Zhenrong Li

Phase transition and phase stability in [110]-, [001]-, and [111]-oriented 0.68Pb(Mg1/3Nb2/3)O3−0.32PbTiO3 single crystal under electric field

The phase transition and the phase stability in 0.68Pb(Mg1/3Nb2/3)O3–0.32PbTiO3 (PMN-0.32PT) single crystals under different electric fields were investigated over a temperature range from −20 to 200u2009°C using the dielectric property. Crystals with different orientations were used in the research. First, it is found that the intermediate monoclinic or orthorhombic phases are involved in the phase transition from the rhombohedral to tetragonal phase and that the appearance and stability of the intermediate phases as well as the phase path are strongly dependent on factors, such as the history of the sample and the direction and strength of the electric field. The transition behavior from the rhombohedral to tetragonal phase for the samples during the field-heating process is much more complex than that during the field-cooling process. Second, for the ferroelectric-to-paraelectric phase transition, it is found that the dielectric-constant peak actually reflects two processes: one is the ferroelectric relaxo...

Characterization of KNN Single Crystals by Slow-Cooling Technique

Lead free piezoelectric [001]-oriented (K 0.56 Na 0.44 )NbO 3 single crystals with very high crystallization have been grown by slow-cooling technique using 0.8(K 0.5 Na 0.5 )NbO 3 - 0.2K 2 CO 3 powder as starting materials. The dielectric properties, piezoelectric properties and domain structure of KNN single crystals were investigated. Three phase transition temperatures of rhombohedral-to-orthorhombic (R-to-O), orthorhombic-to-tetragonal (O-to-T) and tetragonal-to-cubic (T-to-C) are around −100°C, 214°C and 433°C for KNN single crystal according to the dielectric measurements, respectively. The relationship between dielectric permittivity ϵ and T(above T m ) is very well represented by a Cuire-Weiss law, where the Cuire constant C = 2.44 × 10 5 K and Curie-Weiss temperature T 0 = 647 K (374°C). The average piezoelectric coefficient d 33 of [001]-oriented KNN single crystal is 130pC/N at room temperature. The piezoelectric coefficient d 33 as a function of temperature was studied. The maximum d 33 reached to 220 pC/N around 130°C. Domain structure and the extinction of orthorhombic domain in [001]-oriented KNN single crystal was observed using polarizing light microscope.

MICROSTRUCTURES AND ELECTRICAL PROPERTIES OF PMNT CERAMICS DOPED WITH LITHIUM FLUORIDE

ABSTRACT Microstructures and electrical properties of 0.68Pb(Mg1/3Nb2/3)O3–0.32PbTiO3 (PMNT-0.32PT) ceramics with lithium fluoride additives were investigated. All the samples sintered at 1000°C exhibited the maximum density. LiF plays an important role in the ceramic densification. The dielectric loss of the sample with LiF addition is higher than that of pure PMN-0.32PT ceramic and the samples with LiF addition have more apparent diffusion phase transition than pure PMN-0.32PT sample, all these may be ascribed to anionic (F-O2−) substitution. The lithium fluoride added PMN–0.32PT ceramics sintered at 1000°C have higher piezoelectric constant, which is about 500pC/N.

Polarization reversal and domain kinetics in PMN-30PT single crystals

ABSTRACT Polarization reversal process has been studied in [001]-cut lead magnesium niobate-lead titanate single crystals with 30% lead titanate by in situ visualization of domain kinetics and switching current analysis. It has been shown by high-resolution methods that the sample poling leads to partial decay of as-grown domain structure and decrease of the domain width down to 200 nm. Analysis of the switching current by modified Kolmogorov-Avrami approach has shown that the field dependence of the characteristic time follows activation law with activation field value 1040±50 V/mm. In situ visualization has allowed revealing the main stages of domain structure evolution.

EFFECT OF LITHIUM SALTS ADDITION ON SINTERING TEMPERATURE AND ELECTRICAL PROPERTIES OF PMNT CERAMICS

ABSTRACT The effect of lithium salts (Li2CO3, LiNO3, LiF) addition on sintering temperature and electrical properties of 0.68Pb(Mg1/3Nb2/3)O3-0.32PbTiO3 ceramics were investigated. All the samples with lithium salt additions show a typical liquid phase sintering character. The samples with LiNO3 and LiF addition sintered at 1100°C have dense structure. The dielectric loss decreases for the samples with the Li2CO3 and LiNO3 addition, but increases for the samples with LiF addition. The sample with LiF addition sintered at 1150°C has good piezoelectric properties, which d 33 is 620pC/N and K p is 64%. All these may be attributed to the anionic (F−-O2−) substitution.

The Effect of Ga3+ Substituting Sc3+ on Properties of BiScO3-PbTiO3 Ceramics

0.36(BiSc(1-x)Ga x O3)-0.64PbTiO3(BGSPT64-x, x = 0.001, 0.003, 0.005, 0.008, 0.01, 0.015, 0.02) solid solutions were prepared by conventional solid state reaction method. The results of x-ray diffractions revealed that the introduction of the Ga didnt change the perovskite structure of the solid solutions. The dielectric and piezoelectric properties were investigated. The results showed that BGSPT64-0.01 had an optimized characterization and its piezoelectric coefficient d 33, planar coupling coefficient k p, remnant polarization p r and the coercive field Ec are 510 pC/N, 61%, 49μC/cm2 and 2.1kv/mm, respectively. The BGSPT64-0.01 ceramics will be a good candidate material for the high temperature piezoelectric actuator and transducers.