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- Chesnokov, A., et al.
(författare)
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The local atomic structure and thermoelectric properties of Ir-doped ZnO : hybrid DFT calculations and XAS experiments
- 2021
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Ingår i: Journal of Materials Chemistry C. - : Royal Society of Chemistry. - 2050-7526 .- 2050-7534. ; 9:14, s. 4948-4960
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Tidskriftsartikel (refereegranskat)abstract
- We combined the hybrid density functional theory (DFT) calculations and X-ray absorption spectroscopy (XAS) experiments in the study of the local atomic structure around Ir ions in ZnO thin films with different iridium content. This was then used in the first principles analysis of the thermoelectric properties of material. The emphasis has been put on the conditions for a positive Seebeck coefficient and p-type electrical conductivity as the functions of the Fermi level. We studied both computationally and experimentally several possible IrOxpolyhedra (complexes) with a different number of surrounding oxygens and Ir oxidation states, including those with the formation of peroxide ions (O22−). In particular, octahedral coordination of iridium ions was identified by reverse Monte Carlo (RMC) simulations of the Ir L3-edge EXAFS spectra of ZnO:Ir thin films as the predominant complex, which is supported by the calculated lowest interstitial oxygen incorporation energies. All the calculated IrOx(x= 4, 5, 6) complexes, regardless of Ir the oxidation state, demonstrate potential for p-type conduction if the Fermi level (μF) falls in the range of 0-0.8 eV from the valence band maximum (VBM) and the Ir concentration is high enough (12.5% in the present DFT calculations). Even though the corresponding calculated Seebeck coefficient (S) around 80-89 μV K−1slightly exceeds the experimental values, we emphasise the presence of an important plateau in the dependence ofSonμFin this range for two complexes with the formation of peroxide ions (O22−). We predicted also that peroxide ions O22−are characterized by the calculated phonon frequencies of 810-942 cm−1in agreement with our previous Raman experimental results. In this light, we discuss the high sensitivity of calculatedS(μF) dependences to the atomic and electronic structure.
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| 2. |
- Chipiga, Larisa, et al.
(författare)
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Assessment of patient doses and corresponding radiation risks from PET/CT examinations in the Russian Federation
- 2019
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Ingår i: 5th International Conference on X-Ray, Electrovacuum and Biomedical Technique. - : Author(s). - 9780735418196 ; 2089
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Konferensbidrag (refereegranskat)abstract
- In the current study we evaluated the structure of positron emission tomography combined with computed tomography (PET/CT) diagnostics in the Russian Federation. Patient effective doses, organ doses and corresponding radiation risks for the most common PET/CT examinations were evaluated. Data was collected in 12 regions of the Russian Federation in the period 2012-2017 in 19 facilities (26 PET/CT scanners, corresponding to more than 60 % of the scanners in the country). Typical administered activities and DLP values for the CT protocols were estimated with the subsequent calculation of typical organ and effective doses from external and internal exposure. Lifetime radiation detriment-adjusted risks were calculated based on both the effective dose and organ absorbed doses considering the gender of the patient. The results of the dose survey indicate that the most common PET/CT examinations are whole body and brain examinations with 18F-FDG (performed in 26 and 8 surveyed departments respectively). Other PET/CT examinations are significantly less common. The highest patient doses were calculated for whole body PET/CT examinations - about 20 mSv. The doses increase up to 35-40 mSv if multiphase CT scan was performed, the CT scan composed up to 70-90 % of the total effective dose. Lifetime detriment-adjusted risk was estimated for PET/CT examinations of the brain as 2·10 -4 ; for pelvic as 5·10 -4 , and may reach up to 10 -3 for whole body PET/CT examinations. Comparison of risks assessed by two approaches indicated that the simplified risk assessment based on effective dose overestimated the risk for PET/CT examinations of the brain (both genders) and for whole body and pelvic examinations (males only). Overall, differences in male and female patients can reach up to the 30 %.
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