Ni-Substitution Induced Inversion in ZnFe2O4 Seen by Positron Annihilation

2012 ◽  
Vol 733 ◽  
pp. 219-223 ◽  
Author(s):  
P.M.G. Nambissan ◽  
O. Mondal ◽  
C. Chakrabarty ◽  
M. Pal
Keyword(s):  
Positron Annihilation ◽  
Spinel Structure ◽  
Positron Lifetime ◽  
Drastic Change ◽  
Doppler Broadening ◽  
Positron Trapping ◽  
Normal Spinel ◽  
Ni Substitution ◽  
Positron Lifetimes ◽  
Coincidence Doppler Broadening

We report in this work about the inversion of the spinel structure of ZnFe2O4induced by the substitution of Zn2+by Ni2+ions. Positron lifetimes were measured in Zn1-xNixFe2O4with different concentrations (x) of doped Ni2+ions and a drastic change across x = 0.4 – 0.6 was observed, which is attributed to this transformation. The interchange of positions of the cations on doping leaves a fraction of them unoccupied and these vacancies act as positron trapping centres. Since Ni2+is smaller in size than Zn2+, defects due to non-stoichiometry are less in NiFe2O4than in ZnFe2O4. The increase in positron lifetime implies the trapping of positrons being shifted from A- to B-sites and is an indication of the transformation from inverse to normal spinel configuration. Coincidence Doppler broadening measurements supported these findings.

Positron Annihilation Studies on La1-xSrxMnO3 Manganites

2017 ◽  
Vol 373 ◽  
pp. 201-204
Author(s):  
Yu Yang Huang ◽  
Yan Meng ◽  
Wen Hua Huang ◽  
Shou Lei Xu ◽  
Ding Kang Xiong ◽  
...  
Keyword(s):  
Curie Temperature ◽  
Positron Annihilation ◽  
Electron Density ◽  
Exchange Coupling ◽  
Positron Lifetime ◽  
Double Exchange ◽  
Ferromagnetic Coupling ◽  
Doppler Broadening ◽  
Doppler Broadening Spectra ◽  
Coincidence Doppler Broadening

Positron lifetime and coincidence Doppler broadening spectra of La1-xSrxMnO3 and LaMnO3 manganites were measured. The effects of Sr contents on the microdefects of La1-xSrxMnO3 were investigated by means of positron lifetime results. The signals of 3d electrons of La1-xSrxMnO3 were extracted from the coincidence Doppler broadening spectra. The results show that the electron density of La1-xSrxMnO3 is larger than that of LaMnO3. The open volume of the defect in La1-xSrxMnO3 increases with the Sr contents. The signals of 3d electrons of ferromagnetic La1-xSrxMnO3 is larger than that of antiferromagnetic LaMnO3, and it reaches the maximum at x=0.33, that is, the signals of 3d electrons of the La0.67Sr0.33MnO3 is the highest in all testing samples, which corresponds to a lowest resistivity and a higher Curie temperature of the manganite. The influence of 3d electrons on the ferromagnetic double-exchange coupling and anti-ferromagnetic coupling of La1-xSrxMnO3 were discussed.

The 3d Electrons and Microdefects in Binary Ti-Al Alloys Studied by Positron Annihilation

2011 ◽  
Vol 399-401 ◽  
pp. 99-102
Author(s):  
Wen Deng ◽  
Xiao Lei Guo ◽  
Bing Xie ◽  
Ding Kang Xiong ◽  
Yu Yang Huang
Keyword(s):  
Grain Boundary ◽  
Positron Annihilation ◽  
Free Electron ◽  
Positron Lifetime ◽  
Al Alloys ◽  
Doppler Broadening ◽  
Al Content ◽  
Open Volume ◽  
Ti Content ◽  
Coincidence Doppler Broadening

The behavior of 3d electrons and microdefects in binary Ti-Al alloys with Al contents from 47at.% to 53at.% have been studied by coincidence Doppler broadening and positron lifetime techniques. It has been found that the 3d electron signals in the spectra of binary Ti-Al alloys increase with Ti content. In Al-rich Ti-Al alloys, on increasing Al content, the open volume of defect on grain boundary increases while the density of free electron decreases. On the contrary, in Ti-rich Ti-Al alloys, on increasing Ti content, the open volume of defect on grain boundary decreases, and the electron density of the grain boundary increases.

Defect Characterization in Thermoelectric Zn-Sb Systems by Positron Annihilation

2017 ◽  
Vol 373 ◽  
pp. 245-248
Author(s):  
Ting Zhang ◽  
Kai Zhou ◽  
Zhi Quan Chen
Keyword(s):  
Positron Annihilation ◽  
Momentum Distribution ◽  
Defect Characterization ◽  
Doppler Broadening ◽  
Lifetime Measurements ◽  
Electron Positron ◽  
Momentum Distributions ◽  
Positron Lifetimes ◽  
Doppler Broadening Spectra ◽  
Coincidence Doppler Broadening

Positron lifetimes and momentum distributions of annihilating electron-positron pairs have been calculated for vacancies in ZnSb and Zn4Sb3. The calculated positron lifetimes for bulk ZnSb and Zn4Sb3 are 203 ps and 208 ps, and for VZn in ZnSb and Zn4Sb3 are 249 ps and 237 ps respectively. The calculated momentum distribution results indicate the VZn in both ZnSb and Zn4Sb3 has less characterization from elemental Zn. Using coincidence Doppler broadening spectra combined with lifetime measurements can reveal the vacancy structure in ZnSb and Zn4Sb3.

Positron Lifetime Calculation for Plastic Deformed Nanocrystalline Copper

2017 ◽  
Vol 373 ◽  
pp. 31-34
Author(s):  
Kai Zhou ◽  
Ting Zhang
Keyword(s):  
Positron Annihilation ◽  
Deformation Mechanism ◽  
Positron Lifetime ◽  
Experimental Information ◽  
Point Of View ◽  
Nanocrystalline Copper ◽  
Mean Grain Size ◽  
Positron Lifetimes ◽  
Boundary Deformation

Positron lifetime calculation has been performed on a computer-generated nanocrystalline copper with a mean grain size of 9.1 nm during its deformation. For the undeformed and deformed nanocrystalline copper, calculated positron lifetimes are around 157 ps which come from the positron annihilation in the free volume in grain boundaries. Due to the grain-boundary deformation mechanism, no vacancies or vacancy clusters will be induced in grains during the plastic deformation of the nanocrystalline copper, which is different to the deformation of the conventional polycrystal. From this point of view, in-situ positron annihilation measurements can provide important experimental information on the deformation mechanism of nanocrystalline metals.

Positron annihilation lifetime and coincidence Doppler broadening study of γ-irradiated polyethylene

2005 ◽  
Vol 313 (1-3) ◽  
pp. 63-69 ◽  
Author(s):  
R.S. Yu ◽  
T. Suzuki ◽  
N. Djourelov ◽  
K. Kondo ◽  
Yasuo Ito ◽  
...  
Keyword(s):  
Positron Annihilation ◽  
Doppler Broadening ◽  
Positron Annihilation Lifetime ◽  
Coincidence Doppler Broadening

Effect of Fe2O3 Dopant on Electronic Densities and Electrical Properties of ZnO-Based Varistors

2011 ◽  
Vol 415-417 ◽  
pp. 1042-1045
Author(s):  
Wen Deng ◽  
Zhen Quan Lei ◽  
Jiao Ling Zhao ◽  
Yan Qiong Lu ◽  
Ding Kang Xiong
Keyword(s):  
Electrical Properties ◽  
Positron Lifetime ◽  
Nonlinear Coefficient ◽  
Doppler Broadening ◽  
Donor Concentration ◽  
Current Voltage ◽  
Electronic Densities ◽  
Current Voltage Characteristics ◽  
Doppler Broadening Spectra ◽  
Coincidence Doppler Broadening

The effect of the Fe2O3dopant on the electronic densities and the electrical properties has been studied in a ZnO-Bi2O3-SnO2-Co2O3-MnO2-TiO2-Ni2O3-Fe2O3system by the measurements of positron lifetime spectra, coincidence Doppler broadening spectra and current-voltage characteristics. The results show that the 3d electron signal in the spectrum of the varistor increases with the Fe2O3content. The addition of small amount of Fe2O3into the ZnO-based varistor leads to an increase in the donor concentration in the bulk and the defects in the varistor. As the Fe2O3content increased, the threshold voltage (VT) and the nonlinear coefficient (α) of the varistor decreased monotonously.

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