Non‐stoichiometry in Oxide Thin Films: A Chemical Capacitance Study of the Praseodymium‐Cerium Oxide System

Abstract

While the properties of functional oxide thin fi lms often depend strongly on their oxygen stoichiometry, there have been few ways to extract this information reliably and in situ. In this work, the derivation of the oxygen nonstoichiometry of dense Pr 0.1 Ce 0.9 O 2 − δ thin fi lms from an analysis of chemical capacitance obtained by impedance spectroscopy is described. Measurements are performed on electrochemical cells of the form Pr 0.1 Ce 0.9 O 2 − δ / Y 0.16 Zr 0.84 O 1.92 /Pr 0.1 Ce 0.9 O 2 − δ over the temperature range of 450 to 800 ° C and oxygen partial pressure range of 10 − 5 to 1 atm O 2 . With the aid of a defect equilibria model, approximations relate chemical capacitance directly to non-stoichiometry, without need for fi tting parameters. The calculated non-stoichiometry allows extraction of the thermodynamic constants defi ning defect generation. General agreement of these constants with bulk values derived by thermogravimetric analysis is found, thereby confi rming the suitability of this technique for measuring oxygen non-stoichiometry of thin oxide fi lms. Potential sources of error observed in earlier chemical capacitance studies on perovskite structured oxide fi lms are also discussed.

Electrochemical stability of (La,Sr)CoO3−δ in (La,Sr)CoO3−δ/(Ce, Gd)O2−δ heterostructures

“…in multilayer thin films stacked at the nanoscale, electronic and ionic properties at interfaces can also be mixed and enhanced by varying layer characteristics and new properties in such heterostructures come from lattice strain and interface mobility effects, resulting even in enhanced chemical stability. [16][17][18][19][20] MeOs such as oxygen defective cerium oxide (ceria) fluorite, CeO 2- , and cobalt-based perovskites are a good example of such tunability. Ceria is a MIEC under reducing atmospheres, where formation of oxygen vacancies are compensated by the formation of polaron defects due to Ce 4+ /Ce 3+ valence changes.…”

Origin and Tunability of Unusually Large Surface Capacitance in Doped Cerium Oxide Studied by Ambient‐Pressure X‐Ray Photoelectron Spectroscopy

“…Such a capacitance is likely a key property that makes ceria an excellent electrocatalyst and active catalyst support. Recently, electrochemical impedance spectroscopy (EIS) was employed to quantify the capacitance of ceria electrodes on yttria‐stabilized zirconia solid electrolytes . By varying the thickness of thin film electrodes, bulk and interfacial capacitances were isolated in Sm‐doped CeO 2−δ .…”

Thermal conductivity control by oxygen defect concentration modification in reducible oxides: The case of Pr0.1Ce0.9O2−δ thin films

“…As the sample was annealed in ever more reducing conditions (T1-T5), the oxygen vacancy concentration increased accordingly, with the quenched-in values obtained for d in samples T3 and T4 in excellent agreement with equilibrium values obtained previously by chemical capacitance. 18 At the higher pO 2 s characteristic of T1 and T2, the frozen in values for d were smaller than the equilibrium values due to partial reoxidation during cooling. The sample annealed in hydrogen (T5) was set as the reference oxygen vacancy concentration at d ¼ 0.05 (meaning that all of the Pr 4þ cations are reduced to Pr 3þ ).…”

“…The non-stoichiometry of these films was previously investigated and characterized by the authors with the aid of chemical capacitance measurements. 18 This work shows the ability to vary the thermal conductivity of a material by control of oxygen non-stoichiometry and thus points to the possibility for in situ control of phonon transport via control of the oxygen vacancy concentration. ; MTI Corporation, Richmond, CA) by pulsed laser deposition (PLD, Neocera, Inc.) from oxide targets.…”

“…The sample annealed in hydrogen (T5) was set as the reference oxygen vacancy concentration at d ¼ 0.05 (meaning that all of the Pr 4þ cations are reduced to Pr 3þ ). 18 The oxygen vacancy in the nominally undoped ceria film (T7) was estimated by assuming an acceptor impurity concentration of 100 ppm in the film, as is typical for these materials. 30 The thermal conductivities of the six samples with different oxygen vacancy concentrations are shown in Figure 2.…”