The formation mechanisms of the complex Ca-rich ferrite iron ore sinter bonding phases SFCA and SFCA-I, during heating of a synthetic sinter mixture in the range 298-1 623 K and at pO2 = 0.21, 5 × 10 -3 and 1 × 10 -4 atm, were determined using in situ X-ray diffraction. SFCA and, in particular, SFCA-I are desirable bonding phases in iron ore sinter, and improved understanding of the effect of parameters such as pO2 on their formation may lead to improved ability to maximise their formation in industrial sintering processes. SFCA-I and SFCA were both observed to form at pO2 = 0.21 and 5 × 10 -3 atm, with the formation of SFCA-I preceding SFCA formation in each case, but via distinctly different mechanisms at each pO2. No SFCA-I was observed at pO2 = 1 × 10 -4 atm; instead, a Ca-rich phase designated CFAlSi, formed at 1 420 K. By 1 456 K, CFAlSi had decomposed to form melt and a small amount of SFCA. Such a low pO2 during heating of industrial sinter mixtures is, therefore, undesirable, since it would not result in the formation of an abundance of SFCA and SFCA-I bonding phases. In addition, CFA phase, which was determined by Webster et al. (Metall. Mater. Trans. B, 43(2012), 1344) to be a key precursor phase in the formation of SFCA at pO2 = 5 × 10 -3 atm, was also observed to form at pO2 = 0.21 and 1 × 10 -4 atm, with the amount decreasing with increasing pO2.KEY WORDS: iron ore sinter; complex Ca-rich ferrite sinter bonding phases; SFCA and SFCA-I; in situ X-ray diffraction; oxygen partial pressure; phase formation mechanisms; synchrotron X-ray diffraction.
Herein we outline a general one-pot
method to produce large quantities
of compositionally tunable, kesterite Cu2ZnSnS4 (CZTS) nanocrystals (NCs) through the decomposition of in situ generated
metal sulfide precursors. This method uses air stable precursors and
should be applicable to the synthesis of a range of metal sulfides.
We examine the formation of the ligands, precursors, and particles
in turn. Direct reaction of CS2 with the aliphatic primary
amines and thiols that already constitute the reaction mixture is
used to produce ligands in situ. Through the use of 1H
and 13C nuclear magnetic resonance, Fourier transform infrared
spectroscopy, and optical absorption spectroscopy, we elucidate the
formation of the resulting oleyldithiocarbamate and dodecyltrithiocarbonate
ligands. The decomposition of their corresponding metal complexes
at temperatures of ∼100 °C yields nuclei with a size of
1–2 nm, with further growth facilitated by the decomposition
of dodecanethiol. In this way the nucleation and growth stages of
the reaction are decoupled, allowing for the generation of NCs at
high concentrations. Using in situ X-ray diffraction, we monitor the
evolution of our reactions, thus enabling a real-time glimpse into
the formation of Cu2ZnSnS4 NCs. For completeness,
the surface chemistry and the electronic structure of the resulting
CZTS NCs are studied.
The synthesis of an air and moisture stable germanium complex and its use in the synthesis of ternary and quaternary copper containing nanocrystals (NCs) is described. Through the use of 1 H-/ 13 C nuclear magnetic resonance and Fourier transform infrared spectroscopies, thermogravimetric analysis, and powder X-ray diffraction, the speciation and chemistry of this precursor is elucidated. This germanium source is employed in the gram scale, noninjection synthesis of Cu 2 ZnGeS 4 (CZGeS) and Cu 2 GeS 3 (CGeS) NCs using a binary sulfide precursor approach. To demonstrate the versatility of such NCs for fabricating thin films suitable for high-efficiency optoelectronic devices, they are blended with Cu 2 ZnSnS 4 (CZTS) NCs and selenized to form homogeneously alloyed Cu 2 ZnSn x Ge 1−x S y Se 4−y (CZTGeSSe) thin films. The structural, optical, and electronic properties of such thin films are studied using X-ray diffraction, scanning electron microscopy, UV−vis−NIR spectroscopy, and photoelectron spectroscopy in air. These measurements demonstrate collectively that incorporating Ge into micrometer-sized, tetragonal Cu 2 ZnSnS x Se 4−x (CZTSSe) provides a facile manner in which the conduction band energy can be readily tuned. The strategy developed herein provides a pathway to controlled levels of Ge incorporation in a single step process, thus avoiding the need for intra-alloyed Cu 2 ZnSn x Ge 1−x S 4 nanocrystals.
The formation mechanisms of the complex Ca-rich ferrite phase SFCA-I, an important bonding material in iron ore sinter, during heating of synthetic sinter mixtures in the temperature range 298-1 623 K in air and at pO2 = 5 × 10 -3 atm, were determined using in situ X-ray powder diffraction. In air, the initial formation of SFCA-I at ~1 438 K (depending on composition) was associated with reaction of precursor phases Fe2O3, CaO·Fe2O3, SiO2, amorphous Al-oxide and a CFA phase of approximate composition 71.7 mass% Fe2O3, 12.9 mass% CaO, 0.3 mass% SiO2 and 15.1 mass% Al2O3. At temperatures above ~1 453 K, the decomposition of another phase, γ -CFF, resulted in the formation of additional SFCA-I. At lower oxygen partial pressure the initial formation of SFCA-I occurred at similar temperatures and was associated with reaction between similar phases as its formation in air. However, the decomposition of γ -CFF did not result in the formation of additional SFCA-I, with the maximum SFCA-I concentration (25 mass%) lower than the values attained in air (54 and 34 mass%). Hence, more oxidising conditions appear to favour the formation of the desirable SFCA-I phase.KEY WORDS: iron ore sinter; SFCA and SFCA-I; in situ X-ray diffraction; Rietveld refinement-based quantitative phase analysis; SFCA-I formation mechanisms.
Raman spectroscopy is a powerful technique for the study of materials chemistry and nanostructure. This nondestructive technique is highly sensitive to molecular and crystal lattice vibrations, which allow for a comprehensive study of the vibrational modes of molecules incorporated in photovoltaic perovskite materials. In this study, we apply Raman spectroscopy to study FAPbX 3 (X = Cl, Br, I) and FA x MA 1−x PbI 3 (FA stands for formamidinium; MA for methylammonium) metal halide perovskite single crystals and discuss the necessary conditions to obtain reliable data. We establish a correlation between perovskite composition and their unique Raman intensities/spectral shapes. In particular, we show that tuning of the halide content results in a spectral shift of the organic features of the Raman spectrum due to changes in the strength of hydrogen bonding, while tuning of the organic cation is related more to changes in peak intensity. Moreover, the effect of temperature on the vibrational modes corresponding to NCN bending, NH 2 torsion, and NH 2 wagging were studied. This enables the impact of the organic composition in FA x MA 1−x PbI 3 on the phase transition temperature of the material to be determined. Furthermore, we establish links between Raman spectroscopy and other conventional measurement techniques such as X-ray diffraction (XRD) and differential scanning calorimetry (DSC). This study provides insight into the interpretation of the Raman spectra of FA-based perovskites, which furthers understanding of the properties of these materials in relation to their full exploitation in solar cells.
Throughout this text the acronym 'SFCA' in single quotation marks refers to undifferentiated 'SFCA'-like phases. These may consist of substituted calcium ferrites, SFCA sensu stricto and SFCA-I.
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