Skip to main content

TUneable Multiferroics based on oxygen OCtahedral Structures

Periodic Reporting for period 2 - TUMOCS (TUneable Multiferroics based on oxygen OCtahedral Structures)

Reporting period: 2017-01-01 to 2018-12-31

Development of new wireless and low energy consuming micro-sized sensors is extremely important because of the growing demands for effective monitoring of the operational status of mechanisms, environmental conditions, and safety systems (including those designed to avert terroristic threats). Materials that combine magnetic, polar, and elastic orders (so called multiferroics) are considered as active elements in various new-generation sensors. The main objective of this project was development of novel environmental friendly multiferroics based on metastable perovskites and on layered double hydroxides in which a cross-coupling between ferroic order parameters can be tuned by both internal and external factors. Such materials in forms of films and/or arranged layers find use as magnetic field sensors, sensors of deformation/shock, and environmental sensors. Since the objectives to prepare, characterize, optimize, and modify these novel multiferroic materials required consolidation of specialists of complementary expertise in Physics, Chemistry, and Material Science and Engineering, with access to and skills in using specific and unique equipment and facilities, the interdisciplinary network of teams with different scientific culture and ensuring the effective knowledge & expertise transfer has been formed.
The overall objectives of the project have been achieved. Novel approaches to predict, design and produce new magnetic and multiferroic materials: complex oxides with perovskite-type structure and layered double hydroxides have been suggested and proved. Although Bi-containing compositions were initially considered, it has been found that these approaches can be successfully applied to chemically diverse perovskite-related oxides and layered double hydroxides. The interdisciplinary network of the project has demonstrated its efficiency and a stable trend to extension via new projects and other collaboration schemes with new teams that conduct research in related areas.
New phases of metastable perovskites and layered double hydroxides have been obtained and thoroughly characterised using high-precision experimental methods and theoretical modelling.
The main findings are the following:
In the BiFeO3-BiScO3 solid solution system, annealing-stimulated irreversible transformations (conversion) of high-pressure stabilized phases have been revealed (Figure S1). The conversion stabilized phases have been demonstrated to represent unique polymorphs with remarkable properties, which cannot be obtained by other methods. A special term – conversion polymorphism – has been introduced to denote the annealing-stimulated irreversible transformations of high-pressure stabilised phases. It has been shown that conversion polymorphism is a general phenomenon which can be found in large families of perovskite-related oxygen-octahedral structures. A remarkable feature of the systems where such a phenomenon occurs is that the pattern of the phase diagram depends on the maximum annealing temperature. This implies that by means of controlled annealing, materials with different combinations of the perovskite phases are obtained. Such a feature can be used to design new materials with morphotropic phase boundary.
Magnetic behaviour of Co(II)-Al layered hydroxides has been explained and modelled in terms of characteristic distortions of oxygen octahedra and freezing of the tilting fluctuations of the O-H bonds (Figure S2). The obtained results contribute to understanding of the mechanisms of magnetic phenomena in 2-D systems and, in particular, in layered double hydroxides, and forms a physical basis for potential application of layered materials as tuneable nano-magnets.
Early stage researchers were involved in all the actions of the project. Three summer schools, six workshops and 14 group trainings were organised within the scope of the project. The project achievements and results have been published in 35+ papers in peer-reviewed scientific journals and reported in 52 communications at 35 international conferences.
96.3% of the planned secondments have been implemented.
The obtained results contribute to a global goal of discovery of the high-added value technological products by means of development of new approaches to preparation, optimization and application of novel multifferroic materials. Such materials meet the requirements of ecological compatibility and recyclability. There is a good potential for application of these materials as thin films and arranged 2-D structures in micro-sized sensors.
Figure S1. State diagram the BiFe1-yScyO3 system and the conversion-stabilised phases.
Figure S2. Distortions of oxygen octahedra and freezing of OH-bonds fluctuations in Co-Al LDHs.