Technologia wytwarzania i właściwości multiferroikowej ceramiki typu PFN

Abstract

The character of the present paper is both technological-experimental and concerning research application. In (introductory) Part 1 there is presented the state of the investigation in ceramic ferroelectromagnetic materials. The materials in question, being ferroelectrics (antiferroelectrics/ ferrielectrics) and ferromagnetics (antiferromagnetics/ferrimagnetics), belong to a family of multiferroic smart materials. They are some of a chemical compounds and solid solutions of the different types of crystal structures, including: perovskites, bismuth oxides with layer-type structure, boracites, hexagonal manganites RMnO3, hexagonal fluorites BaMeF4, and some compounds of hexagonal BaTiO3. As a result of coupling, electronically and magnetically ordered ferroelectromagnetic subsystems display magnetoelectronic effect. It means that their spontaneous polarization as well as spontaneous magnetization can be changed by both external electric field and magnetic field. In the present work, multiferroic material PbFe1 xNbxO3 (PFN for short) underwent technological analysis, the main aim of which was reducing electrical conductivity and dielectric losses while keeping high value of electric permittivity and minimizing or completely eliminating the creation of, besides the perovskite phase, the second, undesired pirochlore phase. The aim of optimizing the chemical composition of PFN to reduce electrical conductivity was to receive the material displaying magnetic and electronic properties which would be electronic-field as well as magnetic-field controlled. The polarization process in ceramics demands application of the high-voltage electric field, which is why receiving PFN material of a low conductivity was crucial because it made the magnetoeletronic research possible. The goal of the research was finding the optimal composition of ceramics of the general formula PbFe1 xNbxO3 which had been modified through percentage change in Fe/Nb content. The basis of the analysis was also to search for the optimal technology of receiving the materials of the previously-mentioned composition. Simultaneously with choosing the ceramic composition characterized by best qualities, there were estimated the optimal conditions of technological process. The estimating concerned both the synthesis of PbFe1/2Nb1/2O3 (PFN12) by various methods (synthesis of powder in the solid phase, synthesis of powder in the liquid phase, powder synthesized by mechanical activation) and the modification (for example, the synthesis of powder by sintering the compacts with different kinds of priming, the synthesis by powder calcination, etc). The process of the PFN powder densification was also optimized. It was carried out by different methods (by free sintering and hot unixial pressing). The subsequent phase of PFN12 qualities’ optimizing consisted of introducing admixture into the base composition, in both isovalent and heterovalent manner. Different admixture’s chemical elements with various ionic radii sizes was substituted into the A position of the compound (the position of lead) as well as into the B position (iron/niobium). The possibility of increasing the coupling of magnetic and electronic system was also investigated by designing solid solutions based on various multiferroics. Combining them made possible the correlation of magnetic and electronic system in higher (plus) temperatures. In this part of the book, there were presented the results concerning solid solutions basing on (1 x)BiFeO3-(x)PbFe1/2Nb1/2O3 (BF i PFN). The present work also aimed at finding a PFN12-type material that would not contain lead (so-called unleaded material). Resultantly, a BaFe1/2Nb1/2O3 unleaded multiferroic material was obtained, in which, in the A position of the compound, lead has been completely replaced by bar, that is by highly polarizable cation. Designing chemical compositions of PFN-type was carried out under constant supervision of the particular phases of the technological process, which was based, among others, on crystallochemical as well as structural criteria. In optimizing the properties of PFN ceramics the used methods were derivatographic (DTA, TG), X-ray (XRD), the Mössbauer spectroscopy, microstructural method (SEM), energy-dispersive X-ray spectroscopy (EDS, EPMA), internal friction method (Q–1) as well as the results of dielectric, magnetic, piezoelectric, magnetoelectric, electromechanic and electric conductivity research.