# Magnetoelectric Composites: Engineering for Tunable Filters and Energy Harvesting Applications
## 3 Results
The EDS analyses of the P-F multiferroic composites are presented in Figure 3a-f (according to [37]), and the given values are the average values from five measurement areas. The calculations of the theoretical (t) and experimental (ex) results of oxides in the composite composition are summarized in Table 1. The EDS investigation confirmed no presence of foreign elements. In the case of compositions with a predominant ferroelectric phase content, high compliance with the theoretical calculations for individual composite compositions is observed. In the case of compositions with a predominant content of the magnetic phase, the analysis showed an excess content of the magnetic ferrite phase. The electron probe microanalyses (EPMA) represent the distribution of the composite elements on the surface of the multiferroic ceramic sample. Figure 3g shows a representative EPMA analysis for the 90P-10F composite sample. The maps of individual elements show an increase in signal detection intensity in areas richer in this element and vice versa. As a result, the obtained map provides a complete picture of the distribution of the magnetic and ferroelectric components on the surface of the composite sample. In the case of the elements with the lowest content, the measurement is the least accurate. The EPMA complies with SEM imaging using the BSE technique (Figure 1f), confirming the effectiveness of both methods of microstructure analysis. The full EPMA results for multiferroic P-F composites are presented in [37]. The X-ray diffraction patterns of the multiferroic composites tested at room temperature are presented in Figure 4. The analysis showed the presence of firm peaks in the ferroelectric phase (coexistence of two tetragonal and rhombohedral phases) and the magnetic phase (ferrite). In the case of the P ferroelectric phase, the best match was obtained for the card no. 00-33-0784 (for the tetragonal crystal system with space group P4 mm) and the card no. 01-073-2022 (for the rhombohedral crystal system with space group R3m). On the other hand, the best match for ferrite materials (F) was obtained from the JCPDS data 08-0234 (for the spinel phase with space group Fd-3m). Depending on the change in individual components, a change in the intensity of individual reflections is observed. The dielectric measurements presented in previous work [37] showed that in the tested material, there is a clear tendency for the electrical loss to increase with an increase in the ferromagnetic phase content. However, such a tendency is not reflected in the subsequent permittivity spectra. To explain the reasons for the above dielectric phenomena, impedance spectroscopy (IS) was implemented to study the local maxima behavior of P-F multiferroic composites. IS test is a very effective tool for thoroughly analyzing the relaxations in many materials [47]. Figure 4: X-ray diffraction patterns for the P-F multiferroic composites (according to [37]). Figure 5 shows the complex impedance plots of \(Z^{\prime\prime}\) versus \(Z^{\prime}\) (Cole-Cole plots) from the temperature range 40-400 \({}^{\circ}\)C of the investigated ceramics with 10, 15, 20, 40, 60, and 80% ferrite content. For lower ferrite content samples, i.e., 10, 15, and 20% (P90-F10, P85-F15, P80-F20) samples), we had to numerically separate the not apparent semicircles on the plots at each temperature because the two semicircular arcs were very close due to similar grain and grain boundary impedance levels. We assigned the separated high-frequency arc to the grain interior, and the low-frequency arc to the grain boundary [48]. Completely different spectra were recorded for the samples with a higher ferrite content. Mainly two well separated semicircular were recorded for the composites with 80, 60, and 40% ferrite content (P20-F80, P40-F60, and P60-F40), presented in Figure 5a-c, respectively. Such a shape indicates that the ferrite phase dramatically decreases the impedance of the grain interior, which is consistent with the dielectric measurements mentioned above [49; 50].