Anode-supported thin electrolyte cells are studied by electrochemical impedance spectroscopy (EIS). The aim is to describe how the losses of this type of cells are distributed at low current density (around open-circuit voltage) as a function of temperature. An equivalent circuit consisting of an inductance, a serial resistance <mml:math display="inline"><mml:mrow><mml:mo>(</mml:mo><mml:msub><mml:mi>R</mml:mi><mml:mi>s</mml:mi></mml:msub><mml:mo>)</mml:mo></mml:mrow></mml:math>(Rs) , and five arcs to describe the polarization resistance is suggested. This equivalent circuit is based on previous studies of single electrodes in three-electrode and two-electrode symmetric cell setups. The equivalent circuit components have been assigned to the electrode processes, and the assignments were verified by extensive full cell studies in which the partial pressure of reactant gases on both the electrodes as well as temperature was systematically varied with the aim to identify frequency regions which are dominated by an electrode specific process. Furthermore, the model is applied on a good performing cell with area specific resistance <mml:math display="inline"><mml:mrow><mml:mo>(</mml:mo><mml:mi>ASR</mml:mi><mml:mo>)</mml:mo><mml:mo>=</mml:mo><mml:mn>0.15</mml:mn><mml:mspace width="0.3em"></mml:mspace><mml:mi mathvariant="normal">Ω</mml:mi><mml:mspace width="0.3em"></mml:mspace><mml:msup><mml:mi>cm</mml:mi><mml:mrow><mml:mn>2</mml:mn></mml:mrow></mml:msup></mml:mrow></mml:math>(ASR)=0.15Ωcm2 at <mml:math display="inline"><mml:mrow><mml:mn>850</mml:mn><mml:mo>°</mml:mo><mml:mi mathvariant="normal">C</mml:mi></mml:mrow></mml:math>850°C and a poor performing cell with <mml:math display="inline"><mml:mrow><mml:mi>ASR</mml:mi><mml:mo>=</mml:mo><mml:mn>0.29</mml:mn><mml:mspace width="0.3em"></mml:mspace><mml:mi mathvariant="normal">Ω</mml:mi><mml:mspace width="0.3em"></mml:mspace><mml:msup><mml:mi>cm</mml:mi><mml:mrow><mml:mn>2</mml:mn></mml:mrow></mml:msup></mml:mrow></mml:math>ASR=0.29Ωcm2 at the same temperature. Both cells were fabricated using nominally the same procedure. The EIS analysis indicated that the difference in performance originates from microstructural differences on the cathode. This is further supported by the observation of large differences in the cathode microstructure by scanning electron microscope.

The spin-wave spectrum of Heisenberg spin clusters of various structures (bcc, fcc, and disordered) ranging in size between 9 and 749 spins is calculated by a self-consistent diagonalization of the equation of motion of ${\mathit{S}}^{+}$ in real space. The spin-wave spectrum of the clusters is strongly modified relative to the bulk, and the consequent neutron-scattering cross section exhibits discretely spaced wave-vector-broadened eigenstates. The implications of the finite size on thermodynamic properties, like the temperature dependence of the magnetization and the critical temperature, are also elucidated. We find the temperature dependence of the cluster magnetization to be well described by an effective power law, ${\mathit{M}}_{\mathrm{mean}}$∝1-${\mathit{BT}}^{\mathrm{\alpha }}$, with a size-dependent, but structure-independent, exponent larger than the bulk value. The critical temperature of the clusters is calculated from the spin-wave spectrum by a method based on the correlation theory and the spherical approximation generalized to the case of finite systems. A size-dependent reduction of the critical temperature by up to 50% for the smallest clusters is found. The trends found for the model clusters are extrapolated to the size regime of nanoscale particles.

The degradation behavior of anode supported solid oxide fuel cells (SOFCs) was investigated as a function of operating temperature and current density. Degradation rates were defined and shown to be mainly dependent on the cell polarization. The combination of a detailed evaluation of electrochemical properties by impedance spectroscopy, in particular, and post-test microscopy revealed that cathode degradation was the dominant contribution to degradation at higher current densities and lower temperatures. The anode was found to contribute more to degradation at higher temperatures. Generally, the degradation rates obtained were lower at higher operating temperatures, even at higher current densities. A degradation rate as low as <mml:math display="inline"><mml:mrow><mml:mn>2</mml:mn><mml:mo>%</mml:mo><mml:mo>∕</mml:mo><mml:mn>1000</mml:mn><mml:mspace width="0.3em"></mml:mspace><mml:mi mathvariant="normal">h</mml:mi></mml:mrow></mml:math>2%∕1000h was observed at <mml:math display="inline"><mml:mrow><mml:mn>1.7</mml:mn><mml:mspace width="0.3em"></mml:mspace><mml:mi mathvariant="normal">A</mml:mi><mml:mo>∕</mml:mo><mml:msup><mml:mi>cm</mml:mi><mml:mrow><mml:mn>2</mml:mn></mml:mrow></mml:msup></mml:mrow></mml:math>1.7A∕cm2 and <mml:math display="inline"><mml:mrow><mml:mn>950</mml:mn><mml:mo>°</mml:mo><mml:mi mathvariant="normal">C</mml:mi></mml:mrow></mml:math>950°C over an operating period of <mml:math display="inline"><mml:mrow><mml:mn>1500</mml:mn><mml:mspace width="0.3em"></mml:mspace><mml:mi mathvariant="normal">h</mml:mi></mml:mrow></mml:math>1500h .

Samples of interacting nanosized maghemite particles have been studied by Mössbauer spectroscopy and magnetization measurements. The apparent blocking temperatures obtained from Mössbauer spectroscopy and zero-field-cooled magnetization curves are nearly identical, but the values obtained from measurements of the decay of remanence are much lower. These results are not in accordance with the Néel model for superparamagnetic relaxation, but can be explained by the formation of an ordered spin-glass-like state at low temperatures. At a critical temperature a transition to a superparamagnetic state takes place. By varying the average interparticle distance it is possible to change the ordering temperature.