RESUMEN
High-temperature piezoelectric materials, which enable the accurate and reliable sensing of physical parameters to guarantee the functional operation of various systems under harsh conditions, are highly demanded. To this end, both large piezoelectricity and high Curie temperature are pivotal figures of merit (FOMs) for high-temperature piezoceramics. Unfortunately, despite intensive pursuits, it remains a formidable challenge to unravel the inverse correlation between these FOMs. Herein, a conceptual material paradigm of multiscale structural engineering was proposed to address this dilemma. The synergistic effects of phase structure reminiscent of a polymorphic phase boundary and refined domain morphology simultaneously contribute to a large piezoelectric coefficient d33 of 30.3 pC/N and a high Curie temperature TC of 740 °C in (LiCeNd) codoped Na0.5Bi2.5Nb2O9 (NBN-LCN) ceramics. More encouragingly, the system has exceptional thermal stability and is nonsusceptible to mechanical loading. This study not only demonstrates that the high-performance and robust NBN-LCN high-temperature piezoceramics hold great potential for implements under harsh conditions but also opens an avenue for integrating antagonistic properties for the enhancement of the collective performance in functional materials.
RESUMEN
Enhancing the performance of thermoelectric materials is demanded to develop strategies for introducing multidimensional microstructures into materials to induce full-scale phonon scattering while ensuring electrical transport performance. Herein, a previously unreported rhombohedral h-SnTe (R3Ìm) has been achieved in the nanoscale dimension by the electron beam irradiation of ß-SnTe (Fm3Ìm) materials. The h-SnTe structure contains interlayer van der Waals gaps and exhibits metallic behavior evaluated by density-functional theory calculations, which coherently appears in the narrow-band semiconductor ß-SnTe matrix. Our results provide a strategy for modifying the properties of SnTe-based thermoelectric materials and designing nanostructured chalcogenide heterostructures via electron beam irradiation.
RESUMEN
Magnetic oxide films with a strong anomalous Hall effect (AHE) have attracted much attention due to their strong sensitivity and high polarization for magnetic sensor applications. However, the linearity of the anomalous Hall sensors still needs improving. In this work, we propose to use the interface regulation to improve the linearity of the AHE. We grow spinel ferrite Co0.2Fe2.8O4 (CoFeO) thin films on MgAl2O4 (MAO) substrates and alter their interfacial properties by inserting a graphene layer between the MAO substrate and the CoFeO film. Through a detailed structure and performance analysis, it reveals that the insertion of graphene has not broken the epitaxial nature of the films but endows the film with a nanopillar-like structure. A series of electrical tests show that the Hall resistance signal of our thin film system has high sensitivity and high linearity to the magnetic field. Reduced hysteresis and better linearity of the anomalous Hall resistance were found in the graphene-inserted heterostructure due to differences in the nanostructure and possibly interfacial coupling. These results suggest that interfacial engineering offers a pathway to tune the performance of ferrite thin film systems for sensor applications.
RESUMEN
An atomic-scale understanding of nanoscale precipitates in thermoelectric materials will help us explore their microstructure-property relationship, providing a strategy to optimize their thermoelectric properties. In thermoelectric ß-SnTe, using advanced electron microscopy techniques, self-aligned nanoscale precipitates have been identified as γ-SnTe ultrathin nanosheets that induce anisotropic strain in the ß-SnTe matrix. The interlayer van der Waals interactions occur across the interface of γ-SnTe ultrathin nanosheets and the ß-SnTe matrix. The phase transition from γ-SnTe ultrathin nanosheets to ß-SnTe can be accomplished by in situ electron-beam irradiation that lays out an approach for tuning the properties of SnTe-based thermoelectric materials.
RESUMEN
Heteroepitaxial oxide-based nanocomposite films possessing a variety of functional properties have attracted tremendous research interest. Here, self-assembled vertically aligned nanocomposite (Pr0.5Ba0.5MnO3)1-x:(CeO2)x (x = 0.2 and 0.5) films have been successfully grown on single-crystalline (001) (La,Sr)(Al,Ta)O3 substrates by the pulsed laser deposition technique. Self-assembling behavior of the nanocomposite films and atomic-scale interface structure between Pr0.5Ba0.5MnO3 matrix and CeO2 nanopillars have been investigated by advanced electron microscopy techniques. Two different orientation relationships, (001)[100]Pr0.5Ba0.5MnO3//(001)[1-10]CeO2 and (001)[100]Pr0.5Ba0.5MnO3//(110)[1-10]CeO2, form between Pr0.5Ba0.5MnO3 and CeO2 in the (Pr0.5Ba0.5MnO3)0.8:(CeO2)0.2 film along the film growth direction, which is essentially different from vertically aligned nanocomposite (Pr0.5Ba0.5MnO3)0.5:(CeO2)0.5 films having only (001)[100]Pr0.5Ba0.5MnO3//(001)[1-10]CeO2 orientation relationship. Both coherent and semi-coherent Pr0.5Ba0.5MnO3/CeO2 interface appear in the films. In contrast to semi-coherent interface with regular distribution of interfacial dislocations, interface reconstruction occurs at the coherent Pr0.5Ba0.5MnO3/CeO2 interface. Our findings indicate that epitaxial strain imposed by the concentration of CeO2 in the nanocomposite films affects the self-assembling behavior of the vertically aligned nanocomposite (Pr0.5Ba0.5MnO3)1-x:(CeO2)x films.
RESUMEN
The magnetic and electrical properties of complex oxide thin films are closely related to the phase stability and cation ordering, which demands that we understand the process-structure-property relationships microscopically in functional materials research. Here we study multiferroic thin films of double-perovskite La2NiMnO6 epitaxially grown on SrTiO3, KTaO3, LaAlO3 and DyScO3 substrates by pulsed laser deposition. The effect of epitaxial strains imposed by the substrate on the microstructural properties of La2NiMnO6 has been systematically investigated by means of advanced electron microscopy. It is found that La2NiMnO6 films under tensile strain exhibit a monoclinic structure, while under compressive strain the crystal structure of La2NiMnO6 films is rhombohedral. In addition, by optimizing the film deposition conditions a long-range ordering of B-site cations in La2NiMnO6 films has been obtained in both monoclinic and rhombohedral phases. Our results not only provide a strategy for tailoring phase stability by strain engineering, but also shed light on tuning B-site ordering by controlling film growth temperature in double-perovskite La2NiMnO6 films.
RESUMEN
Epitaxial Pr0.5Sr0.5CoO3 thin films have been grown on single-crystalline (La0.289Sr0.712)(Al0.633Ta0.356)O3(001) substrates by the pulsed laser deposition technique. The magnetic properties and microstructure of these films are investigated. It is found that Ruddlesden-Popper faults (RP faults) can be introduced in the films by changing the laser repetition rate. The segregation of Pr at the RP faults is characterized by atomic-resolution chemical mapping. The formation of the RP faults not only contributes to the epitaxial strain relaxation but also significantly decreases the ferromagnetic long-range order of the films, resulting in lower magnetizations than those of the fault-free films. Our results provide a strategy for tuning the magnetic properties of cobalt-based perovskite films by modifying the microstructure through the film growth process.
