Johannes Kiefer

Perovskite materials are considered highly promising because their unique crystal structure enables exceptional properties for a variety of applications. Therefore, they have been a very active area of research for decades. Barium titanate (BaTiO₃), one of the most popular among these structures, has prompted various attempts to obtain this material, both on a micro- and nanoscale, due to its versatility in multiple disciplines and fields of technology. This article aims at providing an overview of the literature discussing synthesis and characterization of barium titanate materials. A detailed comparison shows the links between synthesis method and material properties. Moreover, we have condensed the literature into tables highlighting the main conclusions and allowing newcomers in the field to obtain a rather comprehensive picture of methods and approaches.

Attenuated total reflection (ATR) spectroscopy in infrared is a standard tool used in most analytical labs, as it allows a rapid chemical analysis with virtually no sample preparation. However, when the sample contains materials with a high refractive index, special care must be taken as the resulting data may be severely biased. This article reports a theoretical approach to correcting distorted ATR spectra. Starting from Snell's law, Lorenz model and Fresnel's equations are combined to obtain the complex relationship between optical constants. With calculating the real and imaginary parts, that is, n ( ν ) and k ( ν ) , respectively, of the complex refractive index from the absorption spectrum, a model for mixtures comprising of a liquid and a solid is established. The effects of distortion and potential misinterpretation of the data are discussed. Proof-of-concept experiments with mixtures of carbonaceous materials and toluene confirm the theoretically predicted observations.

The innovative development of reactive‐spray systems for gas‐phase production of metal sulfides are potential materials for next‐generation technologies. These flame‐synthesized sulfides (doped, functionalized, and heterogeneously mixed derivatives) hold significant potential as photocatalysts for water splitting. The knowledge acquired from nonaqueous precursor‐solvent and high‐temperature aerosol chemistries, optimal process parameters are established to generate In_2‐(4/3)xSn_xS₃, solid‐solutions. The thermally driven reducing gas‐phase reactions are controlled through fuel/oxygen ratio. Particles characterizations (X‐ray diffraction, transmission electron microscopy (TEM) and imaging) revealed structural stability and crystallinity. The In_2‐(4/3)xSn_xS₃, at higher Sn doping had enhanced photoexcitation. Donor‐acceptor levels within the material facilitated electron‐hole pair trapping, crucial for redox reactions. With suitable band gap energies for water oxidation (1.9‐1.1 eV) closely matched flat band potentials (4.38‐4.67 eV) for redox reactions. The powder characterization showed 8% In₂O₃ in InSn_0.75S₃ after photocatalysis due to S‐degradation in the initial light “on/off cycles”. The pioneering process of employing oxygen‐deficient reducing flame enabled a series of photo‐catalytically active metal sulfide nanoparticles with work function energies in the range of 5.19‐5.37 eV. This synthesis strategy holds the potential for impactful advancements in both industry and R&D, addressing the urgent need for new materials capable of inducing water oxidation under visible light.

Raman spectroscopy and laser-induced breakdown spectroscopy (LIBS) are powerful tools for molecular and elemental analysis, respectively. Their combined application, however, is challenging due to the differences in the signal generation and detection characteristics. This note proposes three experimental schemes for the simultaneous application of Raman and LIBS for gas-phase diagnostics. Ring-cavity optical pulse stretchers facilitate shaping suitable pulse pairs from a Q-switched laser that enables the quasi-simultaneous detection of the Raman and LIBS signals on a single detector.

Laser-induced breakdown spectroscopy (LIBS), accompanied by chemometric data analysis, is used to identify and classify gemstones of various hardness. The study involves several gemstones: amethyst, aquamarine beryl, bloodstone citrine, diopside, and enstatite. Their hardness is determined through a correlation utilizing the spectral intensity ratio of the ionic to atomic spectral lines of an identified element in the LIB spectrum. The result of the relative hardness obtained from the LIBS analysis is in good agreement with the hardness measured from Mohs’s scale of hardness, a popular qualitative method to determine hardness. In this work, a linear relationship has been established between the Mohs’s hardness and the plasma excitation temperature. Thus, the hardness of the gemstones can be determined with the help of plasma excitation temperature. Moreover, the analysis of trace elements in LIB spectral data reveals that a particular element is responsible for the colors of gemstones. Therefore, the relative concentration of constituents is calculated for all gemstones and compared. Principal component analysis (PCA) is successfully applied to all gemstone spectra for rapid classification and discrimination based on their variable elemental concentrations and respective hardness.

Thermometry utilizing the vibrational spectrum of nitrogen is a very common tool in combustion diagnostics via spontaneous and coherent Raman scattering spectroscopy. In the presence of strong temperature gradients, however, it is likely that hot and cold gas portions contribute to the signal. This is known as spatial averaging, and it can result in severe measurement errors. The present work proposes and demonstrates two straightforward approaches that allow the identification of spatial averaging as well as estimating the resulting error. For this purpose, simulated Raman spectra are considered in order to avoid any impact from experimental artifacts. The first approach utilizes difference spectra, whereas the second one is based upon principal component analysis (PCA). Two scenarios were tested: (1) spectra of 50:50 mixtures exhibiting a common mean temperature and (2) spectra of mixtures with systematically varied fractions of hot (2000 K) and cold (300 K) gas. It is shown that the resulting measurement error can be as high as 500 K.