Preparation of spinel oxide layers for high temperature fuel cell applications

Oxide mit Spinellstruktur wurden durch thermische Oxidation metallischer dünner Schichten im System Mn-Co-Fe hergestellt und charakterisiert. Dazu wurden die metallischen Schichten mit unterschiedlichen Mn/Co/Fe Verhältnissen durch das Magnetron Co-sputter-Verfahren auf oxidierte Siliziumwafer und auf den ferritischen Edelstahl ZMG232L (Hitachi Metals Ltd.®) abgeschieden. Die Schichteigenschaften als Funktion der Glühatmosphäre (an O2 und Luft), der Temperatur und der Zeit wurden untersucht. Um die Eignung der Spinellschichten als mögliche Schutzschicht für metallische Interconnects der Hochtemperatur-Brennstoffzelle abzuschätzen, wurden Flächenwiderstandsmessungen durchgeführt und das Cr Diffusions/Transportverhalten aus dem Stahlsubstrat durch die Spinellschicht analysiert (ToF-SIMS sputter Tiefenprofil und EDX). Mn50Co50 Schichten mit einer Dicke von 1 $\mu$m die auf vorbehandelte ZMG232L Substrate abgeschieden wurden, zeigten die besten Anwendungseigenschaften.Oxides with spinel structure were produced by thermal oxidation of metallic thin films (0.3 $\mu$m and 1 $\mu$m thickness) from the Mn-Co-Fe system. Metallic films with different Mn/Co/Fe ratios were deposited by magnetron co-sputtering on oxidised silicon wafers and on ZMG232L (Hitachi Metals Ltd.®) ferritic stainless steel and their properties as a function of annealing atmosphere, temperature and time were studied. In order to assess the suitability of these spinels as protective coatings for metallic interconnects for Solid Oxide Fuel Cells, area specific resistance measurements were performed, as well as the analysis of Cr transport through the coatings. The Mn:Co=50:50 (at.%) coating having 1 $\mu$m thickness and deposited on pre-annealed ZMG232L substrates showed the best properties for this application

Effect of the deposition conditions of platinum electrodes on their performance as resistive heating elements

The performance of different platinum electrodes used as resistive heating elements was studied. Pt films having different thickness were deposited by RF magnetron sputtering at room temperature followed by post-deposition annealing at 700 ºC or made in-situ at 700 ºC. The Pt films were deposited over oxidized silicon, using Ti or Zr buffer layers. The resistance dependence on temperature was studied by applying increasing currents (up to 2A) to the Pt films. Changes in the microstructure of the Pt films account for the changes in the temperature coefficient of resistance as a function of the deposition parameters. The maximum substrate temperature (675 ºC) was obtained when using 200 nm Pt films deposited at 700 ºC over Ti, with a power consumption of only 16 W

Anodization behaviour and basic property mapping in the aluminium-erbium system

A co-evaporation technique was used for depositing an Al-Er thin film combinatorial library on borosilicate glass substrates with Er concentrations between 3 and 21 at.% and a total compositional resolution of 0.25 at.% mm1. Scanning droplet cell microscopy was employed for compositional mapping of several fundamental properties of mixed oxides grown on Al-Er thin film alloys. Microstructural and crystallographic particularities of Al-Er alloys were identified along the library, and a relevant compositional threshold at around Al-5 at.% Er was identified. Further, small surface grains in the nanometre range were found at Al grain boundaries, and an initial amorphization and/or hexagonal phase nucleation was identified for Er amounts around 5 at.%. Electrochemical studies revealed the importance of this compositional threshold, as distinct maximizations of oxide formation factors and oxide electrical permittivities were observed.(VLID)346749

Identification of high-performance anodic memristors by combinatorial screening in hafnium-tantalum library

The metal-oxide- semiconductor technology (CMOS) has already reached its limits in terms of scaling, power consumption and processing speed. With this regard, the development of novel memory systems is vital. Memristive devices are scalable alternatives in the next generation of electronics showing non-volatile properties. Valve metals such as Hf and Ta are high-κ dielectric materials used for metal-insulator- metal architectures with the memory concept based on the resistive switching due to the nano-dimensional conductive filaments (CFs) formation inside of the insulating oxide. The aim of this study was to investigate the memristive behavior of devices based on pure Hf, Ta and their alloys which were sputtered as bottom electrodes onto the Si wafer. The total compositional spread of Hf-Ta library was ranging from 5 to 92 at.% Hf. The insulating layer with the thickness up to 20 nm was fabricated via simple, inexpensive and fast electrochemical anodization process. Hence, a high number of memristors was finalized by patterning Pt top electrodes. Electrical properties of devices were screened with 1 at.% resolution using self-developed Gantry robot revealing three different compositional zones with specific memory characteristics. The switching mechanism was confirmed by depth profile investigation by XPS and imaging of CFs by HRTEM. Nanofilaments differed in size, shape and position in the oxide for the devices based on Hf, Ta or their alloys. The produced memristors have shown remarkable improvement in their performance which may lead towards the development of defect engineered memristors applicable for artificial neural networks. [1] I. Zrinski, C.C. Mardare, L.-I. Jinga, J.P. Kollender, G. Socol, A.W. Hassel, A.I. Mardare, Phosphate incorporation in anodic hafnium oxide memristors, Appl. Surf. Sci. 548 (2021) 149093. https://doi.org/10.1016/j.apsusc.2021.149093. [2] I. Zrinski, C.C. Mardare, L.I. Jinga, J.P. Kollender, G. Socol, A. Minenkov, A.W. Hassel, A.I. Mardare, Electrolyte‐dependent modification of resistive switching in anodic hafnia, Nanomaterials. 11 (2021) 1–18. https://doi.org/10.3390/nano11030666. [3] I. Zrinski, A. Minenkov, C.C. Mardare, J.P. Kollender, S.A. Lone, A.W. Hassel, A.I. Mardare, Influence of electrolyte selection on performance of tantalum anodic oxide memristors, Appl. Surf. Sci. 565 (2021) 150608. https://doi.org/10.1016/j.apsusc.2021.150608

A Thermodynamic Approach for Selection of Anodizing Electrolytes in AluminiumHolmium System

In this paper, an approach is described for the electrolyte selection to grow optimally anodic films on thermally coevaporated aluminium and holmium combinatorial alloys. This method based on thermodynamic and electrochemical principles proves that electrolyte selection for anodizing of alloys having different microstructures and electrochemical behaviour of individual constituents can be decided by superimposing potentialpH diagrams of individual constituents of the alloy. For the application of this approach, the most widely investigated valve metal, aluminium, and a nonvalve metal rare earth, holmium, have been chosen as a model case. Based on selfconstructed EhpH diagrams and solubility data, suitable electrolytes and pH range leading to the formation of barriertype anodic films on aluminium and holmium as well as on their alloys are proposed.(VLID)4844497Version of recor

Downstream analytics quantification of ion release during high voltage anodisation of niobium

In operando quantification of field-assisted ion release during high-voltage anodisation (up to 100 V SHE) of Nb in 0.1 M sulphuric acid was performed. Electrochemical high-field oxide formation under both potential and current control was studied separately. The quantification of in situ ion release via ICP-MS revealed an increase of the oxide dissolution factor (from 337 to 422 fm V1) when decreasing the potential scan rate from 200 to 100 mV s1. Dissolution rates measured during galvanostatic oxide formation allowed measuring oxide dissolution factors of 719 and 837 fm V1 for current densities of 1.0 and 0.5 mA cm2, respectively. As compared to the potentiodynamic case, higher dissolution rates and oxide dissolution factors were measured for galvanostatic anodisation. The overall fraction of the charge used for generation of soluble Nb species was below 0.4% for all oxide growth regimes. Cross-sectional SEM imaging proofs an oxide formation factor of 2.1 nm V1. The surface of anodised films was extremely smooth and featureless without any cracks or voids. Based on X-ray diffraction, the films were found to be amorphous, indicating that no field crystallisation is occurring under the applied oxide growth conditions even at higher voltages.(VLID)340177

Basic properties mapping of anodic oxides in the hafniumniobiumtantalum ternary system

A thin film combinatorial library deposited by co-sputtering of Hf, Nb and Ta was employed to characterise fundamental properties of the Hf-Nb-Ta system. Compositional mappings of microstructure and crystallography revealed similarities in alloy evolution. Distinct lattice distortion was observed upon addition of hexagonal Hf, leading to amorphisation of alloys containing more than 32 at.% Hf and less than 27 and 41 at.% Nb and Ta, respectively. Volta potential and open circuit potential mappings indicated minimal values for the highest Hf concentration. Localised anodisation of the library by scanning droplet cell microscopy revealed valve metal behaviour. Oxide formation factors above 2 nm V1 were identified in compositional zones with high amounts of Nb and Ta. Fitting of electrochemical impedance spectroscopy data allowed electrical permittivity and resistivity of mixed oxides to be mapped. Their compositional behaviours were attributed to characteristics of the parent metal alloys and particularities of the pure oxides. MottSchottky analysis suggested n-type semiconductor properties for all HfNbTa oxides studied. Donor density and flat-band potential were mapped compositionally, and their variations were found to be related mainly to the Nb amount. Synergetic effects were identified in mappings of Hf-Nb-Ta parent metals and their anodic oxides.(VLID)341510

Corrosion and Structural Properties of ErbiumZinc Thin Films at LowtoMedium Erbium Concentrations

A combinatorial erbiumzinc thin film material library is deposited by thermal coevaporation. The library is screened for its structural and compositional properties by energydispersive Xray (EDX), Xray diffraction (XRD), and scanning electron microscopy (SEM), and shows a compositional range from 3.1 to 31.2at% Er. XRD proofs an amorphous region around 20at% Er. This is rarely encountered in binary systems, and supports an improved corrosion resistance for this composition. SEM shows the formation of a compact film at the same compositional range. The alloys' electrochemical characteristics are assessed with opencircuit potential (OCP), electrochemical impedance spectroscopy (EIS), cyclic voltammetry, and potentiodynamic polarization measurements in a scanning droplet cell microscopy (SDCM) setup coupled with an inductively coupled plasma optical emission spectrometer (ICPOES). This allows capturing the relation between current, potential, and metal ion dissolution in the system. The experiments are performed in aqueous 0.01m Na2SO4 solution under constant flow (0.0136mLs1). Increased corrosion resistance is found for alloys containing 1922at% in all four used methods, showing the superior properties at this compositional range.(VLID)4918838Version of recor

Revisiting Electronic Topological Transitions in the Silver–Palladium (Ag_<i>c</i>Pd_1−<i>c</i>) Solid Solution: An Experimental and Theoretical Investigation

Multiple thick film samples of the AgcPd1−c solid solution were prepared using physical vapour deposition over a borosilicate glass substrate. This synthesis technique allows continuous variation in stoichiometry, while the distribution of silver or palladium atoms retains the arrangement into an on-average periodic lattice with smoothly varying unit cell parameters. The alloy concentration and geometry were measured over a set of sample points, respectively, via energy-dispersive X-ray spectroscopy and via X-ray diffraction. These results are compared with ab initio total energy and electronic structure calculations based on density functional theory, and using the coherent potential approximation for an effective medium description of disorder. The theoretically acquired lattice parameters appear in qualitative agreement with the measured trends. The numerical study of the Fermi surface also shows a variation in its topological features, which follow the change in silver concentration. These were related to the electrical resistivity of the AgcPd1−c alloy. The theoretically obtained variation exhibits a significant correlation with nonlinear changes in the resistivity as a function of composition. This combined experimental and theoretical study suggests the possibility of using resistivity measurements along concentration gradients as a way to gain some microscopic insight into the electronic structure of an alloy