Jianmin Zhu

The microstructure studies of bismuth sulfide nanorods prepared by sonochemical method

In this work, the microstructures of Bi2S3 single crystal nanorods were investigated by transmission electron microscopy (TEM), selected area electron diffraction (SAED) and high-resolution transmission electron microscopy (HREM) in detail. The mechanism of the formation of Bi2S3 nanorods prepared by a sonochemical method is explored.

Microstructures of the monomorph piezoelectric ceramic actuators with functional gradients

Abstract In this paper, a monolithic ceramic bar with a gradient of piezoelectric activity across its thickness is introduced, which is fabricated by interdiffusion between a high piezoelectric and dielectric compositions. The microstructures of the interdiffusion layer have great effects on the electric field-induced displacement characteristics and interfacial strength of the monomorph piezoelectric actuator. The compositional profiles, phase distributions, and short-range phenomena in the interdiffusion layer formed in the PZT/PNN (PbNi 1/3 Nb 2/3 O 3 : PNN) monomorph ceramic actuators with functional gradients are investigated by electron probe microbeam analyses (EPMA) and transmission electron microscopy (TEM), respectively. The results show that the thickness of the interdiffusion layer ( d ) can be ordered as d Ni 2+ > d Nb 5+ > d Ti 4+ > d Zr 4+ . An interface between the rhombohedral and pseudocubic phases is found to exist in the interdiffusion layer by TEM observations and selected area electron diffraction (SAED) patterns. The SAED studies also reveal the presence of the 1/2 [111] superlattice spots along the [111] direction of perovskite cubic unit cell, and the origin of the superlattice is discussed.

Carbon clusters in N-doped ZnO by metal-organic chemical vapor deposition

We employed transmission electron microscopy and Raman spectra to investigate the behavior of impurity carbon usually unintentionally introduced in N-doped ZnO by metal-organic chemical vapor deposition. Unintentional doped carbon may form graphite clusters along grain boundaries resulting in n-type domains and possibly be a big obstacle for the realization of p-type conductivity. The enhanced desorption rate of hydrocarbon radicals by high temperature and oxygen atom will significantly suppress carbon incorporation rate. The results provide understandings of the formation mechanism of carbon clusters and help us find some available routines to minimize carbon impurity for realization of p-type N-doped ZnO.

Dissociation of grain boundary dislocations in SrBi2Ta2O9 ferroelectric thin films

In this work, the dissociation of grain boundary dislocations (GBDs) is reported in SrBi2Ta2O9 (SBT) ferroelectric thin films with c-axis orientation grown by pulsed-laser deposition on Pt/TiO2/SiO2/Si(100) substrates. Small-angle (8.2°) [001] tilt grain boundaries with a boundary plane close to the (110) plane exhibit partial GBDs separated by stacking faults. The dissociated grain-boundary structures have twice the number of GBDs and interdislocation core channel width smaller than that Frank’s geometrical rule predicts. At the equilibrium, the repulsive elastic force between partial dislocations is balanced by an attractive force produced by the formation of a stacking fault between the partials. Based on this, the stacking fault energy is evaluated to be 0.27–0.29 J/m2. The relationship between the leakage current of SBT films and dissociation of GBDs is also discussed.

EPMA and TEM investigations on the interdiffusion layer of the PNN/PZT functionally gradient piezoelectric ceramics

The compositional profile, distribution of the phases and the ordering behavior in the interdiffusion layer of the PNN/PZT functionally gradient piezoelectric ceramics have been investigated by electron probe microbeam analyses (EPMA) and transmission electron microscopy (TEM) respectively. The results show that the thickness of the interdiffusion layers (d) for Ni2+, Nb5+, Ti4+ and Zr4+ ions are ordered as dNi2+ > dNb5+ > dTi4+ > dZr4+. It is demonstrated by TEM observation and selected area electron diffraction (SAED) patterns that a clear interface between the rhombohedral and pseudocubic phases exists in the interdiffusion layer. The SAED studies also reveal the presence of F spots along the [111] direction of the perovskite cubic unit cell. The origin of this superstructure is determined.

Actuators, piezoelectric ceramics and functionally gradient materials

Abstract Piezoelectric ceramic actuators and materials play a key role in the development of advanced precision engineering. The breakthroughs in this field are closely related to the development of various types of piezoelectric ceramic actuators and related materials. The likelihood that the range of applications and demand for actuators will grow quickly has stimulated intensive researches on piezoelectric ceramics. Functionally gradient materials (FGMs) are new classes of composites characterized by compositional and/or microstructural gradation over macroscopic/microscopic distances. This constitutional gradation can be tailored to meet specific needs while providing the best utilization of composite components. Furthermore, FGMs technology is also a novel interfacial technology to solve the problems associated with the sharp interface between two dissimilar materials. In recent years significant advances in the development of FGMs have been achieved. In this paper, we first briefly review the recent progress of ceramic actuators and developments of piezoelectric materials, and then focus on summarizing typical applications of functional gradients in piezoelectric and ferroelectric materials.

Domain structures and planar defects in SrBi2Ta2O9 single crystals observed by transmission electron microscopy

In this work, the domain structures and structural planar defects in SrBi2Ta2O9 (SBT) single crystals with (001) orientation were investigated by transmission electron microscopy. The 90° domain walls are identified by the 90° rotation relationship of the electron diffraction pattern about the [001] zone axis, and which exhibit irregular configurations. Antiphase boundaries (APBs) in SBT single crystals are also observed, which exhibit ribbon-like morphologies. Fourfold vertices formed by four APBs meeting together are observed as predominant singularities, and are explained by a four-state clock model, in which the four states are considered as the TaO6 octahedra tilting left, right, forward, or backward along the crystallographic directions. Some threefold vertices are also observed since both threefold and fourfold vertices are energetically allowed in the present model.

Ge-dot/Si multilayered structures through Ni-induced lateral crystallization

We demonstrate a method for fabricating high-quality Ge-dot/Si multilayered structures. High-density self-assembled Ge dots are grown on amorphous Si layer periodically by low-pressure chemical vapor deposition, and then the amorphous Si are crystallized through Ni-based metal-induced lateral crystallization. Optical microscopy, micro-Raman spectroscopy, and electron microscopy observations reveal that the crystallized Si film has large leaflike grains elongated along the lateral crystallization direction, which shows (110) preference. Furthermore, this preference is found to deliver to different Si layers. The strain shift of Ge dots deduced from Raman spectroscopy reveals a formation of a high-quality interface between the crystallized Si and Ge dot.

Configurations of ferroelectric domains in bismuth- and Zinc-modified Pb(Ni_1/3Nb_2/3)O_3-PbTiO_3-PbZrO_3 ceramics

Transmission electron microscopy was used to investigate the domain structures of the (Pb0.985Bi0.01)(Ni1/4Zn1/12Nb2/3)0.2(Zr_σTi1-σ)0.8O3 (0.30 ≤ σ ≤ 0.70) ceramics, which are located in the ferroelectric tetragonal and rhombohedral phase regions, and also near the morphotropic phase boundary (MPB). The results show that the lamellar twinning domains and the δ-fringe contrast are most frequently observed in the compositions located in the ferroelectrc tetragonal phase region. In the compositions near the MPB, a banded domain structure similar to herringbone pattern is observed, which contains many parallel bands forming 90° or 70° angles whereas they are inconsistent with one another on both sides of the herringbone domain patterns. The morphology of the herringbone domain structure observed in the bismuth- and zinc-modified PNN-PZ-PT ceramics with composition near the MPB can be described by a space-stacking succession of two crystallographically equivalent plates whereas made from different twin-related domains, with the same habit plane parallel to the (011)-type plane. In the compositions located in the rhombohedral phase region, the stripelike domains are observed, and a local random contrast representing short-range-ordered ‘island’-typed polar clusters or nanodomains is also found, which is attributed to the existence of the polar microregions with the dispersed nanometer-sized short-range-ordered domains in the rhombohedral matrix, because the free energy of the ensembl e of the polar microregion is lowered, and the relative thermodynamic stability is increased with increasing the content ratio of Zr to Ti. In addition, the wavy character in the thickness fringe is commonly observed at the fringe of thin foil, which is due to continuous bending of the thin foil at various equivalent directions.

Saed and tem investigations of domain structure in bismuth-and zinc-modified Pb(M1/3Nb2/3)O3-PbTiO3-PbZrO3 ceramics at morphotropic phase boundary

Abstract Transmission electron microscopy and electron diffraction investigations of the ferroelectric domain structures in the Bi-and Zn-modified Pb(Ni1/3Nb2-3)O3-PbTiO3-PbZrO3 (PNN-PT-PZ) ceramics at the morphotropic phase boundary (MPB) revealed the triplet splitting of electron diffraction spots due to the coexistence of the tetragonal (T 1 and T 2) and rhombohedral (R) phases at the microscopic ferroelectric-domain level. The angular values formed between the parallel stripes in the herringbone domain pattern can be explained by a model of spatial domain configuration previously proposed for BaTiO3 ceramics. A succession model of ferroelectric domain structures T 1 RT 2 RT 1… is proposed to explain the coexistence of T and R phases in the same ceramic grain at the MPB. The elastically stored energy in the mixed T-R wall was estimated, and its uniform distribution confirms this succession model.