scholarly journals Influence of rare-earth additives (La, Sm and Dy) on the microstructure and dielectric properties of doped BaTiO3 ceramics

2010 ◽  
Vol 42 (1) ◽  
pp. 69-79 ◽  
Author(s):  
Vesna Paunovic ◽  
Lj. Zivkovic ◽  
V. Mitic
Keyword(s):  
Phase Transformation ◽  
Room Temperature ◽  
Core Shell ◽  
Homogeneous Microstructure ◽  
Grain Sizes ◽  
Air Atmosphere ◽  
Fine Grain ◽  
Heavily Doped ◽  
Core Shell Structure ◽  
Diffuse Phase

A series of La/Mn, Sm/Mn and Dy/Mn codoped BaTiO3 samples were prepared by the conventional solid state procedure with dopant concentrations ranging from 0.1 up to 2.0 at%. The specimens were sintered at 1320?C and 1350?C in an air atmosphere for two hours. The low doped samples demonstrated a mainly uniform and homogeneous microstructure with average grain sizes ranging from 0.3 ?m to 5.0 ?m. The appearance of secondary abnormal grains in the fine grain matrix and core-shell structure were observed in highly doped La/BaTiO3 and Dy/BaTiO3 sintered at 1350?C. The low doped samples, sintered at 1350?C, display a high value of dielectric permittivity at room temperature, 6800 for Sm/BaTiO3, 5900 for Dy/BaTiO3 and 3100 for La/BaTiO3. A nearly flat permittivity-response was obtained in specimens with 2.0 at% additive content. Using a modified Curie-Weiss law the Curie-like constant C? and a critical exponent ? were calculated. The obtained values of ? pointed out the diffuse phase transformation in heavily doped BaTiO3 samples.

A mesoporous Ni3N/NiO composite with a core–shell structure for room temperature, selective and sensitive NO2 gas sensing

RSC Advances ◽  
2016 ◽  
Vol 6 (49) ◽  
pp. 42917-42922 ◽  
Author(s):  
Mingming Zou ◽  
Hu Meng ◽  
Fengdong Qu ◽  
Liang Feng ◽  
Minghui Yang
Keyword(s):  
Shell Structure ◽  
Room Temperature ◽  
Gas Sensing ◽  
Core Shell ◽  
Template Free ◽  
Core Shell Structure

Mesoporous Ni3N/NiO composites with core–shell structure were synthesized by a template free method, demonstrate a significant improvements both in sensitivity and in selectivity for NO2 gas sensing at room temperature.

Au@ZnO core–shell structure for gaseous formaldehyde sensing at room temperature

2014 ◽  
Vol 199 ◽  
pp. 314-319 ◽  
Author(s):  
Feng-Chao Chung ◽  
Zhen Zhu ◽  
Peng-Yi Luo ◽  
Ren-Jang Wu ◽  
Wei Li
Keyword(s):  
Shell Structure ◽  
Room Temperature ◽  
Core Shell ◽  
Formaldehyde Sensing ◽  
Core Shell Structure ◽  
Gaseous Formaldehyde

Core-Shell Structure of Intermediate Precipitates in a Nb-Based Z-Phase Strengthened 12% Cr Steel

2017 ◽  
Vol 23 (2) ◽  
pp. 360-365 ◽  
Author(s):  
Masoud Rashidi ◽  
Hans-Olof Andrén ◽  
Fang Liu
Keyword(s):  
Phase Transformation ◽  
Shell Structure ◽  
Atom Probe Tomography ◽  
Atom Probe ◽  
Core Shell ◽  
The Core ◽  
The Matrix ◽  
Core Shell Structure ◽  
Cr Steels

AbstractIn creep resistant Z-phase strengthened 12% Cr steels, MX (M=Nb, Ta, or V, and X=C and/or N) to Z-phase (CrMN, M=Ta, Nb, or V) transformation plays an important role in achieving a fine distribution of Z-phase precipitates for creep strengthening. Atom probe tomography was employed to investigate the phase transformation in a Nb-based Z-phase strengthened trial steel. Using iso-concentration surfaces with different concentration values, and subtracting the matrix contribution enabled us to reveal the core-shell structure of the transient precipitates between MX and Z-phase. It was shown that Z-phase forms by diffusion of Cr into NbN upon ageing, and Z-phase has a composition corresponding to Cr1+xNb1−xN with x=0.08.

A BIO-INSPIRED POLYDOPAMINE APPROACH TO PREPARATION OF GOLD-COATED Fe3O4 CORE–SHELL NANOPARTICLES: SYNTHESIS, CHARACTERIZATION AND MECHANISM

NANO ◽  
2013 ◽  
Vol 08 (06) ◽  
pp. 1350061 ◽  
Author(s):  
PENG AN ◽  
FANG ZUO ◽  
XINHUA LI ◽  
YUANPENG WU ◽  
JUNHUA ZHANG ◽  
...  
Keyword(s):  
Shell Structure ◽  
Room Temperature ◽  
Core Shell ◽  
Shell Nanoparticles ◽  
Stabilizing Agent ◽  
X Ray ◽  
Transmission Electron ◽  
Core Shell Structure ◽  
Core Shell Nanoparticles

A biomimetic and facile approach for integrating Fe 3 O 4 and Au with polydopamine (PDA) was proposed to construct gold-coated Fe 3 O 4 nanoparticles ( Fe 3 O 4@ Au – PDA ) with a core–shell structure by coupling in situ reduction with a seed-mediated method in aqueous solution at room temperature. The morphology, structure and composition of the core–shell structured Fe 3 O 4@ Au – PDA nanoparticles were characterized by transmission electron microscopy (TEM), X-ray powder diffraction (XRD) and X-ray photoelectron spectrometry (XPS). The formation process of Au shell was assessed using a UV-Vis spectrophotometer. More importantly, according to investigating changes in PDA molecules by Fourier transform infrared spectroscopy (FTIR) and in preparation process of the zeta-potential data of nanoparticles, the mechanism of core–shell structure formation was proposed. Firstly, PDA-coated Fe 3 O 4 are obtained using dopamine (DA) self-polymerization to form thin and surface-adherent PDA films onto the surface of a Fe 3 O 4 "core". Then, Au seeds are attached on the surface of PDA-coated Fe 3 O 4 via electrostatic interaction in order to serve as nucleation centers catalyzing the reduction of Au 3+ to Au 0 by the catechol groups in PDA. Accompanied by the deposition of Au , PDA films transfer from the surface of Fe 3 O 4 to that of Au as stabilizing agent. In order to confirm the reasonableness of this mechanism, two verification experiments were conducted. The presence of PDA on the surface of Fe 3 O 4@ Au – PDA nanoparticles was confirmed by the finding that glycine or ethylenediamine could be grafted onto Fe 3 O 4@ Au – PDA nanoparticles through Schiff base reaction. In addition, Fe 3 O 4@ Au – DA nanoparticles, in which DA was substituted for PDA, were prepared using the same method as that for Fe 3 O 4@ Au – PDA nanoparticles and characterized by UV-Vis, TEM and FTIR. The results validated that DA possesses multiple functions of attaching Au seeds as well as acting as both reductant and stabilizing agent, the same functions as those of PDA.

scholarly journals Strengthening of Nanocrystalline Al with Al3Zr Core-Shell Structure

Metals ◽  
2020 ◽  
Vol 10 (9) ◽  
pp. 1144
Author(s):  
Dora Janovszky
Keyword(s):  
Mechanical Properties ◽  
Shell Structure ◽  
Hot Pressing ◽  
Room Temperature ◽  
High Energy ◽  
Core Shell ◽  
Mixed Powder ◽  
Reinforcing Particles ◽  
Core Shell Structure ◽  
Nanocrystalline Phases

High-density Al-based composites reinforced with ten-wt.% recycled nanocrystalline CuZrAgAl particles have been fabricated by mechanical milling, cold- and hot-pressing. The microstructures, phase transformations, and mechanical properties of the mixed powder and sintered samples were investigated. After milling in a ball mill for 30 h, the microhardness of the mixed powder increases to 301 ± 31 HV0.01 and 222 ± 10 HV0.01 without and with ethanol milling, respectively. On account of the interdiffusion, the melting temperature of mixed powder reduces to 574 ± 5.0 °C and 627.5 ± 6.5 °C after 30 h milling. The study showed that the reinforcing particles are homogeneously distributed in the sintered nanocrystalline Al-based composites. During the hot-pressing, a shell zone forms at the interface of reinforcing particles during hot pressing after high energy milling with a minimum of ten hours milling time. This shell zone consists of Al3Zr (D023) phase. The coarsening resistant core-shell structure and grain refinement greatly improve mechanical properties. The compression strength at room temperature varies between 650 and 800 MPa at room temperature and is 380 MPa at 400 °C for the composite containing ten-wt.% of the Cu-Zr-based amorphous-nanocrystalline phases. The Brinell hardness of the sintered composite is 329 HB.

scholarly journals Electrical characteristics of Er doped BaTiO3 ceramics

2017 ◽  
Vol 49 (2) ◽  
pp. 129-137 ◽  
Author(s):  
Vesna Paunovic ◽  
Vojislav Mitic ◽  
Milos Djordjevic ◽  
Milos Marjanovic ◽  
Ljubisa Kocic
Keyword(s):  
Electrical Resistivity ◽  
Temperature Response ◽  
Sem Analysis ◽  
Electrical Characteristics ◽  
Conventional Solid State Reaction ◽  
Homogeneous Microstructure ◽  
Temperature Range ◽  
Grain Sizes ◽  
Air Atmosphere ◽  
Er Doped

In this study, the electrical resistivity (?) and PTC effect of Er doped BaTiO3 ceramics are investigated. The concentrations of Er2O3 in the doped samples vary from 0.01 to 1.0 at% Er. The samples are prepared by the conventional solid state reaction, and sintered at 1320? and 1350?C in air atmosphere for 4 hours. The SEM analysis shows that all of measured samples are characterized by polygonal grains. The uniform and homogeneous microstructure with grain sizes from 20 to 45?m is the main characteristic of the low doped samples (0.01 and 0.1 at% Er). For the samples doped with the higher dopant concentration (0.5 and 1.0 at%) the average grains sizes have been ranged from 5 to 10 ?m. The electrical resistivity is measured in the temperature range from 25?C to 170?C, at frequencies 1 kHz, 10 kHz and 100 kHz. The electrical resistivity values, measured at frequency of 1 kHz and room temperature, have been ranged from 1.62?104 ?cm to 4.24?104 ?cm, for samples sintered at 1320?C and from 1.43?104 ?cm to 1.94?104 ?cm, for samples sintered at 1350?C. A nearly flat and stable electrical resistivity-temperature response is characteristic for all samples at the temperature range from 25?C to 120?C. Above this temperature, the electrical resistivity increases rapidly. At 170?C the value of electrical resistivity is ranged 9.84?104 ?cm -1.62?105 ?cm, for Tsin=1320?C, and 6.11?104 ?cm 1.32?105 ?cm, for Tsin=1350?C. The electrical resistivity decreases with concentration increment up to 0.5 at%, while above 0.5 at% it increases. Also, with increasing frequency, ? decreases for a few orders of magnitude.

Visualizing a core–shell structure of heavily doped silicon quantum dots by electron microscopy using an atomically thin support film

Nanoscale ◽  
2018 ◽  
Vol 10 (16) ◽  
pp. 7357-7362 ◽  
Author(s):  
Hiroshi Sugimoto ◽  
Masataka Yamamura ◽  
Makoto Sakiyama ◽  
Minoru Fujii
Keyword(s):  
Electron Microscopy ◽  
Transmission Electron Microscopy ◽  
Shell Structure ◽  
Core Shell ◽  
Oxide Support ◽  
Si Quantum Dot ◽  
Transmission Electron ◽  
Doped Silicon ◽  
Heavily Doped ◽  
Core Shell Structure

We successfully visualize a core–shell structure of a heavily B and P codoped Si quantum dot (QD) by transmission electron microscopy using an ultra-thin graphene oxide support film.

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