Yong-Ling Wang

Dielectric properties of Ba0.6Sr0.4TiO3∕Mg2SiO4∕MgO composite ceramics

The dielectric properties of BSTO∕Mg2SiO4∕MgO composite ceramics have been investigated systematically. The dielectric properties of BSTO composites under a dc bias field can be interpreted by the “soft-mode” theory near the phase transition and Johnson’s phenomenological equation far above the transition temperature. Compared with most of the other BSTO composite ceramics, BSTO∕Mg2SiO4∕MgO not only can be sintered at a lower temperature but also keep a higher dielectric tunability versus a lower dielectric constant. For example, BSTO∕35wt.%Mg2SiO4∕15wt.%MgO has a dielectric tunability ∼13.18% (under 2kV∕mm biasing) versus a dielectric constant er(0)∼118.40 at 25°C. It suggests that the dielectric properties are influenced to a great extent by the microstructure, and the dielectric tunability is enhanced when more continuous BSTO phase is obtained.

Structural and magnetic properties of NdFe12−xMoxN1−δ compounds

A series of nitrides NdFe12−xMoxNi1−δ with x=1–2.5 and δ≤0.2 have been investigated. All nitrides are of the ThMn12 tetragonal structure with the unit cell volumes about 3% larger than their parent alloys. Curie temperatures are enhanced by nitrogenation about 160 K and increase linearly with decreasing content x of Mo. NdFe12−xMox exhibits a weak uniaxial anisotropy with a value of BA less than 0.6 T when x≥1.75. After nitrogenation, all nitrides have a strong uniaxial anisotropy. Values of the anisotropy field BA increase monotonically from 6.35 T for x=2.5 up to 9.5 T for x=1 as decreasing content x of Mo. Saturation magnetizations also increase monotonically with decreasing content x.

Microstructure and mechanical properties of small amounts of In2O3 reinforced Pb(ZrxTi1−x)O3 ceramics

Piezoelectric Pb(Zr{sub x}Ti{sub 1-x})O{sub 3} (PZT) ceramics with small amount (0.5-2.0 wt.%) of In{sub 2}O{sub 3} are prepared by conventional sintering method. Based on X-ray diffraction analysis, the tetragonality of PZT matrix decreases with In{sub 2}O{sub 3} content, indicating that In{sub 2}O{sub 3} diffuses into PZT matrix. The microstructure of PZT matrix is significantly refined by doping small amounts of In{sub 2}O{sub 3}. The grain size reduction and the matrix grain boundary reinforcement are the probable mechanism responsible for the high strength and hardness in the PZT/In{sub 2}O{sub 3} materials. The enhancement in Youngs modulus is attributed to In{sup 3+} substitution. The decreased tetragonality with In{sub 2}O{sub 3} addition results in less crack energy absorption by domain switching and, hence, causes the small reduction in fracture toughness.

Internal friction of nanocrystalline silver

Low frequency internal friction and shear modulus of nanocrystalline silver were measured by both force vibration and free decay methods. The specimens were prepared by inert gas condensation and in situ warm compaction. The average grain size of the specimens was 52 nm. An internal friction peak was observed around 450 K. The activation energy of the peak was measured to be 0.88 (±0.1) eV, in agreement with that of grain boundary diffusion in silver. The internal friction peak is suggested to be associated with grain boundary relaxation.

Dielectric Breakdown Properties of Zr-Rich Lead Zirconate Titanate Ceramics

The series Nb-doped zirconate-rich lead zirconate titanate (PZT) ceramics with high densities up to 97% were fabricated using the traditional solid reaction method. We investigated the dielectric breakdown strength of the series PZT ceramics and detected first that the dielectric breakdown strength increased with an increase in Zr/Ti at the boundary of the antiferroelectric and ferroelectric phases. A qualitative analysis was carried out to discuss the observed phenomena. The relationship between dielectric breakdown and microstructure was also discussed.

Preparation and Internal Friction of Nanoscale Gallium Droplets

A simple but effective method, ultrasonic vibration, has been used to prepare the nanoscale (hereafter n-) Ga droplets. The n-Ga droplets with average particle size of about 60-80 nm in diameter dispersed in polystyrenes (PS) have been successfully obtained. The low frequency internal friction of solid polystyrenes containing n-Ga droplets was measured. We observed for the first time, that the internal friction peak caused by n-Ga droplets appears around 313 K. The peak shifts to higher temperature with increasing frequency, indicating a relaxation peak. It is suggested that the internal friction peak is associated with the relaxation of n-Ga droplets in the cavities of matrix under applied stress.