Surface thermodynamics of yttrium titanate pyrochlore nanomaterials.

Nanocrystalline pyrochlore materials have been investigated for their enhanced radiation tolerance as ceramic nuclear waste hosts. In this work, we study the thermodynamic driving force of nano-scale materials for radiation resistance. The size dependent thermodynamic properties of a series of Y2Ti2O7 nanoparticles were investigated. Samples were synthesized by a sol-gel method and characterized by synchrotron X-ray diffraction, BET analysis, and thermogravimetric analysis. The surface and interface enthalpies of Y2Ti2O7 were determined by high temperature oxide melt drop solution calorimetry to be 4.07 J m-2 and 3.04 J m-2, respectively. The experimentally obtained surface energy is in good agreement with computationally derived average surface energies for yttrium and other rare-earth titanate pyrochlores. Theoretical links between nanoparticle stability, surface energy, and radiation resistance of pyrochlore materials were then explored.

Energetic Stability and Interfacial Complexity of Ti3C2Tx MXenes Synthesized with HF/HCl and CoF2/HCl as Etching Agents.

MXenes are ultra-thin two-dimensional layered early transition-metal carbides and nitrides with potential applications in various emerging technologies, such as energy storage, water purification, and catalysis. MXenes are synthesized from the parent MAX phases with different etching agents [hydrofluoric acid (HF) or fluoride salts with a strong acid] by selectively removing a more weakly bound crystalline layer of Al or Ga replaced by surface groups (-O, -F, -OH, etc.). Ti3C2Tx MXene synthesized by CoF2/HCl etching has layered heterogeneity due to intercalated Al3+ and Co2+ that act as pillars for interlayer spacings. This study investigates the impacts of etching environments on the compositional, interfacial, structural, and thermodynamic properties of Ti3C2Tx MXenes. Specifically, compared with HF/HCl etching, CoF2/HCl treatment leads to a Ti3C2Tx MXene with a broader distribution of interlayer distances, increased number of intercalated cations, and decreased degree of hydration. Moreover, we determine the enthalpies of formation at 25 °C (ΔHf,25°C) of Ti3C2Tx MXenes etched with CoF2/HCl, ΔHf,25°C = -1891.7 ± 35.7 kJ/mol Ti3C2, and etched with HF/HCl, ΔHf,25°C = -1978.2 ± 35.7 kJ/mol Ti3C2, using high-temperature oxidation drop calorimetry. These energetic data are discussed and compared with experimentally derived and computationally predicted values to elucidate the effects of intercalants and surface groups of MXenes. We find that MXenes with intercalated metal cations have a less exothermic ΔHf,25°C from an increase in the interlayer space and dimension heterogeneity and a decrease in the degree of hydration leading to reduced layer-layer van der Waals interactions and weakened hydration effects applied on the MXene layers. The outcomes of this study further our understanding of MXene's energetic-structural-interfacial property relationships.

Digital Mass Analysis in a Linear Ion Trap without Auxiliary Waveforms.

Mass analysis in a linear ion trap is traditionally performed using resonant ejection induced by auxiliary waveforms. For sinusoidally driven ion traps without resonant ejection, resolution and sensitivity are poor because mass-selected instability yields excitation along both the x and y axes simultaneously. Digital ion traps, on the other hand, have the advantage of duty cycle manipulation that can be used to change the ion excitation along the x and y axes. Consequently, the duty cycle can be used to enhance the resolution and sensitivity for mass-selected instability in a linear ion trap without the application of an auxiliary waveform. This work introduces and explores mass-selected instability in a linear trap without the use of auxiliary waveforms.