scholarly journals Oxygen Vacancies in Perovskite Oxide Piezoelectrics

Materials ◽  
2020 ◽  
Vol 13 (24) ◽  
pp. 5596
Author(s):  
Marina Tyunina
Keyword(s):  
Mechanical Properties ◽  
High Temperature ◽  
Chemical Reactions ◽  
Oxygen Vacancies ◽  
Perovskite Oxide ◽  
Semiconductor Physics ◽  
Physical Conditions ◽  
Ferroelectric Behavior ◽  
Piezoelectric Performance ◽  
Mobile Oxygen

The excellent electro-mechanical properties of perovskite oxide ferroelectrics make these materials major piezoelectrics. Oxygen vacancies are believed to easily form, migrate, and strongly affect ferroelectric behavior and, consequently, the piezoelectric performance of these materials and devices based thereon. Mobile oxygen vacancies were proposed to explain high-temperature chemical reactions half a century ago. Today the chemistry-enabled concept of mobile oxygen vacancies has been extrapolated to arbitrary physical conditions and numerous effects and is widely accepted. Here, this popular concept is questioned. The concept is shown to conflict with our modern physical understanding of ferroelectrics. Basic electronic processes known from mature semiconductor physics are demonstrated to explain the key observations that are groundlessly ascribed to mobile oxygen vacancies. The concept of mobile oxygen vacancies is concluded to be misleading.

Boron Nitride Ceramic Composite Obtained by High Pressure and High Temperature Sintering

2012 ◽  
Vol 727-728 ◽  
pp. 736-739 ◽  
Author(s):  
Ana Lucia D. Skury ◽  
Carlos A. Oliveira Monteiro ◽  
Guerold Sergueevitch Bobrovinitchii ◽  
Sérgio Neves Monteiro
Keyword(s):  
Mechanical Properties ◽  
High Pressure ◽  
Composite Material ◽  
High Temperature ◽  
Boron Nitride ◽  
Chemical Reactions ◽  
Ceramic Composite ◽  
Sintering Process ◽  
Polycrystalline Structure ◽  
Binding Agents

In the present work, by selecting Si3N4, TiB2 and Al2O3 as binding agents as well as La3O2 as an additive, sintered wBN composites were studied. By modifying the number of sintering cycles, the composites processed at 4.5GPa and 1800°C showed improved mechanical properties. The degree of transformation of the wBN, as well as the chemical reactions during the sintering process were discussed. This new composite material was found to present polycrystalline structure that provides superior cutting properties. Moreover, owing to superior properties, the wBN composite sharpens itself during cutting.

Toward Switchable Photovoltaic Effect via Tailoring Mobile Oxygen Vacancies in Perovskite Oxide Films

2016 ◽  
Vol 8 (50) ◽  
pp. 34590-34597 ◽  
Author(s):  
Chen Ge ◽  
Kui-juan Jin ◽  
Qing-hua Zhang ◽  
Jian-yu Du ◽  
Lin Gu ◽  
...  
Keyword(s):  
Oxygen Vacancies ◽  
Photovoltaic Effect ◽  
Oxide Films ◽  
Perovskite Oxide ◽  
Mobile Oxygen

Lattice Imaging of Grain Boundaries in Ceramics

1977 ◽  
Vol 35 ◽  
pp. 114-115
Author(s):  
D. R. Clarke ◽  
G. Thomas
Keyword(s):  
Mechanical Properties ◽  
High Temperature ◽  
Silicon Nitride ◽  
Grain Boundaries ◽  
High Temperature Strength ◽  
Current Interest ◽  
Lattice Imaging ◽  
Special Significance ◽  
Structural Applications ◽  
Refractory Ceramics

Grain boundaries have long held a special significance to ceramicists. In part, this has been because it has been impossible until now to actually observe the boundaries themselves. Just as important, however, is the fact that the grain boundaries and their environs have a determing influence on both the mechanisms by which powder compaction occurs during fabrication, and on the overall mechanical properties of the material. One area where the grain boundary plays a particularly important role is in the high temperature strength of hot-pressed ceramics. This is a subject of current interest as extensive efforts are being made to develop ceramics, such as silicon nitride alloys, for high temperature structural applications. In this presentation we describe how the techniques of lattice fringe imaging have made it possible to study the grain boundaries in a number of refractory ceramics, and illustrate some of the findings.

TEM Studies of Grain Boundary Films in Si3N4 Ceramics

1991 ◽  
Vol 49 ◽  
pp. 930-931
Author(s):  
H.-J. Kleebe ◽  
J.S. Vetrano ◽  
J. Bruley ◽  
M. Rühle
Keyword(s):  
Mechanical Properties ◽  
High Temperature ◽  
Silicon Nitride ◽  
Hot Isostatic Pressing ◽  
Amorphous Film ◽  
Liquid Phase Sintering ◽  
Second Phase ◽  
High Temperature Mechanical Properties ◽  
Triple Points ◽  
Boundary Films

It is expected that silicon nitride based ceramics will be used as high-temperature structural components. Though much progress has been made in both processing techniques and microstructural control, the mechanical properties required have not yet been achieved. It is thought that the high-temperature mechanical properties of Si3N4 are limited largely by the secondary glassy phases present at triple points. These are due to various oxide additives used to promote liquid-phase sintering. Therefore, many attempts have been performed to crystallize these second phase glassy pockets in order to improve high temperature properties. In addition to the glassy or crystallized second phases at triple points a thin amorphous film exists at two-grain junctions. This thin film is found even in silicon nitride formed by hot isostatic pressing (HIPing) without additives. It has been proposed by Clarke that an amorphous film can exist at two-grain junctions with an equilibrium thickness.

AEM of reaction-bonded SiC

1992 ◽  
Vol 50 (1) ◽  
pp. 344-345
Author(s):  
K Das Chowdhury ◽  
R. W. Carpenter ◽  
W. Braue
Keyword(s):  
Mechanical Properties ◽  
Phase Transformation ◽  
High Temperature ◽  
Epitaxial Growth ◽  
Liquid Silicon ◽  
Structural Ceramic ◽  
Few Data

Research on reaction-bonded SiC (RBSiC) is aimed at developing a reliable structural ceramic with improved mechanical properties. The starting materials for RBSiC were Si,C and α-SiC powder. The formation of the complex microstructure of RBSiC involves (i) solution of carbon in liquid silicon, (ii) nucleation and epitaxial growth of secondary β-SiC on the original α-SiC grains followed by (iii) β>α-SiC phase transformation of newly formed SiC. Due to their coherent nature, epitaxial SiC/SiC interfaces are considered to be segregation-free and “strong” with respect to their effect on the mechanical properties of RBSiC. But the “weak” Si/SiC interface limits its use in high temperature situations. However, few data exist on the structure and chemistry of these interfaces. Microanalytical results obtained by parallel EELS and HREM imaging are reported here.

ALUMINUM 220

Alloy Digest ◽  
1962 ◽  
Vol 11 (3) ◽  
Keyword(s):  
Mechanical Properties ◽  
Corrosion Resistance ◽  
Shear Strength ◽  
High Temperature ◽  
Heat Treating ◽  
Casting Alloy ◽  
Aluminum Casting ◽  
Aluminum Casting Alloy ◽  
Temperature Performance ◽  
Aluminum Company

Abstract ALUMINUM 220 is a 10% magnesium-aluminum casting alloy having the highest combination of mechanical properties, corrosion resistance and machinability. This datasheet provides information on composition, physical properties, hardness, elasticity, tensile properties, and compressive and shear strength as well as fatigue. It also includes information on high temperature performance and corrosion resistance as well as casting, heat treating, machining, and joining. Filing Code: Al-112. Producer or source: Aluminum Company of America.

ALUMINUM 2011

Alloy Digest ◽  
1978 ◽  
Vol 27 (12) ◽  
Keyword(s):  
Mechanical Properties ◽  
Corrosion Resistance ◽  
Shear Strength ◽  
High Temperature ◽  
Physical Properties ◽  
Copper Alloy ◽  
Heat Treating ◽  
Temperature Performance ◽  
Screw Machine ◽  
Aluminum Copper Alloy

Abstract ALUMINUM 2011 is an age-hardenable aluminum-copper alloy to which lead and bismuth are added to make it a free-machining alloy. It has good mechanical properties and was designed primarily for the manufacture of screw-machine products. This datasheet provides information on composition, physical properties, hardness, elasticity, tensile properties, and shear strength as well as fatigue. It also includes information on high temperature performance and corrosion resistance as well as forming, heat treating, machining, and joining. Filing Code: Al-32. Producer or source: Various aluminum companies. Originally published October 1955, revised December 1978.

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