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A meta-analysis of published data in combination with measurements on Al, Cu, CuO, CrCoFeMnNi, Ni90Cr10, TiN, and V sputter deposited thin films, permits to demonstrate that the grain size-thickness correlation can be described by a power law. The exponent depends on the homologous temperature which is defined as the ratio between the deposition and the melting temperature of the studied material [1]. The exponent is close to 0.4 at a homologous temperature between approximately 0.15 and 0.3. Theoretical film growth models that depict an evolutionary overgrowth mechanism obtain the same exponent. Above a homologous temperature of approximately 0.3, a slightly higher exponent is observed which agrees with the general idea that at higher homologous temperatures the grain size is also influenced by restructuring mechanisms occurring during film growth. The exponent becomes substantially lower at low homologous temperatures (<0.15) [2]. From a theoretical point of view its value should be close to zero. The aforementioned boundaries of the homologous temperatures correspond with those observed in published structure zone models which describe the microstructure of physical vapor deposited thin films. The good agreement suggests that the underlying reason for the observed boundaries is the atom mobility. This hypothesis was further investigated by a study on the influence of intentionally added impurities on the power law behavior for Al and Cu thin films. A decrease of the grain size is observed for both materials when the impurity-to-metal flux ratio is increased. No change of the exponent is observed for Al, while for Cu the exponent becomes equal to zero at sufficiently high impurity-to-metal flux ratios. References [1] W. Giurlani, E. Berretti, M. Innocenti, and A. Lavacchi, Materials Proceedings 2 (2020), no. 1. [2] A. Dulmaa, F. G. Cougnon, R. Dedoncker, and D. Depla, Acta Materialia, 212 (2021) 116896
Sputter deposition of high reactivity metals such as calcium require some special preconditions, and hence less literature data is available on the influence of the deposition on the film growth. Nevertheless, calcium is an important alkali-earth element in many compounds such as mechanoluminescent materials [1], calcium batteries [2], but it has also received considerable attention in metallic form in for example polymer light-emitting diodes (LEDs) as the electron injection contact due to its low work-function [3]. In this work, calcium thin films were successfully synthesized by pulsed DC magnetron sputtering at room temperature. Due to its high reactivity with air, the calcium target was mounted on a magnetron using a glove box under a slight positive pressure of argon. To protect the calcium film from ambient air, a thin copper layer was deposited on both sides of the calcium film. X-ray diffraction (XRD), Fourier transform infrared (FTIR), and Scanning electron microscope (SEM) were used to confirm the crystal phase. We also studied the chemical stability of the calcium thin film. Long term exposure of the film to ambient conditions were performed. As for future work also CaO can be of importance the reactive sputtering behaviour of Ca was studied in detail.
CuO and Al thin films were successively deposited using direct current (reactive) magnetron sputter deposition. A multilayer of five bilayers was deposited on glass, which can be ignited by heating a Ti resistive thin film. The velocity of the reaction front which propagates along the multilayer was optically determined using a high-speed camera. During the deposition of the aluminum layers, air was intentionally leaked into the vacuum chamber to introduce impurities in the film. Depositions at different impurity/metal flux ratios were performed. The front velocity reaches a value of approximately 20 m/s at low flux ratios but drops to approximately 7 m/s at flux ratios between 0.6 and 1. The drop is rather abrupt as the front velocity stays constant above flux ratios larger than 1. This behavior is explained based on the hindrance of the oxygen transport from the oxidizer (CuO) to the fuel (Al).
Cementite-type carbides are of interest for magnetocaloric applications owing to their temperature- or pressure-induced magnetic phase transition. Here, using first-principles calculations, we investigate the magnetism and the magnetic phase transition in iron carbide (Fe3C) with the substitution of Cr atoms at Fe sites with the strain effect. The presence of Cr atoms is found to give rise to a second-order magnetic phase transition from a ferromagnetic phase for Fe3C to a nonmagnetic phase in chromium carbide (Cr3C).While the ternary Fe2CrC and Cr2FeC compounds prefer the ferrimagnetic ground state, the magnitudes of both the Fe and Cr spin moments, which are antiparallel in orientation, decrease as x increases in Fe3−xCrxC (x = 0, 1, 2, and 3). Furthermore, the fixed spin-moment calculations indicate that the magnetization of Fe3−xCrxC compounds can be delicately altered via the strain effect and that the magnetic-nonmagnetic phase transition occurs at an early stage of Cr substitution, x = 2.
Abstract The number of charge-discharge cycles in the lithium- iron- phosphate battery is limited by cathode degradation due to phase separation LiFePO4 → FePO4 + LiFePO4 .Same nature separation occurs spontaneously under ambient conditions in an optically transparent solid solution Na1-xAgxBr through formula Na1-xAgxBr → NaBr + AgBr. The mechanism of phase separation in Na1-xAgxBr can be used as a possible model of degradation of LiFePO4 cathode. In this paper, to study the phase separation in Na1-xAgxBr, a thin films of solid solutions at x = 0, 0.25, 0.50, 0.75, 1.0, were fabricated by rapid vacuum deposition (1-5 nm / s) of powder mixture on a glass or quartz substrates. Were also fabricated sandwiched films of the same thickness (100 nm), NaBr (t1) + AgBr (t2) where the thicknesses of layers t1 (t2) varied as 0 (100); 20 (80); 40 (60); 60 (40); 80 (20); 100 (0) nm. The absorption spectra of the films in a broad optical range of 200-900 nm, including the area of transparency of both layers and the absorption band of edge exciton of AgBr were measured with a daily interval. Morphological changes (granulation) in films were photographed through an optical microscope with 1000-fold magnification. The growth of the granules in a film were accompanied by transparency loss due to light scattering at the grains and widening of edge excitonic absorption band of AgBr. Annealing the films at 2000C before and after granulation slowed a growth of the granules, but did not lead to their disappearing. The work offers possible mechanism of granulation process in these films. Keywords: Thin films of a solid solution of Na1-xAgxBr, growth of granules, light scattering on a granules, excitonic absorption. Литература 1. Н.Тувжаргал, Б. Бат-Отгон, Ж. Даваасамбуу, Г. Еколд “ Изучение магнитных свойств и кинетики фазового разделения в LiхFePo4” Ученые записки Монгольского национального университета, серия “Физика” № 362 (17), стр. 108-110 (2012) 2. De Li, Haoshen Zhau “Two-phase transition of Li-intercalation compounds in Li-ion batteries” Materials Today, Volume 17, Issue 9, pages 451-463, November 2014. 3. This work has been done with financial support of the advanced research project of National University 4. of Mongolia on title: “Study of static displacement and phase transitions in solid solutions” (2016), 5. And the research project: “The investigation of heavy metal contamination of soil on Hanbogd and 6. Tsogttsetsii villages of Umnugobi province, where located OyuTolgoi and TavanTolgoi mines” (2015) 7. supported by the Asia Research Center, Mongolia and Korea Foundation for Advanced Studies, Korea. Acknowledgement This work has been done with financial support of the advanced research project of National University of Mongolia on title: “Study of static displacement and phase transitions in solid solutions” (2016), and the research project: “The investigation of heavy metal contamination of soil on Hanbogd and Tsogttsetsii villages of Umnugobi province, where located Oyu Tolgoi and Tavan Tolgoi mines” (2015) supported by the Asia Research Center, Mongolia and Korea Foundation for Advanced Studies, Korea.
Abstract The number of charge-discharge cycles in the lithium- iron- phosphate battery is limited by cathode degradation due to phase separation LiFePO4 → FePO4 + LiFePO4 .Same nature separation occurs spontaneously under ambient conditions in an optically transparent solid solution Na1-xAgxBr through formula Na1-xAgxBr → NaBr + AgBr. The mechanism of phase separation in Na1-xAgxBr can be used as a possible model of degradation of LiFePO4 cathode. In this paper, to study the phase separation in Na1-xAgxBr, a thin films of solid solutions at x = 0, 0.25, 0.50, 0.75, 1.0, were fabricated by rapid vacuum deposition (1-5 nm / s) of powder mixture on a glass or quartz substrates. Were also fabricated sandwiched films of the same thickness (100 nm), NaBr (t1) + AgBr (t2) where the thicknesses of layers t1 (t2) varied as 0 (100); 20 (80); 40 (60); 60 (40); 80 (20); 100 (0) nm. The absorption spectra of the films in a broad optical range of 200-900 nm, including the area of transparency of both layers and the absorption band of edge exciton of AgBr were measured with a daily interval. Morphological changes (granulation) in films were photographed through an optical microscope with 1000-fold magnification. The growth of the granules in a film were accompanied by transparency loss due to light scattering at the grains and widening of edge excitonic absorption band of AgBr. Annealing the films at 2000C before and after granulation slowed a growth of the granules, but did not lead to their disappearing. The work offers possible mechanism of granulation process in these films. Keywords: Thin films of a solid solution of Na1-xAgxBr, growth of granules, light scattering on a granules, excitonic absorption. Литература 1. Н.Тувжаргал, Б. Бат-Отгон, Ж. Даваасамбуу, Г. Еколд “ Изучение магнитных свойств и кинетики фазового разделения в LiхFePo4” Ученые записки Монгольского национального университета, серия “Физика” № 362 (17), стр. 108-110 (2012) 2. De Li, Haoshen Zhau “Two-phase transition of Li-intercalation compounds in Li-ion batteries” Materials Today, Volume 17, Issue 9, pages 451-463, November 2014. 3. This work has been done with financial support of the advanced research project of National University 4. of Mongolia on title: “Study of static displacement and phase transitions in solid solutions” (2016), 5. And the research project: “The investigation of heavy metal contamination of soil on Hanbogd and 6. Tsogttsetsii villages of Umnugobi province, where located OyuTolgoi and TavanTolgoi mines” (2015) 7. supported by the Asia Research Center, Mongolia and Korea Foundation for Advanced Studies, Korea. Acknowledgement This work has been done with financial support of the advanced research project of National University of Mongolia on title: “Study of static displacement and phase transitions in solid solutions” (2016), and the research project: “The investigation of heavy metal contamination of soil on Hanbogd and Tsogttsetsii villages of Umnugobi province, where located Oyu Tolgoi and Tavan Tolgoi mines” (2015) supported by the Asia Research Center, Mongolia and Korea Foundation for Advanced Studies, Korea.
Abstract Average copper recovery at the Erdenet Mining Corporation (EMC) is 86.5% and stable without any significant seasonal changes, while molybdenum recovery is lower (46%) and changes drastically during spring-summer season of each year. This molybdenum recovery volatility is the subject of this study. We suggest the bad and random molybdenum recovery is caused by seasonal changes of composition of dissolved salts, oxygen in circulating water that used for flotation enrichment at the EMC. The Central Research Laboratory (CRL) of the EML measures once at every month content of elements Cu, Fe, Ca, Mg, Mo and salt forming ions SO4 2- , HCO3 1- , CO3 2- and pH, hardness, dry residue in the circulating water. As shows our correlation analyses of CRL monthly data with weather data such as monthly average air temperature and moisture, wind speed, and precipitation during 2008-2011 years, content of dominant ions Ca2+, Mg2+ , SO4 2- , HCO3 1- and other ions in the circulating water changes seasonally: in summer-autumn season (July-to-October) content of dominant ions and dissolved oxygen, carbon dioxide changes rapidly in consistent with rainfall net amount and wind intensity; during winter time (November – to - March), when the artificial lake is mostly covered with ice, content of two dominant ions pair Ca2+ - SO4 2- is high and stable, simultaneously, content of dissolved oxygen falls 3-4 times to 2-3 ppm level. During March-April period, artificial lake ice cover melts and dilutes circulating water, decreasing the dry residue of the circulating water up to 15-20%. The end of May-to- end of June period is very special. During this relatively warm, dry, and windy time, the surface water of the artificial lake intensively evaporates and circulating water becomes thick as during winter peak time. At the same time, because of high intense dry winds, artificial lake enriches with dissolved oxygen and carbon dioxide gases. So the circulating water contains higher amount of dissolved oxygen and SO4 2- ions during the spring-to-summer period. Surface of molybdenite particles in the pulp media can be oxidized in two steps if a presence of dissolved oxygen and SO4 2- ions are simultaneous and sufficient. This two step surface oxidation increases hydrophilic property of the molybdenite particles in the pulp and consequently decreases their floatability and finally causes bad recovery of molybdenum at the EMC during the spring-to-summer period. Acknowledgement: This work has been done with financial support of the advanced research project of National University of Mongolia on title “Study of static displacement and phase transitions in solid solutions” (2016) and the research project: “The investigation of heavy metal contamination of soil on Hanbogd and Tsogttsetsii villages of Umnugobi province, where located Oyu Tolgoi and Tavan Tolgoi mines” (2015) supported by the Asia Research Center, Mongolia and Korea Foundation for Advanced Studies, Korea.
Molybdenum recovery efficiency seasonal instability at the Erdenet Mining Corporation Average copper recovery at the Erdenet Mining Corporation (EMC) is 86.5% and stable without any significant seasonal changes, while molybdenum recovery is lower (46%) and changes drastically during spring-summer season of each year. This molybdenum recovery volatility is the subject of this study. We suggest the bad and random molybdenum recovery is caused by seasonal changes of composition of dissolved salts, oxygen in circulating water that used for flotation enrichment at the EMC. The Central Research Laboratory (CRL) of the EML measures once at every month content of elements Cu, Fe, Ca, Mg, Mo and salt forming ions SO4 2-, HCO31-, CO32- and pH, hardness, dry residue in the circulating water. As shows our correlation analyses of CRL monthly data with weather data such as monthly average air temperature and moisture, wind speed, and precipitation during 2008-2011 years, content of dominant ions Ca2+, Mg2+ , SO4 2-, HCO31- and other ions in the circulating water changes seasonally: in summer-autumn season (July-to-October) content of dominant ions and dissolved oxygen, carbon dioxide changes rapidly in consistent with rainfall net amount and wind intensity; during winter time (November – to - March), when the artificial lake is mostly covered with ice, content of two dominant ions pair Ca2+ - SO4 2- is high and stable, simultaneously, content of dissolved oxygen falls 3-4 times to 2-3 ppm level. During March-April period, artificial lake ice cover melts and dilutes circulating water, decreasing the dry residue of the circulating water up to 15-20%. The end of May-to- end of June period is very special. During this relatively warm, dry, and windy time, the surface water of the artificial lake intensively evaporates and circulating water becomes thick as during winter peak time. At the same time, because of high intense dry winds, artificial lake enriches with dissolved oxygen and carbon dioxide gases. So the circulating water contains higher amount of dissolved oxygen and SO4 2- ions during the spring-to-summer period. Surface of molybdenite particles in the pulp media can be oxidized in two steps if a presence of dissolved oxygen and SO4 2- ions are simultaneous and sufficient. This two step surface oxidation increases hydrophilic property of the molybdenite particles in the pulp and consequently decreases their floatability and finally causes bad recovery of molybdenum at the EMC during the spring-to-summer period. Acknowledgement: This work has been done with financial support of the advanced research project of National University of Mongolia on title “Study of static displacement and phase transitions in solid solutions” (2016) and the research project: “The investigation of heavy metal contamination of soil on Hanbogd and Tsogttsetsii villages of Umnugobi province, where located Oyu Tolgoi and Tavan Tolgoi mines” (2015) supported by the Asia Research Center, Mongolia and Korea Foundation for Advanced Studies, Korea.
In calculations of the crystal lattice dynamics and elastic constants is still popular equations of G.L.Squires1, which are expressed through the Born-von-Karman force constants. The equations of G.L.Squires are successfully used by W.M.Shyu and G.D.Gaspari2 for calculations of elastic constants of simple FCC and BCC metals within pseudopotential theory, but it was revealed that the theoretical values of Born-von-Karman force constants significantly differ from experimental values calculated from the fitting of experimental phonon spectra. The Born-von-Karman force constants are not so convenient to use in fitting procedures of phonon spectra, because it is necessary up to six types of force constants on depending on the atomic coordinates. The temperature dependent elastic constants are usually dominated by anharrmonic interactions and the full theoretical treatment is rather involved.3 Our calculations are based on the plane wave self-consistent field (PWscf) method using the generalized gradient approximation (GGA) by Perdew and Wang (PW91)4 within the framework of density functional theory (DFT),5-6 as implemented in the QUANTUM ESPRESSO package.7 The following electronic state is treated as valence: Fe(3s23p63d64s1) and Cr(3s23p63d54s1) for atoms. The interaction between the ions and valence electrons is expressed as the ultrasoft pseudopotential.8 The wave functions are expressed as plane waves up to a kinetic energy cutoff of 40 Ry. The summation of charge densities is done using the special k-points generated by the 14x14x14 Monkhorst-Pack meshes.9 We used the tetrahedral method10 when we evaluate the electronic density of state (DOS). For the self-consistent cycle the total energy convergence is 10-5 eV. The occupation numbers of electrons are expressed Gaussian distribution function with an electronic temperature of kT = 0.001 Ry. The atomic ionic positions are relaxed at the fixed lattice parameters until the residual forces are less than 0.05 eV/Å. In this presentation, we will present the results of the magnetic phase stability, and predictions of lattice parameter and temperature dependent elastic constants of pure bcc Fe (FM), mixed bcc Fe0.5Cr0.5 (FM) and pure bcc Cr (AFM) using the quantum mechanical simple method by Fuchs11 and semiemperical Varshni expression.12 We will also compare the current results with the previous methods.13-14
