Rare earth elements (REEs), the 15 naturally occurring lanthanides plus yttrium and scandium, are ubiquitously used in modern life as they are critical components of many advanced devices and technologies. However, the demand for REEs is not equal, with the heavy rare earth elements (HREEs) having a higher demand. Xenotime (HREEPO4) is an important HREE ore mineral and globally is an economical source of HREE. Most of the crystallographic and thermodynamic properties of xenotime endmembers have been elucidated by calorimetric, solubility, and high-pressure studies. Yet, in natural systems, endmembers are rarely encountered, and instead, REE solid solutions are more commonly observed. In this work, we characterize the crystal chemistry, thermodynamics of HREE mixing, and high-temperature material behaviors and thermochemistry of a synthetic erbium (Er)–ytterbium (Yb) binary xenotime solid solution (Er(x)Yb(1–x)PO4) using a suite of experimental techniques, including X-ray fluorescence spectroscopy, synchrotron X-ray powder diffraction implemented with Rietveld analysis, Fourier transform infrared spectroscopy coupled with attenuated total reflectance, Raman spectroscopy, thermogravimetric analysis coupled with differential scanning calorimetry, and high-temperature oxide melt drop solution calorimetry. Our results shed light on the formation of natural xenotimes and lay the foundation for their industrial applications as thermal coating materials.

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 massselected instability in a linear trap without the use of auxiliary waveforms.

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.). Ti3C2T x 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 Ti3C2T x MXenes. Specifically, compared with HF/HCl etching, CoF2/HCl treatment leads to a Ti3C2T x 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 (ΔH f,25°C) of Ti3C2T x MXenes etched with CoF2/HCl, ΔH f,25°C = −1891.7 ± 35.7 kJ/mol Ti3C2, and etched with HF/HCl, ΔH f,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 ΔH f,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.

Once confined in zeolites, carbides of inexpensive transition metals, such as molybdenum (Mo) and tungsten (W), exhibit similar catalytic activity as platinum group noble metals. Thus far, the intrinsic thermodynamic properties and their relations with the local interfacial phenomena of such carbide−zeolite heterogeneous catalytic materials have rarely been explored. Here, employing high temperature oxide melt solution calorimetry, for the first time, we determined the energetics of molybdenum carbide (Mo 2 C) formation under confinement in zeolite Y (Mo 2 C/FAU) as a function of Si/Al ratio experimentally. As Si/Al ratio increases, the formation enthalpies of Mo 2 C/FAU from constituent oxides and carbides become less endothermic, spanning within a narrow range, between ∼0 and 10 kJ/mol TO 2 (tetrahedron unit). Confinement of refractory Mo 2 C in zeolite Y is energetically more favorable than encapsulation of MoO 3 in the same host, by more than ∼30 kJ/mol TO 2 . Such significant energetic differences between Mo 2 C/FAU and MoO 3 /FAU in formation enthalpies and the highly exothermic Mo 2 C−FAU guest−host interaction energies, highlight robust bonding at the carbide−zeolite interfaces that harnesses the refractory nature of Mo 2 C guest species, and compensate the energetic deficiency for achieving subnano-sized Mo 2 C particles.

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