Study of the Polarization Behavior of Ce_0.9Gd_0.1O_2-δSingle Crystals below 350°C to Room Temperature

Abstract

Single crystalline ceria samples with the composition Ce0.9Gd0.1O2-δ were pre-polarized with ±5 V for up to 300 s using a Pt coated AFM tip as working electrode. The direct contact zone had a diameter of < 50 nm. Subsequently, the effect of the polarization on the surface potential of the samples was investigated by mapping the introduced defect gradient and its decay with time using Kelvin probe force microscopy. The generated surface potential gradients were found to have a diameter of up to 1 µm, which is explained by the local ionization of defect associates by the applied high electric field. Measurements were performed at room temperature and 50 °C. The polarization behavior of the Ce0.9Gd0.1O2-δ single crystals was compared to cyclovoltammetry and polarization-relaxation experiments at T ≤ 350°C and in dry air or nitrogen which were performed using a specially suited AFM (Controlled Atmosphere High Temperature Scanning Probe Microscope CAHT-SPM by Semilab).

Measurement of polarization effects in dual-phase ceria-based oxygen permeation membranes using Kelvin probe force microscopy

“…In contrast to positive polarization, polarizing the sample with a negative bias referring to the AFM tip led to a lowered surface potential in the direct vicinity of the contact, which is in good accordance with the results previously published for singlephase ceria materials [21][22][23][24][25]. Similar to the effect observed with +1 V polarization, polarization with a tip bias of −1 V led in some cases to a parallel oxidation effect of an area adjacent to the contact area (Figure 5).…”

“…Similar to KPFM-based polarization-relaxation analyses performed for single-phase ceria materials [21][22][23][24][25], positive polarization of CSO grains in the CSO-FC2O composite with a tip bias of +3 V led to a locally increased surface potential reaction, which decreased over time.…”

“…The surface potential gradient was also shown to be reversible over time as long as the applied voltage was kept in a certain range. The time dependence was shown to vary with dopant concentration (e.g., abundance of oxygen vacancies in ceria) and also depends on the ratio of grain boundary/grain bulk [22][23][24][25]. Single ceria grains in a mixed ion/electronconductive composite have so far not been addressed by AFMbased electrochemical studies.…”

“…In a subsequent mapping experiment, the AFM tip was used as Kelvin probe to scan the locally changed surface potential distribution at the sample surface until the original state was reached again. In this way, polarization-induced, reversible surface potential changes have already been monitored for a variety of single-phase acceptordoped ceria materials [21][22][23]. Time-resolved relaxation curves calculated from the KPFM images can be used to determine room temperature diffusion coefficients [24].…”

Room Temperature Polarization Phenomena in Nanocrystalline and Epitaxial Thin Films of Gd-Doped Ceria Studied by Kelvin Probe Force Microscopy

“…[19][20][21] A combination of surface potential mapping using Kelvin probe force microscopy (KPFM) and polarization experiments has recently been established as experimental technique to access polarization properties of oxide ion conductors at low temperatures. 7,[22][23][24] In contrast to more established measurement techniques, surface potential mapping using Kelvin probe force microscopy has a very high spatial resolution, thus yielding not only information about the effect of polarization but also about size and intensity of the introduced chemical gradient and velocity of the relaxation process.…”