scholarly journals Deconvolution of positron annihilation coincidence Doppler broadening spectra using an iterative projected Newton method with non-negativity constraints

2003 ◽  
Vol 74 (11) ◽  
pp. 4779-4787 ◽  
Author(s):  
K. F. Ho ◽  
C. D. Beling ◽  
S. Fung ◽  
Vincent K. W. Cheng ◽  
Michael K. Ng ◽  
...  
Keyword(s):  
Positron Annihilation ◽  
Newton Method ◽  
Doppler Broadening ◽  
Doppler Broadening Spectra ◽  
Projected Newton Method ◽  
Coincidence Doppler Broadening

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.

Influence of Nb and Sn on d Electrons of TiAl Alloys Studied by Coincidence Positron Annihilation Spectroscopy

2011 ◽  
Vol 415-417 ◽  
pp. 1132-1135
Author(s):  
Juan Gao ◽  
Jing Ying Ye ◽  
Wen Chun Zhang ◽  
Hui Juan Wang ◽  
Wen Deng
Keyword(s):  
Single Crystals ◽  
Positron Annihilation ◽  
Tial Alloy ◽  
Positron Annihilation Spectroscopy ◽  
Doppler Broadening ◽  
Tial Alloys ◽  
3D Electron ◽  
Doppler Broadening Spectra ◽  
Coincidence Doppler Broadening

The coincidence Doppler broadening spectra of single crystals of Si, Al, polycrystals of Ti, Nb and Sn, and TiAl-based alloys (TiAl, Ti50Al48Nb2and Ti50Al48Sn2) have been measured and analyzed. It has been found that the 3d electron signal for binary TiAl alloy is lower than expected due to the Ti 3d-Al 3p interactions. The addition of Nb atoms to TiAl alloy leads to the enhancement of d-d interactions and thus the d electron signal in the spectrum. The d electron signal in the spectrum of Ti50Al48Nb2alloy is higher than that of Ti50Al48Sn2alloy. The influence of Nb and Sn on d electrons of TiAl alloys has been discussed.

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 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

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.

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.

POSITRON INTERACTION IN POLYMERS

2004 ◽  
Vol 19 (23) ◽  
pp. 3951-3959 ◽  
Author(s):  
CORINE BAS ◽  
N. DOMINIQUE ALBÉROLA ◽  
MARIE-FRANCE BARTHE ◽  
JÉRÉMIE De BAERDEMAEKER ◽  
CHARLES DAUWE
Keyword(s):  
Positron Annihilation ◽  
Chemical Structure ◽  
Positron Beam ◽  
Positron Annihilation Spectroscopy ◽  
Hole Size ◽  
Doppler Broadening ◽  
Positron Source ◽  
Positron Annihilation Lifetime ◽  
Doppler Broadening Spectra ◽  
Variable Energy

A series of dense copolyimide membranes was characterized using positron annihilation spectroscopy. The positron annihilation lifetime spectroscopy performed on film with a classical positron source gives informations on the positronium fraction formed and also on the hole size within the film. The Doppler broadening spectra (DBS) of the gamma annihilation rays coupled with a variable energy positron beam allow the microstructural analyses as a function of the film depth. Experimental data were also linked to the chemical structure of the polyimides. It was found that the presence of the fluorine atoms strongly affects the positron annihilitation process and especially the DBS responses.

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