent La2/3Ca1/3MnO3 and yttria-stabilized zirconia, respectively. It is shown that the YSZ doped samples for x 2%. The metal-insulator transition temperature (Tp) decreases for x 2% as x is increased. LFMR increases with x for x 2%. The experimental observations are discussed on the basis of scanning electron microscopy (SEM) analysis, which reveals YSZ appearing at the grain boundaries of LCMO for x 2%.

The influence of the thickness of TiO2 seeding layer on structural and electrical properties of Bi3.15Nd0.85Ti3O12 thin films

Thin films of Bi3.15Nd0.85Ti3O12(BNT) and BNT with various TiO2 seeding layer thicknesses BNT-Tx (x = 10, 20, 30 nm) were fabricated on Pt/Ti/SiO2/Si substrates by the sol–gel method. The influence of the TiO2 seeding layer thickness on the structural and the electrical properties of BNT thin films was investigated. The x-ray diffraction pattern indicated that the BNT thin film with a TiO2 seeding layer showed a-axis preference orientation. The Pr value was a maximum for the BNT-T20 film and decreased with both decreasing and increasing thickness. The BNT-T20 film had the largest er and the lowest tanδ. The leakage current density of the BNT thin films with various TiO2 seeding layer thicknesses was generally in the order of 10−6–10−5 A cm−2. The surface micrograph of BNT-Tx films was more homogeneous and dense than that without a seeding layer.

Modeling ferroelectric capacitors based on the dipole switching theory

In this paper, we derived a compact model for the description of the P–E hysteresis behavior based on the dipole switching theory. Simulation results show good agreement with the experiment for various hysteresis loops, and the mathematical description can be easily combined with an electronic design automation software for circuit simulation. Therefore, the model can be used for both circuit simulation and providing better intuition for the ferroelectric material behavior.

Enhancement of magnetoresistances at room temperature in YSZ doping La0.67Sr0.33MnO3 system

Abstract The temperature dependence of the resistance of composite samples (1− x )La 0.67 Sr 0.33 MnO 3 + x YSZ with different YSZ doping level x was investigated at magnetic fields 0–3xa0T, where YSZ represents yttria-stabilized zirconia. Results show that the YSZ dopant does not only adjust the metal–insulator transition temperature, but also increases the magnetoresistance effect. With increase of YSZ doping level for the range of x T P of the composites decrease, but T P increases with increase of x further for the range of x >2%. Meanwhile, in the YSZ-doped composites, a broad metal–insulator transition temperature region was found at zero and low magnetic field, which results in an obvious enhanced magnetoresistance in the temperature range 10–350xa0K. Specially, a larger magnetoresistance value was observed at room temperature at 3xa0T, which is encouraging with regard to the potential application of magnetoresistance materials.

A COMPACT MODEL FOR THE SIMULATION OF FERROELECTRIC CAPACITOR

ABSTRACT A compact model for description of the ferroelectric hysteresis loop behavior based on the dipole switching theory was derived. A cell of ferroelectric crystal is just as an equivalent dipole, so the hysteresis loop characteristic of ferroelecticity is the polarization characteristic of dipole in the electric field. The simulation results show good agreement with the experiment data for various hystersis loops. Therefore the model can be used for both circuit simulation and provide better intuition into the ferroelectric material behavior.

THE EFFECT OF A-SITE La AND Nd SUBSTITUTION ON THE RESIDUAL STRESS OF Bi4Ti3O12 THIN FILMS FABRICATED BY SOL-GEL METHOD

ABSTRACT In this paper, thin films of Bi4Ti3O12 (BTO), Bi3.25La0.75Ti3O12 (BLT) and Bi3.15Nd0.85Ti3O12 (BNT) were fabricated on Pt/Ti/SiO2/Si substrates by sol-gel method. The structures and ferroelectric properties of the polycrystalline films are studied and the correlation between substitution and residual stress are discussed in detail. The results show that, the ferroelectric and fatigue properties of the BLT and BNT films are improved greatly, compared with those of the BTO thin film. The Pr values of BLT and BNT are 13.14 and 21.23 μC/cm2, respectively. X-ray diffraction result shows that the measured residual stress is tensile stress for all films. After A-site substitution, the value of tensile stress for the BTO films has increased and the stress value is maximal for the BNT film. The calculated intrinsic residual stress values are 288.4, 418.4 and 608.2 MPa for BTO, BLT and BNT, respectively.

FERROELECTRIC PROPERTIES OF Zr-DOPED Bi3.15ND0.85Ti3O12 THIN FILM DEPOSITED BY A SOL-GEL METHOD

ABSTRACT Nd3 +-substituted and Zr4 +-substituted bismuth titanate BNT and BNTZx Bi3.15Nd0.85Ti3-xZrx O 12(BNTZx, x = 0, 2%, 4%, 6%, 8%, 10%) thin films were fabricated on Pt/Ti/SiO2/Si substrates by sol-gel method at 750°C. XRD shows that A-site Nd3 + and B-site Zr4 + substitutions do not destroy the layered structure. The remanent polarization (2Pr) values under the voltage of 12v were 20.2, 22.5, 23.7, 26.4, 21.7 and 17.9 μ c/cm2, respectively, for x = 0, 2%, 4%, 6%, 8%, 10%, with the BNTZ6 film has the maximum 2Pr value. While the BNTZx films had an coercive voltage (Vc) value of 3.5v which was similar to that of the BNT film. The fatigue date shows that the BNTZx films have an inferior fatigue characteristics than the BNT film.

Effect of A-site deficiency on electrical transport properties of YSZ doped manganites

Abstract The electrical transport properties of the composite samples: A-site stoichiometry (1−x)La2/3Ca1/3MnO3+xYSZ and A-site deficiency (1−x)(La2/3Ca1/3)0.95MnO3+xYSZ with different YSZ percentage x were investigated, respectively. The similar metal–insulator transition at different temperature TP was observed in the two types of composite samples: With increasing of the YSZ percentage, the zero-field resistivity of the composite samples increases and TP shifts to the low temperature for the range of x 2%. For the same YSZ percentage x, TP of (1−x)La2/3Ca1/3MnO3+xYSZ is lower than that of (1−x)(La2/3Ca1/3)0.95MnO3+xYSZ. The different effects between the two type composites were also observed in the nonlinear current–voltage (I–V) behaviors. The results suggest that A-site deficiency and YSZ dopant can be used to adjust purposely the metal–insulator transition temperature and resistivity of composites.