Point Defects and Cation Diffusion in Cobaltous Oxide

1994 ◽  
Vol 369 ◽  
Author(s):  
Sanjeev Aggarwal ◽  
RÜdiger Dieckmann
Keyword(s):  
Point Defects ◽  
Atmospheric Pressure ◽  
Defect Structure ◽  
Stability Region ◽  
Prior Belief ◽  
Deviation From Stoichiometry ◽  
Point Defect Structure ◽  
O Phase ◽  
Respective Concentration

AbstractThe deviation from stoichiometry, δ, in Co1-δ O was measured in-situ as a function of oxygen activity at temperatures between 1000 and 1400 ºC, using ahigh resolution microbalance. The experiments were conducted over the entire Co1-δO phase stability region at atmospheric pressure. The experimental results were analyzed with regard to the point defect structure and also in comparison with mass and charge transport data. Contrary to prior belief, it was found that the average mobility of the cationic defects and holes varied with their respective concentration.

Point Defects and Diffusion in Nonstoichiometric Metal Oxides

MRS Bulletin ◽  
1991 ◽  
Vol 16 (12) ◽  
pp. 27-32 ◽  
Author(s):  
Rüdiger Dieckmann
Keyword(s):  
Metal Oxides ◽  
Grain Boundaries ◽  
Point Defect ◽  
Point Defects ◽  
Defect Structure ◽  
Ionic Crystals ◽  
Ion Diffusion ◽  
Crystalline Materials ◽  
And Diffusion ◽  
Point Defect Structure

This article briefly reviews the relationships between point defects and ion diffusion in nonstoichiometric ionic crystals, with special emphasis on cubic oxides. It focuses on crystalline materials with negligibly small concentrations of nonequilibrium defects such as dislocations and grain boundaries. First, the concepts used to analyze the point defect structure and the diffusion of ions in nonstoichiometric crystals will be discussed. Then, specific oxides will be considered as examples. These oxides are manganosite, Mn1−ΔO, and spinels of the type Me3−δO4 with Fe and Mn cations, respectively.

Role of point defects in the thermal decomposition of ammonium perchlorate

1968 ◽  
Vol 307 (1490) ◽  
pp. 303-315 ◽  
Keyword(s):  
Electrical Conductivity ◽  
Thermal Decomposition ◽  
Single Crystals ◽  
Ammonium Perchlorate ◽  
Point Defects ◽  
Defect Structure ◽  
Electrical Conductance ◽  
Charge Carriers ◽  
Point Defect Structure

The thermal decomposition of ammonium perchlorate has usually been described in terms of chemical reactions with the point defect structure of the solid ignored. Both the isothermal and adiabatic decompositions have been reinvestigated over the temperature range 200 to 450°C. There is a good correlation between the isothermal d. c. electrical conductance of single crystals, and of conductance as a function of temperature with the extent of decomposition, indicating that charge carriers play a significant role in the thermal decomposition. The study of the electrical conductivity as a function of temperature has resulted in the assignment of a probable defect structure to ammonium perchlorate: cationic Frenkel type below 250°C and Schottky disorder at higher temperatures. This suggests an explanation for the phenomenon of only 30% decomposition below 250°C and 100% above this temperature.

Theoretical investigation of defect structure in B2 TrSc (Tr =Cd, Ru) alloys

2015 ◽  
Vol 29 (35n36) ◽  
pp. 1550234 ◽  
Author(s):  
Aissam Hidoussi ◽  
Aissa Belgacem-Bouzida ◽  
Maria Helena Braga ◽  
Haroun Righi
Keyword(s):  
Experimental Data ◽  
Point Defect ◽  
Point Defects ◽  
Defect Structure ◽  
Defect Formation ◽  
Random Structure ◽  
Formation Enthalpies ◽  
Thermal Defect ◽  
Point Defect Structure ◽  
Schottky Model

Point defect structure of B2 TrSc (Tr[Formula: see text]Cd, Ru) alloys was investigated using supercell and special quasi-random structure (SQS) approaches. According to our results, Tr and Sc anti-sites are the constitutional point defects in Tr-rich and Sc-rich B2 TrSc, respectively. To investigate the thermal defect concentrations at finite temperatures, we adopted the Wagner–Schottky model using point defect formation enthalpies obtained from supercell and SQS approaches. The present results suggest that the predominant thermal defects in B2 CdSc are of exchange type, and in B2 RuSc are of interbranch Sc type. The calculated results show an agreement with the available theoretical and experimental data.

The Influence of Li on the Point Defect Structure of ZnO Varistor Ceramics

2014 ◽  
Vol 1004-1005 ◽  
pp. 424-428
Author(s):  
Lei Zhao ◽  
Peng Fei Cheng
Keyword(s):  
Dielectric Properties ◽  
Oxygen Vacancy ◽  
Point Defect ◽  
Point Defects ◽  
Defect Structure ◽  
Wide Band ◽  
Lithium Content ◽  
Zno Varistor ◽  
Zinc Interstitial ◽  
Point Defect Structure

In this paper, the dielectric properties of ZnO-Bi2O3 based varistor ceramics doped with Li are investigated by Novocontrol wide band dielectric spectrometer. It is found that Lithium is an amphoteric impurity. If the content of Lithium is very low, It will enters into the interstitials and Lithium interstitial is formed as a donor. While with the increase of Lithium content, Zn is replaced with Li and Lithium substitution for Zinc as a acceptor is formed. If the content of Lithium increases further, Lithium interstitial is formed again with the redundant Lithium. Therefore, the concentrations of intrinsic point defects of Zinc interstitial and oxygen vacancy varies with the content of Lithium, which leads to the increase of Schottky barrier at grainboundary with Lithium.

Innovative Closed-Cell Reactor Permits In Situ Heating and Gas Reactions with Atomic Resolution at Atmospheric Pressure

2012 ◽  
Vol 18 (S2) ◽  
pp. 1118-1119 ◽  
Author(s):  
L. Allard ◽  
S.H. Overbury ◽  
M.B. Katz ◽  
W.C. Bigelow ◽  
D. Nackashi ◽  
...  
Keyword(s):  
Atmospheric Pressure ◽  
Atomic Resolution ◽  
Closed Cell ◽  
Cell Reactor ◽  
In Situ Heating ◽  
Gas Reactions

Extended abstract of a paper presented at Microscopy and Microanalysis 2012 in Phoenix, Arizona, USA, July 29 – August 2, 2012.

Non-Stoichiometry and Cation Tracer Diffusion Studies in the Magnetite-UlvÖSpinel Solution, (Fe,Ti)3-δO4

1994 ◽  
Vol 369 ◽  
Author(s):  
Sanjeev Aggarwal ◽  
Rudiger Dieckmann
Keyword(s):  
Diffusion Coefficients ◽  
Tracer Diffusion ◽  
Oxygen Activity ◽  
Spinel Solid Solution ◽  
Low Oxygen ◽  
Cation Diffusion ◽  
Deviation From Stoichiometry ◽  
Diffusion Studies ◽  
Tracer Diffusion Coefficients ◽  
Point Defect Structure

AbstractCation diffusion in the spinel solid solution (Fe1-xTix)3-δO4 (0≤ x ≤ 0.3) was investigated at 1200 ºC as a function of oxygen activity, aO2 and cationic composition, x. At different cationic compositions, cation tracer diffusion coefficients, D*Me of Me = Fe and Ti were measured as a function of oxygen activity. Plots of log DMe vs. loga0 show V-shaped curves, indicating that different types of point defects prevail at high anc low oxygen activities. Thermogravimetric experiments were conducted, using a high resolution microbalance, to determine the deviation from stoichiometry in (Fe1-xTix)3-δO4 at 1200 °C. δversus log aO2 curves are S-shaped. An analysis of the oxygen activity dependences of thecation diffusion coefficients and the deviation from stoichiometry with regardto the point defect structure suggests that at high oxygen activities cation vacancies are the predominant defects governing the deviation from stoichiometry and the diffusion ofcations. At low oxygen activities, and at small values of x, cation interstitials determine the deviation from stoichiometry, while they dominate for 0 ≤ x ≤ 0.3 inthe cation diffusion.

Hg1-xCdxTe: Defect Structure Overview

1990 ◽  
Vol 216 ◽  
Author(s):  
M.A. Berding ◽  
A. Sher ◽  
A.-B. Chen
Keyword(s):  
Point Defects ◽  
Defect Structure ◽  
Defect Formation ◽  
Activation Energies ◽  
Mass Action ◽  
Native Defect ◽  
Native Point Defects ◽  
Vacancy Migration ◽  
Formation Energies ◽  
Diffusion Activation

ABSTRACTNative point defects play an important role in HgCdTe. Here we discuss some of the relevant mass action equations, and use recently calculated defect formation energies to discuss relative defect concentrations. In agreement with experiment, the Hg vacancy is found to be the dominant native defect to accommodate excess tellurium. Preliminary estimates find the Hg antisite and the Hg interstitial to be of comparable densities. Our calculated defect formation energies are also consistent with measured diffusion activation energies, assuming the interstitial and vacancy migration energies are small.

scholarly journals A Novel Lithium Foil Cosmic-Ray Neutron Detector for Measuring Field-Scale Soil Moisture

2021 ◽  
Vol 3 ◽  
Author(s):  
Andres Patrignani ◽  
Tyson E. Ochsner ◽  
Benjamin Montag ◽  
Steven Bellinger
Keyword(s):  
Soil Moisture ◽  
Water Content ◽  
Atmospheric Pressure ◽  
Lower Cost ◽  
Cosmic Ray ◽  
Absolute Difference ◽  
Atmospheric Conditions ◽  
Volumetric Soil Water Content ◽  
The Mean

During the past decade, cosmic-ray neutron sensing technology has enabled researchers to reveal soil moisture spatial patterns and to estimate landscape-average soil moisture for hydrological and agricultural applications. However, reliance on rare materials such as helium-3 increases the cost of cosmic-ray neutron probes (CRNPs) and limits the adoption of this unique technology beyond the realm of academic research. In this study, we evaluated a novel lower cost CRNP based on moderated ultra-thin lithium-6 foil (Li foil system) technology against a commercially-available CRNP based on BF3 (boron trifluoride, BF-3 system). The study was conducted in a cropped field located in the Konza Prairie Biological Station near Manhattan, Kansas, USA (325 m a.s.l.) from 10 April 2020 to 18 June 2020. During this period the mean atmospheric pressure was 977 kPa, the mean air relative humidity was 70%, and the average volumetric soil water content was 0.277 m3 m−3. Raw fast neutron counts were corrected for atmospheric pressure, atmospheric water vapor, and incoming neutron flux. Calibration of the CRNPs was conducted using four intensive field surveys (n > 120), in combination with continuous observations from an existing array of in situ soil moisture sensors. The time series of uncorrected neutron counts of the Li foil system was highly correlated (r2 = 0.91) to that of the BF-3 system. The Li foil system had an average of 2,250 corrected neutron counts per hour with an uncertainty of 2.25%, values that are specific to the instrument size, detector configuration, and atmospheric conditions. The estimated volumetric water content from the Li foil system had a mean absolute difference of 0.022 m3 m−3 compared to the value from the array of in situ sensors. The new Li foil detector offers a promising lower cost alternative to existing cosmic-ray neutron detection devices used for hectometer-scale soil moisture monitoring.

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