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Acceptor-substituted Ba(Zr,Ce)O3 proton conducting oxides have attracted significant attention due to their excellent proton conductivity at intermediate temperatures (400–600 °C). A high Zr/Ce ratio is crucial for maintaining stability in humid or other harsh atmospheres. Herein, a systematic study was conducted on the phase composition, microstructure, and the resulting hydration ability and electrochemical performance of high Zr/Ce ratio Ba(Zr,Ce)O3 solid solutions with different Y substitution levels (10 at% to 30 at%). In this substitution range, no apparent secondary phase can be found from XRD, leading to a continuous increase in hydration content. A Y-rich phase was observed in SEM for compositions with high levels of Y substitution. The impact of Y on proton conduction was examined using EIS, with particular attention on elucidating the effects of varying amounts of Y on bulk proton conduction. The increase of proton conductivity was primarily due to the increased charge carrier (proton) concentration caused by Y substitution. Different concentrations of Y have little effect on proton mobility, indicating a compromise between different mechanisms such as the Y trapping effect and the nano-percolation effect. Grain boundary proton conduction was discussed combining the TEM-EDS results to explain the space charge layer effect. Mechanical properties and thermo-chemical stability were also considered to pave the way for real applications. [ABSTRACT FROM AUTHOR]

Acceptor‐doped barium zirconates are of major interest as proton‐conducting ceramics for electrochemical applications at intermediate operating temperatures. However, the proton transport through polycrystalline microstructures is hindered by the presence of a positive space charge potential at grain boundaries. During high‐temperature sintering, the positive charge acts as a driving force for acceptor dopant segregation to the grain boundary. Acceptor segregation to grain boundaries has been observed in sintered ceramics, but the fundamental relationship between the segregation kinetics and the protonic conductivity is poorly understood. Here, a comprehensive study of the influence of acceptor dopant segregation on the electrochemical properties of grain boundaries in barium zirconate ceramics is presented. An out‐of‐equilibrium model material that displays no detectable Y segregation at its grain boundaries is explicitly designed. This model material serves as a starting point to measure the kinetics of segregation and the induced changes in grain boundary conductivity upon varying thermal histories. Furthermore, the electrochemical results from impedance spectroscopy to atomic resolution transmission electron microscopy, atom probe tomography, and DFT simulations are correlated. It is discovered that acceptor dopant segregation drastically increases the proton conductivity in both the model system and several other application‐relevant compositions. [ABSTRACT FROM AUTHOR]

Plasma etching is a crucial step in semiconductor manufacturing. High cleanliness and wafer‐to‐wafer reproducibility in the etching chamber are essential in order to successfully achieve nanometer‐sized integrated functions on the wafer. The trend toward the application of more aggressive plasma compositions leads to higher demands on the plasma resistance of the materials used in the etching chamber. Due to its excellent etch resistance, yttrium aluminum garnet Y3Al5O12 (YAG) is starting to replace established materials like SiO2 or Al2O3 in this kind of application. In this study, reactive spark plasma sintering (SPS) was used to manufacture highly dense YAG ceramics from the respective oxides. In addition, yttrium was replaced with heavier lanthanoids (Er, Lu), intending to investigate the role of the A‐site cation in the garnet type structure on the plasma erosion behavior. The produced materials were exposed to fluorine‐based etching plasmas mimicking the conditions in the semiconductor manufacturing apparatus and the erosion behavior was characterized by atomic force microscopy (AFM), secondary ion mass spectrometry (SIMS), transmission electron microscopy (TEM), and profilometry. The induced chemical gradient in the samples is limited to a few nanometers below the surface, which makes its characterization challenging. For advanced analysis, we developed a correlative characterization method combining SIMS and scanning TEM (STEM)–energy‐dispersive spectroscopy (EDS) enabling us to examine the structural and chemical changes in the reaction layer locally resolved. In the case of lanthanoid aluminates, an altered reaction layer and reduced fluorine penetration compared to YAG were found. However, a correlation between the characteristics of the induced chemical gradient and the determined physical erosion rates was not evident. [ABSTRACT FROM AUTHOR]

Due to the increasing number of applications for ceramic components in reactive etching processes, the interest in the specific erosion behavior of highly etch‐resistant materials like yttrium oxide (Y2O3) has increased in the past years. Despite the large number of investigations already existing in this field, a more general understanding of the erosion mechanisms still lacks due to the limited comparability of these investigations. The huge difference in the kind of etching setups, processing parameters (bias voltage and plasma gas composition), and sample microstructures prevented consistent conclusions so far. To achieve a more general understanding, this study investigates the erosion behavior Y2O3 under a broad spectrum of plasma etching parameters. Therefore, the bias voltage is increased from 50 to 300 V and the plasma gas composition is gradually changed from Ar‐rich to CF4‐rich compositions. This systematic approach allows to directly correlate the morphology changes caused by plasma erosion with the related plasma etching parameters and enables to better understand their influence on the depth of physical and chemical interactions, surface damage, and etching rate. We discovered three distinct erosion regimes, which exhibit specific erosion characteristics. Using these observations, a schematic processing map for Y2O3 was developed, which could help to estimate the severity of the erosion attack dependent on the processing parameters. [ABSTRACT FROM AUTHOR]

Cation doping of Y2O3 is an established approach for tailoring densification and grain growth during sintering. However, the segregation of doped cations to the grain boundary and their impact on processing are still not completely understood. Segregation can be driven by electrostatic effects due to charge mismatch with the host lattice or elastic effects induced by ion size mismatch. While segregation is caused by thermodynamics, it impacts diffusion and the kinetics of grain boundaries during densification and microstructure evolution. In this study, we utilize two isovalent dopants (La3+ and Gd3+), that is we focus on the elastic component of segregation. We investigate the densification as well as the grain growth kinetics of both doped and undoped Y2O3 during field‐assisted sintering/spark plasma sintering (FAST/SPS). While Gd3+ is showing no significant effect on densification, La3+ resulted in a strongly reduced sintering activity. Furthermore, the analysis of the grain growth behavior during sintering and on predensified samples revealed a decrease in the grain growth coefficient, with La3+ having the strongest impact. The structure and chemistry at the grain boundary were observed by aberration‐corrected TEM. While no structural change was caused by doping, the chemical analysis showed a strong segregation of La3+ to the grain boundary, which could not be observed for Gd3+. The results indicate that segregated La3+ causes a drastic decrease in grain boundary migration rates through solute drag as well as much slower sintering kinetics, likely caused by a decrease in the grain boundary self‐diffusion due to segregation. This study further underlines the importance of the elastic contribution to cation segregation and establishes a clear relationship to grain growth and sintering kinetics, which are both decreased by segregation. [ABSTRACT FROM AUTHOR]

Cation doping of Y2O3 is an established approach for tailoring densification and grain growth during sintering. However, the segregation of doped cations to the grain boundary and their impact on processing are still not completely understood. Segregation can be driven by electrostatic effects due to charge mismatch with the host lattice or elastic effects induced by ion size mismatch. While segregation is caused by thermodynamics, it impacts diffusion and the kinetics of grain boundaries during densification and microstructure evolution. In this study, we utilize two isovalent dopants (La3+ and Gd3+), that is we focus on the elastic component of segregation. We investigate the densification as well as the grain growth kinetics of both doped and undoped Y2O3 during field‐assisted sintering/spark plasma sintering (FAST/SPS). While Gd3+ is showing no significant effect on densification, La3+ resulted in a strongly reduced sintering activity. Furthermore, the analysis of the grain growth behavior during sintering and on predensified samples revealed a decrease in the grain growth coefficient, with La3+ having the strongest impact. The structure and chemistry at the grain boundary were observed by aberration‐corrected TEM. While no structural change was caused by doping, the chemical analysis showed a strong segregation of La3+ to the grain boundary, which could not be observed for Gd3+. The results indicate that segregated La3+ causes a drastic decrease in grain boundary migration rates through solute drag as well as much slower sintering kinetics, likely caused by a decrease in the grain boundary self‐diffusion due to segregation. This study further underlines the importance of the elastic contribution to cation segregation and establishes a clear relationship to grain growth and sintering kinetics, which are both decreased by segregation. [ABSTRACT FROM AUTHOR]

Even though advanced ceramics are widely applied as consumables in semiconductor etching processes, the erosion mechanisms and connected surface phenomena are not fully understood. Through the interaction with reactive species and ion bombardment during the plasma exposure, oxide ceramic materials like Y2O3 are eroded by a physicochemical mechanism. In this study, fundamental phenomena of surface‐plasma interactions were investigated directly at the surface as well as in the near‐surface region after exposure to fluorine‐based etching plasmas. A straightforward re‐localization technique was used to investigate the microstructural features before and after the plasma exposure for up to 2 hours. Electron microscopy methods (scanning electron microscopy, electron backscatter diffraction) were coupled with atomic force microscopy, secondary ion mass spectroscopy, and transmission electron microscopy to study the surface topography and the corresponding reaction layer. Direct correlation of the microstructure before plasma exposure with the surface topography reveals a novel orientation‐dependent erosion mechanism that forms plateau‐like structures. Furthermore, the in‐depth analysis of the near‐surface area highlights the influence of the applied bias voltage on the physical damage and chemical gradient formation due to plasma exposure. The combined investigation of surface morphology and near‐surface properties reveals new fundamental aspects of the erosion behavior of polycrystalline yttria in CF4‐based etching plasmas. [ABSTRACT FROM AUTHOR]

Acceptor-substituted Ba(Zr,Ce)O 3 proton conducting oxides have attracted significant attention due to their excellent proton conductivity at intermediate temperatures (400-600 °C). A high Zr/Ce ratio is crucial for maintaining stability in humid or other harsh atmospheres. Herein, a systematic study was conducted on the phase composition, microstructure, and the resulting hydration ability and electrochemical performance of high Zr/Ce ratio Ba(Zr,Ce)O 3 solid solutions with different Y substitution levels (10 at% to 30 at%). In this substitution range, no apparent secondary phase can be found from XRD, leading to a continuous increase in hydration content. A Y-rich phase was observed in SEM for compositions with high levels of Y substitution. The impact of Y on proton conduction was examined using EIS, with particular attention on elucidating the effects of varying amounts of Y on bulk proton conduction. The increase of proton conductivity was primarily due to the increased charge carrier (proton) concentration caused by Y substitution. Different concentrations of Y have little effect on proton mobility, indicating a compromise between different mechanisms such as the Y trapping effect and the nano-percolation effect. Grain boundary proton conduction was discussed combining the TEM-EDS results to explain the space charge layer effect. Mechanical properties and thermo-chemical stability were also considered to pave the way for real applications.