Thin-film nano-thermogravimetry applied to praseodymium-cerium oxide films at high temperatures

Abstract

High precision measurements of oxygen nonstoichiometry d in thin film metal oxides M a O b6d at elevated temperatures and controlled oxygen partial pressures p O2 are reported with the aid of resonant microbalances. The resonant microbalances applied here consisted of y-cut langasite (La 3 Ga 5 SiO 14 ) and CTGS (Ca 3 TaGa 3 Si 2 O 14 ) piezoelectric resonators, operated in the thickness shear mode at $5 MHz. Measurements of variations in d of Pr 0.1 Ce 0.9 O 2-d (PCO) films are reported for the oxygen partial pressure range from 10 À8 bar to 0.2 bar at 700 C, and these results were found to be in good agreement with previously reported oxygen nonstoichiometry d data derived from chemical capacitance studies. The PCO thin-films were deposited via pulsed laser deposition on both sides of the resonators, whose series resonance frequency was tracked, converted into mass changes and, finally, into nonstoichiometry. The nonstoichiometry was observed to reach a plateau as the oxygen partial pressure dropped below about 10 À5 bar, the behavior being attributed to the full reduction of Pr to the trivalent state. These resonators enable stable operation up to temperatures above 1000 C, thereby maintaining high mass resolution suitable for determining oxygen nonstoichiometry variations in thin films deposited on such resonators. For the given experimental conditions, a mass resolution of $50 ng was achieved at 700 C with the CTGS resonator.

In Situ Method Correlating Raman Vibrational Characteristics to Chemical Expansion via Oxygen Nonstoichiometry of Perovskite Thin Films

“…[11] Using a piezocrystal substrate, oxygen nonstoichiometry is measured by monitoring the mass change during an oxygen exchange experiment. [17,18] In such studies, however, the initial oxygen nonstoichiometry of the as-deposited thin film is ordinarily unknown. Turning to the contactless methods, optical absorption measures the coupling of the optical transmittance with the valence state of a transition metal or rare earth ion in the lattice (e.g.…”

Linking the Electrical Conductivity and Non-Stoichiometry of Thin Film Ce1−xZrxO2−δ by a Resonant Nanobalance Approach

“…Furthermore, the long-term stability of catalytic properties of CeO 2 at high temperatures is limited by the effect of thermal sintering and the deactivation of redox couple (aging) which reduce the oxygen storage capacity [ 3 , 14 , 15 , 16 , 17 ]. Upon the developing of ceria-based materials with tailored properties for use as the oxygen storage component in state-of-the-art TWCs, these drawbacks can be mitigated by extrinsic doping with other aliovalent (alkali, rare-earths, transition metals) or isovalent (Zr, Hf, Ti) metal cations to form solid solutions with functional point defects [ 14 , 15 , 16 , 17 , 18 , 19 , 20 , 21 , 22 , 23 , 24 , 25 , 26 ]. In this regard, the Zr-substituted ceria, i.e., Ce 1−x Zr x O 2−δ (henceforth, CZO), has attracted the increasing interest of automobile industry and researchers as potentially the most prospective catalyst material for TWCs [ 17 , 23 , 24 , 27 , 28 , 29 ].…”

“…The nanobalance approach for the direct thermogravimetric investigation of the non-stoichiometry of CZO thin films was utilized. The method allows for high-precision measurements with mass resolutions as low as few nanogramms [ 22 ], which are inaccessible by means of conventional thermogravimeters that are used to study bulk materials. Both the thermogravimetric characterization and measurements of electrical conductivity of CZO thin films were performed at temperatures from 600 to 900 °C in reducing and oxidizing conditions with precise control of oxygen partial pressures ( p O 2 ) in the range of 10 −24 –0.2 bar.…”

High-temperature stable piezoelectric transducers using epitaxially grown electrodes

“…For example, stoichiometric langasite (La 3 Ga 5 SiO 14 ; LGS) and catangasite (Ca 3 TaGa 3 Si 2 O 14 ; CTGS) are piezoelectrically excitable up to their melting point of 1473 and 1350 • C, respectively (Shimamura et al, 1996;Fritze et al, 2006;Suhak et al, 2016). Furthermore, they are stable down to oxygen partial pressures of p O 2 = 10 −21 bar at 600 • C and 10 −14 bar at 1100 • C (Fritze, 2010;Schulz and Fritze, 2008).…”