Pingsun Qiu

Thermoelectric properties of Ni-doped CeFe4Sb12 skutterudites

We have prepared Ni-doped p-type skutterudites CeyFe4−xNixSb12 and systematically studied their thermoelectric properties. The lattice parameters of these skutterudites are found to be sensitive to both the Ni content and Ce-filling fraction. With increasing Ni content, the electrical conductivity decreases and the Seebeck coefficient increases, consistent with the expected decrease in hole concentration due to the extra electrons introduced by Ni. All Ni-doped samples possess similar band gap values. We also find that the Ni-doped CeyFe4−xNixSb12 system has electrical transport properties similar to those of Co-doped CeyFe4−xCoxSb12 system at a similar nominal hole concentration based on a simple charge counting. We do, however, find a pronounced bi-polar phenomenon in thermal conductivity that rapidly increases for Ni-doped samples when temperature is above 600 K. Importantly, Ni-doped samples have higher dimensionless thermoelectric figures of merit values than CeFe4Sb12 over the entire temperature ran...

Preparation of PZT(53/47) thick films deposited by a dip-coating process

Crack-free polycrystalline PZT (PbZrTiO3) thick films up to 15 µm with perovskite structure have been prepared from a dip-coating process. The influence of substrate characteristics, withdrawal speed and ionic concentration of precursor solution on the morphology and microstructure of PZT film was examined. The dielectric, ferroelectric and piezoelectric properties of PZT thick films on Pt/Ti substrate were measured and evaluated. PZT(53/47) thick films on Pt/Ti substrate exhibits a excellent electric properties, e.g. Pr: 35 µC/cm2; Ec: 32 kV/cm; er: 830; tan δ: 0.01-0.03; d33: 142.

Martensitelike spontaneous relaxor-normal ferroelectric transformation in Pb(Zn1∕3Nb2∕3)O3–PbLa(ZrTi)O3 system

The spontaneous relaxor-normal ferroelectric transformation was found in the tetragonal composition of Pb(Zn1∕3Nb2∕3)O3–PbLa(ZrTi)O3 (0.3PZN–0.7PLZT) complex ABO3 system. The corresponding dielectric permittivities and losses of different compositions located near the morphotrophic phase boundary were analyzed. By reviewing all of the results about this type of transformation in previous references, the electric, compositional, structural, and thermodynamic characteristics of the spontaneous relaxor-normal transformation were proposed. Additionally, the adaptive phase model for martensite transformation proposed by Khachaturyan et al. [Phys. Rev. B 43, 10832 (1991)] was introduced into this ferroelectric transformation to explain the unique transformation pathway and associated features such as the tweedlike domain patterns and the dielectric dispersion under the critical transition temperature. Due to the critical compositions near the MPB, the ferroelectric materials just fulfill the condition, in which...

IMPRINT PROPERTIES OF YTTRIUM DOPED PZT THIN FILM

ABSTRACT Undoped and yttrium (Y) doped PZT (40/60) thin films have been deposited by spin-coating on Pt/Ti/SiO2/Si(100) substrates. The yttrium concentration, x, was varied from 1.5 to 3.5 wt% by 0.5 wt%. The annealing temperature and time of the thin films are 550–650°C for 5–10 min in 100% O2 atmosphere. The influence of the yttrium contents on the ferroelectric properties of PZT thin films has been studied. We investigated the imprint properties of Y-doped PZT (40/60) thin films at bias voltage and a temperature of 120°C. It is found that the imprint- resistant properties of the PZT thin films are enhanced by a suitable Y dopant concentration.

Effect of anisotropy on the ferroelectric, optical, and electro-optic properties of PLZT transparent ceramics prepared by uniaxial hot-press sintering techniques

PLZT (X/70/30) ceramics with different La contents (X = 7.45, 7.51,7.57, 7.63) were fabricated to study the effect of anisotropy on ferroelectric, optical, and electro-optic properties in parallel and normal to the uniaxial hot-press sintering direction (abbreviated as parallel and normal), respectively. All samples show the square hysteresis loops but the tetragonality with ferroelectricity is more evident in a parallel direction than that in normal direction. The high transmittances (≥60%, 0.35mm, visible to near infrared light) are obtained. However, the transmittances and the light scattering contrast ratios are higher in the normal direction. The PLZT (7.63/70/30) ceramic exhibits the more stable electrically controlled light scattering behavior in parallel direction and its contrast ratio reaches to the maximum 1.37 in a normal direction in this system.

Magnetic and Electrical Properties of Zr-rich (1-x)PZT+xBiFeO3 Ceramics

We reported multiferroic ceramics (1-x)PZT +xBiFeO3 (x = 0.01–0.10, Zr/Ti = 95/5–100/0) were prepared by a conventional solid-state reaction process. The structures were characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM). XRD showed that the (1-x)PZT+xBiFeO3 samples formed perovskite structure. SEM indicated that the dense ceramics were obtained when the sintering process was modified. It is well known that the PZT95/5 system is a typical ferroelectric material and BiFeO3 possesses antiferromagnetic property. It was found that (1-x)PZT+xBiFeO3 exhibited both ferroelectric and ferromagnetic properties at room temperature. The relationship between the ferroelectric and ferromagnetic properties was discussed.

Fabrication, Microstructure and Magnetic Properties of LiZn Ferrites by Hot Pressing Method

The effects of sintering temperature on microstructure, phase, electrical and magnetic properties of LiZn ferrites prepared by hot pressing methods were examined systematically. All the ferrites were spinel strustures sintered at the temperature above 1050°C. At higher than 1100°C, pores within the grains appeared due to the volatilization of lithium. The DC electrical resistivity ρ increased firstly and decreased dramatically because of the Fe2+ formation. The magnetic properties showed that the saturation magnetization (Ms) increased and coercive field (Hc) decreased with the increasing temperature. The hot pressing method is proven an effective way to obtain the densified LiZn ferrites.

Fabrication and Electrical Properties of Grain-Oriented 0.91Pb(Zn1/3Nb2/3)O3– 0.09PbTiO3 Ceramics

(200) grain-oriented 0.91Pb(Zn1/3Nb2/3)O3–0.09PbTiO3 (PMN–0.09PT) piezoelectric ceramics with a degree of orientation of 0.5052 have been produced from melt by a directional solidification method. The dielectric, ferroelectric, and piezoelectric properties were investigated, e.g., ε~4200, tanδ~0.8%, d33~2100pC/N, kt~58%, and k33~90%, some of these values are comparable to those of ~PZN–PT single crystals. The strain–electric-field curve with a maximum strain of 0.49% at a field of 7kV/cm and well-saturated hysteresis loops with a Pr~32 mC/cm2 were recorded. The results demonstrate that the directional solidification method is a promising technique to fabricate high performance grain-oriented PZN–PT ceramics.

Optical behavior of Pr3+-doped barium titanate-calcium titanate material prepared by sol-gel method

Photoluminescence performances of Pr-doped alkaline-earth titanates (Ba,Ca)TiO3 (with rich barium) prepared by a solgel technique are investigated at room temperature. A relatively strong red luminescence is observed in (Ba0.80Ca0.20)TiO3 material when Pr-BaTiO3 material does not exhibit obvious red luminescence. The phenomenon is discussed with respect to the substitute of Ca and the two-photon luminescence effect. The red luminescence is enhanced by a fast thermal treatment. The wavelength range of luminescence near red and infrared light is broadened by the same process as well. These behaviors are ascribed to the randomization of distribution of Ca and Ba at A site in ABO3 perovskite structure. The experimental results provide not only a possible way to develop new materials with pastel visual impression, but also a potential technique to modify photoluminescence properties that can be controlled by external fields because the microscopic structure of BaTiO3, such as electric domains, can be changed by electric field, temperature, and so on.

Fabrication and characteristics of PLZT thin films derived from MOD process

Crack free PLZT (9/65/35) thin films were prepared by a metallic organic decomposition (MOD) process on Pt(111)/Ti/SiO2/Si(100) and sapphire(001) substrates respectively. The films on Pt/Ti/SiO2/Si substrates present highly (111)-preferred orientation while they display highly (110)-preferred orientation on sapphire substrates. The microstructure of the films were investigated and discussed. Ferroelectric properties of PLZT thin films on Pt/Ti/SiO2/Si(100) substrates have been studied. Typical slim polarization-electric field hysteresis loops were observed. As the film thickness increasing, the remanent polarization Pr increases and the coercive electric field Ec drops. The influence of film thickness on optical transmittance and refractive index nr were examined by the films deposited on sapphire substrates. The nr at 510nm wavelength shows an increasing tendency with film thickness increasing. Great stress aggregated during the film processing is thought to be an important reason which results in the variations of optical properties dependent on the film thickness.