Thermodynamics of gaseous strontium and calcium cerates studied by Knudsen effusion mass spectrometry and estimation of relative electron ionization cross‐section for CeO2(g)

Rationale Ceria‐based systems are of great interest because of their unique properties. Such systems may be used as anode materials for SOFCs or in oxygen sensors. The exploitation of these materials often requires high temperatures. In such conditions, the partial or complete evaporation of materials is possible. Therefore, knowledge of the values of partial pressures and thermodynamic properties is essential to predict and/or prevent possible consequences and accidents. Methods Knudsen effusion mass spectrometry was used to determine partial pressures of vapor species over the SrO–CeO 2 and CaO‐CeO 2 systems. Measurements of partial pressures were performed with a MS‐1301 mass spectrometer. Vaporization was carried out using molybdenum or tungsten effusion cells. A theoretical study of gaseous strontium and calcium cerates was performed by several quantum chemical methods: density functional theory (DFT) M06, DFT PBE0, and MP2. Results The minimum value of relative electron ionization cross‐section for CeO 2 was estimated. In the temperature range of 2218–2249 K above the SrO‐CeO 2 system and of 2128–2208 K above the CaO‐CeO 2 system, gaseous M, MO, MO, CeO 2 , O, O 2 and MCeO 3 (M = Sr, Ca) were found. Energetically favorable structures of gaseous SrCeO 3 and CaCeO 3 were found, and vibrational frequencies were evaluated in the “rigid rotor‐harmonic oscillator” approximation. On the basis of the equilibrium constants of gaseous reaction MO + CeO 2 = MCeO 3 , the standard formation enthalpy of gaseous SrCeO 3 (−913 ± 26 kJ/mol) and of gaseous CaCeO 3 (−917 ± 26 kJ/mol) at 298 K were determined. Conclusions The estimated value of relative electron ionization cross‐section for CeO 2 is in agreement with the general rule applicable for dioxides. The stability of SrCeO 3 and CaCeO 3 gaseous species was confirmed by KEMS. Gas‐phase reactions involving gaseous SrO (CaO) and CeO 2 with gaseous SrCeO 3 (CaCeO 3 ) were studied. Enthalpy of formation reaction of gaseous SrCeO 3 (CaCeO 3 ) from gaseous SrO (CaO) were evaluated theoretically, and the obtained value is in agreement with the experimental one.