The structure, thermal expansion coefficients and ionic conductivity of Ce 1-x Sm x O 2-x/2 and Ce 1-x Ca x O 2-x (x ) 0-0.30) solid electrolytes prepared hydrothermally in a relatively wide concentration range for the first time were systematically investigated. The uniformly small particle size (40-68 nm) of the hydrothermally prepared materials allows sintering of the samples into highly dense ceramic pellets at 1400 °C, a significantly lower temperature, compared to that at 1600 °C required for samples prepared by solid-state techniques. The maximum ionic conductivity was found at x ) 0.17 for the Sm and at x ) 0.09 for the Casubstituted ceria (σ 600 °C ) 5.7 × 10 -3 S/cm, E a ≈ 0.9 eV, and σ 600 °C ) 2.1 × 10 -3 S/cm, E a ≈ 0.8 eV, respectively). The thermal expansion coefficients, determined from high-temperature X-ray data, are 8.6 × 10 -6 and 9.4 × 10 -6 K -1 for the best conducting Ce 0.83 Sm 0.17 O 1.915 and Ce 0.91 Ca 0.09 O 1.91 solid electrolytes, respectively.

Faraday probes are a common plasma diagnostic used to determine the local ion charge flux of electric propulsion plumes. Standard practices, guidelines, and recommendations are provided for experimental methods and analysis techniques that aim to standardize community practices, to mitigate test environment effects, and to reduce systematic measurement error in order to improve plume predictions in the space environment. The approaches are applicable to time-averaged plasma properties in the near-field and far-field of electric propulsion plumes, with emphasis on Hall effect thrusters and gridded ion thrusters. Considerations for other electric propulsion technologies are provided, including electrosprays, arcjets, and electromagnetic thruster concepts. These test strategies are expected to increase the quality of comparisons between different thrusters and vacuum environments, thereby broadening the applicability of ground-based measurements and enhancing the fidelity for on-orbit predictions and modeling validation.

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