The implementation of nano-engineered composite oxides opens up the way towards the development of a novel class of functional materials with enhanced electrochemical properties. Here we report on the realization of vertically aligned nanocomposites of lanthanum strontium manganite and doped ceria with straight applicability as functional layers in high-temperature energy conversion devices. By a detailed analysis using complementary state-of-the-art techniques, which include atom-probe tomography combined with oxygen isotopic exchange, we assess the local structural and electrochemical functionalities and we allow direct observation of local fast oxygen diffusion pathways. The resulting ordered mesostructure, which is characterized by a coherent, dense array of vertical interfaces, shows high electrochemically activity and suppressed dopant segregation. The latter is ascribed to spontaneous cationic intermixing enabling lattice stabilization, according to density functional theory calculations. This work highlights the relevance of local disorder and long-range arrangements for functional oxides nano-engineering and introduces an advanced method for the local analysis of mass transport phenomena.

Cuprous oxide (Cu₂O) is a promising p-type semiconductor material for many applications. So far, the lowest resistivity values are obtained for films deposited by physical methods and/or at high temperatures (~1000 °C), limiting their mass integration. Here, Cu₂O thin films with ultra-low resistivity values of 0.4 Ω.cm were deposited at only 260 °C by atmospheric pressure spatial atomic layer deposition, a scalable chemical approach. The carrier concentration (7.10¹⁴−2.10¹⁸ cm⁻³), mobility (1–86 cm²/V.s), and optical bandgap (2.2–2.48 eV) are easily tuned by adjusting the fraction of oxygen used during deposition. The properties of the films are correlated to the defect landscape, as revealed by a combination of techniques (positron annihilation spectroscopy (PAS), Raman spectroscopy and photoluminescence). Our results reveal the existence of large complex defects and the decrease of the overall defect concentration in the films with increasing oxygen fraction used during deposition.

The exploitation of interface effects turned out to be a powerful tool for generating exciting material properties. Such properties include magnetism, electronic and ionic transport and even superconductivity. Here, instead of using conventional homogeneous doping to enhance the hole concentration in lanthanum cuprate and achieve superconductivity, we replace single LaO planes with SrO dopant planes using atomic-layer-by-layer molecular beam epitaxy (two-dimensional doping). Electron spectroscopy and microscopy, conductivity measurements and zinc tomography reveal such negatively charged interfaces to induce layer-dependent superconductivity (T_c up to 35 K) in the space-charge zone at the side of the planes facing the substrate, where the strontium (Sr) profile is abrupt. Owing to the growth conditions, the other side exhibits instead a Sr redistribution resulting in superconductivity due to conventional doping. The present study represents a successful example of two-dimensional doping of superconducting oxide systems and demonstrates its power in this field.

In the last few years, high temperature solid oxide electrolysis cells (SOECs) have emerged as a promising solution for energy conversion and storage. However, state-of-the-art systems suffer from technological limitations, which prevent their widespread use and market penetration. Particularly, the electrode–electrolyte interface represents a critical element due to the high oxygen potential located in this area, which in turn determines interface delamination. In this context, the use of mesoporous materials, whose architecture is characterized by concatenated nanometric-size pores and high specific surface area, represents a powerful strategy toward the achievement of long-term stability of the electrode. Such structures have been recently proposed as ionically conducting electrode scaffolds for solid oxide fuel cells (SOFCs), exhibiting good performances and low degradation rates. In particular, it has been shown that a highly increased triple phase boundary (TPB)-active points distribution along the electrode may be achieved upon infiltration with a catalytically active material. In this study, infiltrated mesoporous cerium was used as a functional oxygen electrode layer in a fuel electrode supported SOEC system. The results indicate that an enhancement in both long-term stability and electrolysis cell performance are achieved. This is attributed to the decrease in high current density paths and areas of high oxygen potential and to the superior thermal stability of such a nanostructured composite, which allows better current distribution. First, the morphological characterization of the as-synthesized mesoporous Ce_0.8Gd_0.2O_1.9 (CGO), which was carried out by TEM microscopy and low-angle X-ray diffraction (LA-XRD), is presented. A structural and functional investigation of the fuel electrode supported cells, in which the oxygen electrode is composed of catalytically active La_0.6Sr_0.4Co_0.2Fe_0.8O₃ (LSCF) infiltrating a CGO scaffold, was studied by means of XRD, scanning electron microscopy and spectroscopy, and electrochemical measurements. Characterization under co-electrolysis mode (45% H₂O, 45% CO₂ and 10% H₂) shows an injected current density higher than 1.2 A cm⁻² at 1.4 V at 750 °C. Electrochemical impedance spectroscopy was carried out at regular time intervals during galvanostatic (0.5 and 0.75 A cm⁻²) long-term operation for 1400 h, exhibiting a decrease in polarization resistance and only slight increase in serial resistance during operation. Total degradation rates lower than 2% kh⁻¹ at 0.5 A cm⁻² and 1% kh⁻¹ at 0.75 A cm⁻² were obtained. Finally, a mechanism for cell degradation based on evolution of the fuel electrode is proposed.

In this paper we present the atomic-layer-by-layer oxide molecular beam epitaxy (ALL-oxide MBE) which has been recently installed in the Max-Planck Institute for Solid State Research and we report on its present status, providing some examples that demonstrate its successful application in the synthesis of different layered oxides, with particular reference to superconducting La₂CuO₄ and insulator-to-metal La_2−xSr_xNiO₄. We briefly review the ALL-oxide MBE technique and its unique capabilities in the deposition of atomically smooth single-crystal thin films of various complex oxides, artificial compounds and heterostructures, introducing our goal of pursuing a deep investigation of such systems with particular emphasis on structural defects, with the aim of tailoring their functional properties by precise defects control.

We report a new strategy to grow nano-columnar La ₂ NiO ₄ thin films with an enlarged specific surface area. In combination with modifications of the surface chemistry, we strongly improved the oxygen exchange activity of this promising electrode material.