High-Temperature Thermoelectricity in LaNiO₃–La₂CuO₄ Heterostructures

Abstract

Transition metal oxides exhibit a high potential for application in the field of electronic devices, energy storage, and energy conversion. The ability of building these types of materials by atomic layer-by-layer techniques provides a possibility to design novel systems with favored functionalities. In this study, by means of the atomic layer-by-layer oxide molecular beam epitaxy technique, we designed oxide heterostructures consisting of tetragonal KNiF-type insulating LaCuO (LCO) and perovskite-type conductive metallic LaNiO (LNO) layers with different thicknesses to assess the heterostructure-thermoelectric property-relationship at high temperatures. We observed that the transport properties depend on the constituent layer thickness, interface intermixing, and oxygen-exchange dynamics in the LCO layers, which occurs at high temperatures. As the thickness of the individual layers was reduced, the electrical conductivity decreased and the sign of the Seebeck coefficient changed, revealing the contribution of the individual layers where possible interfacial contributions cannot be ruled out. High-resolution scanning transmission electron microscopy investigations showed that a substitutional solid solution of La(CuNi)O was formed when the thickness of the constituent layers was decreased.

Beyond Coherent Oxide Heterostructures: Atomic‐Scale Structure of Misfit Dislocations

“…Depending on the mismatch between the two constituent oxides, these materials have varying degrees of strain at the heterointerface, which also alters the atomic structure and stability. Accordingly, oxide heterostructures can lead to diverse atomic and electronic structures at the interface with extraordinary properties, including those exhibiting enhanced radiation tolerance, ferromagnetism, superconductivity, superionic conduction, thermoelectricity, and photocatalysis, In oxide heterostructures, additional aspects that are altered at the interfaces are the chemical composition and stoichiometry, which depend on the processing conditions as well as the atomic‐layer chemistry of the two oxides that are married. Therefore, a vast spectrum of structures is possible at oxide heterostructures.…”

Design of Complex Oxide Interfaces by Oxide Molecular Beam Epitaxy

“…This length scale is comparable with the critical length of elemental intermixing, while for the thick LNO layer, the structural ( Fig. 6e) and also the chemical abruptness of the interfaces has been visualized, when the nominal LNO layer thickness is locked to eight unit cells [91].…”

“…For this, we measure the electrical conductivity of a single LCO film in the temperature interval 300 K < T < 800 K (see Fig. 3) [91]. The decrease of the electrical conductivity at 300 K < T < 500 K (region 1) is ascribed to the loss of non-equilibrium interstitial oxygens, which, accordingly, results in a decrease of the number of holes.…”

“…An intriguing example with contacts of insulating 214-LCO and metallic 113-LaNiO 3 (113-LNO) multilayers (Fig. 6b) has been recently studied for examining the thermoelectric and transport properties [91]. The dependency of the transport properties on the thickness of the constituent layers was revealed.…”

Precise control of atoms with MBE: from semiconductors to complex oxides

“…The adaptable perovskite structure of TM oxides offers constructing them in different forms, such as ultrathin films or heterostructures [9], but also leads to diverse physical properties ranging from HTSC [10][11][12] to thermoelectricity [13]. In other words, engineering of epitaxial oxides grants unlimited combinations of multilayers delivering a fundamental playground for device fabrication and possible applications.…”