Spin Seebeck effect and phonon energy transfer in heterostructures containing layers of a normal metal and a ferromagnetic insulator

This is the final version. Available from the American Physical Society via the DOI in this recordIn the framework of the kinetic approach based on the Boltzmann equation for the phonon distribution function, we analyze phonon heat transfer in a heterostructure containing a layer of a normal metal (N) and a layer of a ferromagnetic insulator (F). Two realistic methods for creating a temperature gradient in such a heterostructure are considered: by heating the N layer by an electric current and by placing the N/F bilayer between massive dielectrics with different temperatures. The electron temperature Te in the N layer and the magnon temperature Tm in the F layer are calculated. The difference in these temperatures determines the voltage VISHE on the N layer in the Seebeck spin effect regime. The dependence of VISHE on the bath temperature and on the thickness of the N and F layers is compared with the available experimental data.European Union Horizon 202

Temperature dependence of the magnon-phonon energy relaxation time in a ferromagnetic insulator

This is the final version. Available from the American Physical Society via the DOI in this recordWe have used the Boltzmann kinetic equation for the phonon distribution function to analyze the relaxation kinetics of the spin system of a ferromagnetic insulator (F) lying on a massive dielectric substrate with high thermal conductivity. Under periodic heating of the spin system, the relaxation depends on the thickness of the F layer and on the frequency of the thermal source ω. When the thickness of the F layer is much greater than the phonon-magnon scattering length, the magnon temperature dependence on the frequency has two features related to specific characteristic times of the system. One of them determines the dependence in the low-frequency regime and is related to the average phonon escape time from the F layer to the substrate τes. In turn, the high-frequency behavior is determined by the magnon-phonon collisions time τmp. From the latter, the time of phonon-magnon collisions τpm can be found. In contrast, the response of effectively thin F layers is characterized by just one feature, which is determined by the time τmp. Thus, based on the obtained theoretical results, the times τes,τmp, and τpm can be deduced from experiments on the parametric excitation of spin waves by electromagnetic radiation modulated at frequency ω.European Union Horizon 202

High performance nanostructured bismuth oxide-cobaltite as a durable oxygen electrode for reversible solid oxide cells

The high reactivity between bismuth oxide and cobaltite oxygen electrodes is a bottleneck in developing active and reliable bismuth oxide–cobaltite composite oxygen electrodes for solid oxide cells (SOCs). Herein, a Sr-free Sm0.95Co0.95Pd0.05O3−δ (SmCPd) oxygen electrode decorated with nanoscale Er0.4Bi1.6O3 (ESB) is synthesized and assembled on a barrier-layer-free Y2O3–ZrO2 (YSZ) electrolyte film. The cell with the ESB decorated SmCPd composite oxygen electrode exhibits a peak power density of 1.81 W cm−2 at 750 °C and 0.58 W cm−2 at 650 °C. More importantly, excellent operating stability is achieved in the fuel cell mode at 600 °C for 500 h, and in electrolysis and reversible modes at 750 °C for over 200 h. The results demonstrate the feasibility of applying bismuth oxide–cobaltite composite oxygen electrodes in developing high-performance and durable SOCs

Effect of Pd doping on the activity and stability of directly assembled La0.95Co0.19Fe0.76Pd0.05O3-δ cathodes of solid oxide fuel cells

Sr doping is a common strategy to enhance the electrocatalytic activity of perovskite cathode materials of solid oxide fuel cells (SOFCs), but the tendency of Sr surface segregation, chemical incompatibility with yttria-stabilized zirconia (YSZ) and interaction with volatile contaminants such as chromium in SOFC stacks lead to a loss of long-term cell performance. Herein, a Sr-free and Pd-doped La 0.95 Co 0.19 Fe 0.76 Pd 0.05 O 3-d (LCFPd) cathode is directly assembled on a barrier-layer-free YSZ electrolyte cell without conventional high temperature pre-sintering. The cell with the directly assembled LCFPd-GDC (gadolinium-doped ceria) composite cathode exhibits a peak power density of 1035 mW cm - 2 and excellent operation stability at 750 °C for 200 h. Cathodic polarization significantly enhances the electrode/electrolyte interface contact, indicated by the substantial decrease of cell ohmic resistance from 0.28 O cm 2 to 0.14 O cm 2 after polarization at 500 mA cm - 2 and 750 °C for 120 h. Detailed elemental analysis indicates that doped Pd could be segregated on the electrode surface under fuel cell operation conditions, which significantly enhances the electrocatalytic activity for the O 2 reduction reaction. This study provides new strategy to develop cobaltite based perovskite materials directly on YSZ electrolyte