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For the last decades, energy harvesters based on piezoelectricity from mechanical vibration (wind, human activities, vibrations of machines and traffic, ocean waves, and acoustic waves) are explored extensively for its functionality in energy technologies. Typical applications that could benefit from mechanical energy harvesting are that many sensors, alarms, LED lights, and other low-power and ultra-low-power devices can be driven energetically completely independently [1]. To fabricate a flexible piezoelectric energy harvester (FPEHs) that operates under various conditions, ceramic particles were blended with a polymer to form composite films. Two-phase lead-free BaZr0.2Ti0.8/PVDF and lead-based PbZr0.52Ti0.48/PVDF piezocomposites, as well as three-phase PbZr0.52Ti0.48/Ni0.7Zn0.3Fe2O4/PVDF composites films with variable filler content (up to 50 vol.%) have been prepared by hot pressing method. Structure and morphology of piezo-active phase powders as well as distribution of filler in obtained flexible films were characterized by XRD and SEM analysis. Total amount of electroactive phase (% FEA) of PVDF in all films were investigated by FTIR analysis. In all composites dielectric permittivities was increased in contrast to their polymer PVDF host matrix, but also displayed decreased breakdown strength and raised energy loss. In addition, the remnant polarization (Pr) and leakage current were also investigated to evaluate the breakdown strength in all types of flexible films. Also, ferromagnetic response was established in PZT/ferrite/PVDF films under magnetic field of 10 kOe. Calculations of storage energies and output voltage obtained for the investigated materials revealed an increasing trend with increasing amount of active phase. The maximum storage energy of 0.42 J/cm3 at 390 kV/cm3 was obtained for PZT-PVDF (40-60) films while the maximum output voltage of about 10 V was obtained for PZT-PVDF (50-50) flexible film. In addition, comparisons between properties o

To investigate the effect of synthesis procedure and sintering temperature on the functional properties of perovskite/spinel ceramics, BaTiO3/CoFe2O4 composites were prepared by thermal decomposition, coprecipitation, and microemulsion method, and sintered at 1150°C and 1300°C. The phase composition and morphology of as-prepared powders as well as sintered ceramics were thoroughly examined by X-ray powder diffraction (XRPD) and scanning electron microscopy (SEM) coupled with electron dispersive spectroscopy (EDS). The dielectric and ferroelectric measurements were performed in detail. Generally, the samples sintered at 1300°C had better performances than those sintered at 1150°C. The composite synthesized by thermal decomposition and sintered at 1300°C stands out among other prepared BaTiO3/CoFe2O4 ceramics, owing to high stability in the wide frequency range and low leakage currents. The obtained results indicate that such composite might be successfully applied as a functional multiferroic.

The paper presents the realization of an experimental setup used for testing energy harvesting and storage devices based on the use of lead-free bismuth sodium titanate-barium titanate (NBT-BT) in combination with polyvinylidene fluoride (PVDF) polymer. PVDF is a polymer matrix in which piezoelectric phase is dispersed and enables formation of flexible films by hot pressing method. The paper presents an electromechanical model of a typical PVDF module, generates a simulation model, and presents simulation results. The experimental setup is based on a mechanical excitation for generating pulses of an force of different amplitude and duration, applied on the aforementioned energy harvesting NBT-BT-PVDF devices, likewise, on an electronic assembly for measuring the pulses of electrical quantities (current and voltage), that are generated at the output electrodes. The research in this paper is predominantly experimental and it shows the obtained oscilloscope recordings of the excitation force and output voltage of energy harvesting modules at different modes and conditionsof mechanical excitation. After this, a comparison of the simulation and experimental results is made.

To investigate the effect of synthesis procedure and sintering temperature on the functional properties of perovskite/spinel ceramics, BaTiO3/CoFe2O4 composites were prepared by thermal decomposition, coprecipitation, and microemulsion method, and sintered at 1150°C and 1300°C. The phase composition and morphology of as-prepared powders as well as sintered ceramics were thoroughly examined by X-ray powder diffraction (XRPD) and scanning electron microscopy (SEM) coupled with electron dispersive spectroscopy (EDS). The dielectric and ferroelectric measurements were performed in detail. Generally, the samples sintered at 1300°C had better performances than those sintered at 1150°C. The composite synthesized by thermal decomposition and sintered at 1300 °C stands out among other prepared BaTiO3/CoFe2O4 ceramics, owing to high stability in the wide frequency range and low leakage currents. The obtained results indicate that such composite might be successfully applied as a functional multiferroic.

To investigate the influence of spinel structure and sintering temperature on the functional properties of BaTiO3/NixZn1−xFe2O4 (x = 0, 0.5, 1), NiFe2O4, ZnFe2O4, and Ni0.5Zn0.5Fe2O4 were in situ prepared by thermal decomposition onto BaTiO3 surface from acetylacetonate precursors. As-prepared powders were additionally sintered at 1150 °C and 1300 °C. X-ray powder diffraction (XRPD) and scanning electron microscopy (SEM) coupled with electron dispersive spectroscopy (EDS) were used for the detailed examination of phase composition and morphology. The magnetic, dielectric, and ferroelectric properties were investigated. The optimal phase composition in the BaTiO3/NiFe2O4 composite, sintered at 1150 °C, resulted in a wide frequency range stability. Additionally, particular phase composition indicates favorable properties such as low conductivity and ideal-like hysteresis loop behavior. The favorable properties of BaTiO3/NiFe2O4 make this particular composite an ideal material choice for further studies on applications of multi-ferroic devices.

In order to examine the influence of phase composition and sintering temperature on the functional properties of perovskite/spinel composites, BaTiO3/NixZn1−xFe2O4 (x = 0, 0.5, 1), NiFe2O4, ZnFe2O4, and Ni0.5Zn0.5Fe2O4 were in situ prepared by thermal decomposition onto BaTiO3 surface. Acetylacetonate complexes were used as the precursors. The obtained powders were compressed to pellets and sintered at 1150 °C and 1300 °C. X-ray powder diffraction (XRPD) and scanning electron microscopy (SEM) coupled with electron dispersive spectroscopy (EDS) were used for the comprehensive investigation of phase composition and morphology. The magnetic, dielectric, and ferroelectric properties were performed in detail. The optimal phase composition was found in the BaTiO3/NiFe2O4 composite sintered at 1150 °C, which resulted in a wide frequency range stability. Furthermore, particular phase composition led to suitable properties such as low conductivity and ideal-like hysteresis loop behavior [1]. These functional properties of BaTiO3/NiFe2O4 make this composite a “material of choice“ for further studies on applications of multiferroic devices., U cilju ispitivanja uticaja faznog sastava i temperature sinterovanja na funkcionalna svojstva perovskit/spinel kompozita BaTiO3/NixZn1−xFe2O4 (x = 0, 0,5, 1), NiFe2O4, ZnFe2O4, i Ni0,5Zn0,5Fe2O4 pripremljeni su in situ metodom termalne dekompozicije. U sintezi su korišćeni acetilacetonatni kompleksi kao prekursori. Dobijeni prahovi su komprimovani u tablete i sinterovani na 1150 °C i 1300 °C. Za detaljno ispitivanje faznog sastava i morfologije sintetisanih kompozita korišćene su metode rendgenske difrakcije praha (XRPD) i skenirajuće elektronske mikroskopije (SEM) spregnute sa energetsko disperzivnom spektroskopijom (EDS). Ispitivana su i magnetna, dielektrična i feroelektrična svojstva sinterovanih kompozita. Ustanovljeno je da optimalni fazni sastav pronađen kod kompozita BaTiO3/NiFe2O4 sinterovanog na 1150 °C dovodi do stabilnosti u širokom opsegu frekvencija. Optimalni fazni sastav pomenutog kompozita povoljno je uticao na funkcionalna svojstva kao što su niska provodnost i feroelektrično ponašenje koje se ogleda u zadovoljavajućem izgledu histerezisa [1]. Ova svojstva nedvosmisleno ukazuju da je kompozit BaTiO3/NiFe2O4 odgovarajući izbor za dalja istraživanja posvećena primeni multiferoičnih materijala.

For the last several decades, energy harvesters based on piezoelectricity from mechanical vibration have emerged as very promising devices that are being explored extensively for their functionality in energy technologies. In this paper, a series of flexible lead-free BaZr0.2Ti0.8O3 (BZT)/PVDF and lead-based PbZr0.52Ti0.48O3 (PZT)/PVDF piezocomposites with variable filler content up to 50 vol% were prepared by a hot pressing method. The structure and morphology of the BZT and PZT powders, as well as the distribution of the piezo-active filler in the obtained flexible films were characterized by XRD and SEM analysis. In addition, the remnant polarization (Pr) and leakage current were also investigated to evaluate the breakdown strength in both types of flexible films. The calculations of storage energies and output voltage obtained for the investigated materials revealed an increasing trend with an increasing amount of BZT and PZT active phases. The maximum storage energy of 0.42 J/cm3 (and energy efficiency of 40.7 %) was obtained for the PZT–PVDF (40–60) films, while the maximum output voltage of about 10 V (~10 µA) was obtained for the PZT–PVDF (50–50) flexible film. In addition, a comparison between the properties of the lead-based and lead-free flexible films, as well as the potential use of these films as energy storage and energy harvesting systems were analyzed.

Bismuth ferrite (BiFeO3) powders were synthesized by auto-combustion method. To decrease the quantity of active phase and improve the specific surface area, composites of BiFeO3 and natural porose materials (diatomaceous earth and cuttlebone) were prepared by chemical method from solution and calcined at low temperature. Such obtained powders were used as adsorbents and photocatalysts in methylene blue water solutions. Nature of photocatalysis under visible and UV-Vis light was examined under different pH conditions and presence of hydrogen peroxide, dissolved iron(III), oxalates and some other ions. Methylene blue is capable to absorb sunlight and insert electrons into semiconductor, so possibility of this way achieved dye-sensitization was studied [1]. Composites expressed better properties than individual components confirming the synergetic effect [2]. Acidic conditions were more suitable for decolorization, so possible Fenton reaction based homogeneous catalysis was also considered.

The idea of this work is finding the way to efficiently and safely use mechanical energy released in small quantities around us to power up small-scale electronic devices used in everyday life. To this purpose, flexible lead-free piezoelectric composite films were prepared by hot pressing. Different amounts (30, 35 and 40 vol%) of lead-free piezoelectric material bismuth sodium titanate-barium titanate were embedded in the matrix of polyvinylidene fluoride under carefully optimized conditions of temperature and pressure, obtaining flexible films with quite homogeneous distribution of piezo-active filler. ATR-FTIR analysis revealed that hot pressing the flexible films caused a transformation of electro-inactive PVDF alpha-phase into electro-active beta and gamma phases. Dielectric measurements showed an increase of the permittivity up to 80 with the active phase increasing. Anelastic measurements showed that the elastic modulus increases as well with the fraction of active ceramic phase. Lastly, obtained flexible polymer-composites demonstrated notable properties both for energy storage and energy harvesting application, showing up to 74% of energy storage efficiency and, from testing of the force impact, up to 9 V and similar to 80 mu W of output voltage and power.

Multiferroic composites containing ferroelectric Ba(Ti0.80Zr0.20)O-3 (BT80Zr20) phase and magnetic Ni0.7Zn0.3Fe2O4 (NZF), CoFe2O4 (CF) or Ni0.7Cu0.01Sm0.05Zn0.29Fe1.95O4 (NCuSmZF) phase were investigated in this study. Three composites, BT80Zr20-NZF, BT80Zr20-CF and BT80Zr20-NCuSmZF were prepared by mixing chemically synthesized powders in the planetary mill, uniaxial pressing and sintering at 1300 degrees C. X-ray diffraction data for the single phase and composites ceramics indicated the formation of crystallized structure of both ferrites and barium zirconium titanate, without the presence of undesirable phases. Microstructure analysis has shown the formation of two types of nanosized grains, polygonal ferromagnetic and rounded ferroelectric grains. Non-saturated hysteresis loops were evident in all composite samples possibly due to the presence of very high conductive ferrite phases. The BT80Zr20-CF has shown the lowest conductivity values in comparison with other two compounds and therefore the highest potential for ferroelectric application. The impedance investigations confirmed the presence of different relaxation processes that originate from the grain and grain boundary contributions. Investigation of J-E relation between leakage and electric field for the BT80Zr20 and composites revealed the presence of four possible mechanisms of conduction in these materials.

Multiferroic composites with general formula Ba(Ti0.95Zr0.05)O-3 - Ni0.7Zn0.3Fe2O4, Ba(Ti0.95Zr0.05)O-3 - CoFe2O4, Ba(Ti0.95Zr0.05)O-3 - Ni0.7Cu0.01Sm0.05Zn0.29Fe1.95O4, (BTZr(95-5) - NZF, BTZr(95-5) - CF, BTZr(95-5) - NCuSmZF) were prepared by mixing chemically obtained different types of ferrites and BTZ(95-5) powders in the planetary mill for 24 h. The optimization of sintering process was performed and powders were pressed and sintered at 1300 degrees C for obtained composites samples. From the X-ray analysis for single phase and composites ceramics the formation of crystallized structure of ferrites and barium zirconium titanate can be noticed. SEM analyses indicated the formation of two types nanosized grains, polygonal ferromagnetic and rounded ferroelectric grains. The electrical properties of these materials were investigated using impedance spectroscopy and analysis of ferroelectric measurements. Impedance analysis of all investigated samples has shown different relaxation processes that originated from the grain and grain boundary contributions. The results of polarization vs. electric field measurements have shown the influence of magnetic phase type and its concentration on the ferroelectric properties of the composites. Due to high conductivity of ferrite phases and presence of interfacial polarization, the shapes of these curves differed from the conventional ferroelectric materials.

Bismuth ferrite (BiFeO3) is studied a lot in recent years because of its specific structure and potential to act as single phase multiferrioic well above the room temperature. Thanks to the optical band gap energy of 2.3- 2.8 eV BiFeO3 is also an interesting material for photocatalytic and solar energy applications. Sol-gel and solid state methods were used to synthesize BiFeO3-based powders. Two main methods would be used to modify the band gap. First one is incorporation into composite materials with contribution of phase boundaries formed between different phases of bismuth-iron oxides or BiFeO3 and silica-based substrate powders. Second one is modification of powders by milling them with organic compounds in order to get defects and oxygen vacancies. Composition, structure and microstructure of such way obtained powders were conducted and their influence on variations in band-gap energy studied. Visible and UV-Vis light photocatalytic activity of synthesized materials for decomposition of methylene blue solutions was tested and optimal composition and preparation route for this application proposed, as well as the present mechanisms of adsorption and photocatalytic reaction.

The search for multiferroic materials combining electric and magnetic properties in a single phase has attracted a lot of attention in the perspective of future magnetoelectronic devices. A handful of single phase multiferroics have been discovered so far, and most of them are not suitable for practical applications at present, either because the room temperature polarization/magnetization is too small or their mutual coupling is too weak. One of the most important single-phase multiferroic material with Aurivillius structure is Bi5Ti3FeO15 (BFT) which generally yields a magnetoelectric coupling above room temperature. The main lack of this material is high electrical conductivity and hence the lower ferro-electromagnetic properties. Since BFT has the capability to host ions of different size, multiferroic properties could be improved by using dopants or ionic substitutions on different A and B-sites of the structure. To this respect, Co2+ and Y3+ doped BFT were prepared by the solid state reaction method according to formulas: Bi1-xYxTi3FeO15 (x=0.1, 0.2, 0.3) and BiTi3Fe1-yCoyO15(y=0.1, 0.3, 0.5). Slightly improve of ferroelectric properties was noticed with 0.3 mol% of Co while replacement of Bi3+ with Y3+ causes a reduction in orbital hybridization between Bi 6sand O 2s/2porbitals leading to a decrease in electric polarization as a vector sum of all dipole moments. Magnetic measurements confirm the antiferromagnetic nature of pure and Y doped ceramics while Co-doped samples exhibit a typical ferromagnetic loop reveals the existence of FM interactions in these samples. The largest Mr value appears in samples doped with 3 mol% of Co (Mr of 0.084 emu/g and Hc of 287 Oe). Raman spectroscopy confirmed that Y prefer to replace Bi ions in the pseudo-perovkite layers while Co ions enter into the lattice and occupy the Fe site inside of oxygen octahedral.

Composites based on barium titanate and nickel zinc ferrite doped with cooper and samarium were prepared by a mixing method. The formation of barium titanate tetragonal crystal structure and nickel zinc ferrite cubic spinel structure was identified. Polygonal grains were formed in all three types of ceramics. Due to the very high conductivity of ferrite phase in the materials the ferroelectric hysteresis loops were roundish and not typical for classical ferroelectric material. The break down field was found to be similar for all compositions. Leakage current measurements have shown the existence of different types of conductivity mechanisms in each material. The impedance analysis suggested a bit stronger impact of grain boundaries on total conductivity of the composites and the mechanism of polaronic conduction of two types. The magnetization of the composites is lower than for the pure ferrite phase and corresponds to the weight fraction of the ferrite phase. The soft magnetic nature of these composites might be very useful for development of multifunctional devices which will be able to switch the magnetization with small external magnetic field. Humidity sensing properties of the prepared ceramics were also investigated.

Multiferroic composites with general formula Ba(Ti0.95Zr0.05)O3–Ni0.7Zn0.3Fe2O4/ CoFe2O4/Ni0.7Cu0.01Sm0.05Zn0.29Fe1.95O4, (BTZr(95-5)–NZF/CF/NCuSmZF) were prepared by mixing chemically obtained different types of ferrites and BTZ(95-5) powders in the planetary mill for 24 h. The optimization of sintering process was performed and powders were pressed and sintered at 1300 °C for obtained composites samples. From X-ray analysis for single phase and composites ceramics can be noticed the formation of crystallized structure of ferrites and barium zirconium titanate. SEM analyses indicated the formation of two types nanosized grains, polygonal ferromagnetic and rounded ferroelectric grains. The electrical properties of these materials were investigated using impedance spectroscopy and analysis of ferroelectric measurements. Impedance analysis of all investigated samples has shown different relaxation processes that originated from the grain and grain boundary contributions. The results of polarization vs. electric field measurements have shown the influence of magnetic phase type and its concentration on the ferroelectric properties of the composites. Due to high conductivity of ferrite phases and presence of interfacial polarization, the shapes of these curves differed from the conventional ferroelectric materials.

Bismut ferrite powder was prepared by sol-gel method. It was calcined at 600 °C and then milled in order to break agglomerates and eventually obtain ceramic samples of high density. Such way treated powders were pressed uniaxially under 196 MPa and sintered at 800 °C. Conventionaly sintered samples were heated by the rate of 10 °C/min and furnace cooled. Other samples were inserted into preheated oven and/or taken out from the hot oven directly to air or water at room temperature. Influence of heating and cooling rates on structure, microstructure and electrical properties were studied. Reducing the processing time in temperature interval between 447 °C and 767 °C prevents formation of secondary phases, but the effect on phase composition is not large. It is significantly easier to notice the effect on electrical properties.

One of the most important single-phase multiferroic materials with Aurivillius structure is Bi5Ti3FeO15 (BFT) which generally yields a magnetoelectric coupling above room temperature with a magnetoelectric coefficient of 10 mV/cmOe [1]. It has a special interest in this family of compounds because it is a combination of multiferroic BiFeO3 and ferroelectric Bi4Ti3O12 and can be used as new magnetoelectric material for different devices. Years of intensive research have shown that the main lack of this material is high electrical conductivity and hence the low ferro-electromagnetic properties. This is a common problem in single-phase multiferroics, in general. Although they are expected to produce an applications breakthrough, they show poor properties at room temperature. Since BFT has the capability to host ions of different size, multiferroic properties could be improved by using dopants or ionic substitutions on different A and B-sites within the perovskitelike layers [2]. Insertion of magnetic ion such as Co3+ at B-sites could increase the remnant magnetization in BFT ceramics while Y3+ could enhance the dielectric and ferroelectric properties. To this respect, Co2+ and Y3+ doped BFT were prepared by the solid state reaction method according to formulas: Bi1-xYxTi3FeO15 (x = 0.1, 0.2, 0.3) and BiTi3Fe1-yCoyO15 (y = 0.1, 0.3, 0.5). XRD data confirm the formation of singlephase Aurivillius compounds. SEM micrographs show an evident decrease in grain size of Co modified ceramics in comparison with pure BFT while there is no particular change of the grain size with Y doping. The ferroelectric and magnetic properties of all ceramic composites were also studied. Raman spectroscopy in dependence of temperature was used to give an insight to the possible ferroelectric character of BFT and also the way that dopants could influence the structural mechanism affecting the material’s properties at the main magnetic and ferroelectric transitions.

Bismuth ferrite (BiFeO3) and bismuth titanate ferrite (Bi5Ti3FeO15) are studied a lot in recent years because of their specific structure and potential to act as single phase multiferrioics. Thanks to the optical band gap energy of 2.3-2.8 eV for BiFeO3 and 1.8- 2.3 eV for Bi5Ti3FeO15, these materials are also interesting for photocatalytic and solar energy applications, and studies of using Bi5Ti3FeO15 for this purpose are very rare. Solgel methods were used to produce BiFeO3 and BiFeO3-modified diatomaceous earth, while Bi5Ti3FeO15 was obtained sol-gel and solid-state methods. These powders were characterized, and their visible light photocatalytic activity for decomposition of methylene blue was tested in acidic, close-to-neutral and alkaline conditions. Fenton-like catalysis was also tested. Influence of synthesis method, microstructure, and catalyst composition on dye degradation will help in proposing the mechanism of adsorption and photocatalytic processes.

Bismuth-ferrite (BiFeO3) is studied a lot in recent years due to its specific multiferroic properties. Thanks to the optical bandgap energy of 2.3-2.8 eV [1], BiFeO3-based materials are also interesting for photocatalytic and solar energy applications. Sol-gel methods were used to produce BiFeO3 and BiFeO3-modified diatomaceous earth. These powders were characterized, and their visible light photocatalytic activity for decomposition of some organic dyes was tested in acidic, close-to-neutral and alkaline conditions. Fenton-like catalysis was also tested for those materials. Influence of synthesis method, microstructure, ageing and composition on dye degradation helped in proposing the mechanism of adsorption and photocatalytic processes.

Multiferroics are a class of multifunctional materials (a single phase or multiphase/composite materials) characterized by the coexistence of at least two ferroic orders (ferroelectric, ferromagnetic, or ferroelastic). Numerous multiferroics are being developed during the years of intensive research. As compounds with good ferroelectric and piezoelectric properties, barium titanate based materials are usually used as a constituent of these composites and nickel ferrite based materials as a constituent with magnetic properties [1]. The nickel ferrite combines wide range of useful magnetic properties with relatively low electrical conductivity and high value of magnetization. In order to improve electrical and magnetic properties of this material it is usually doped with Jahn-Teller ions such as zinc, manganese or copper [1,2]. Composite ceramics prepared by mixing barium titanate (BT) and nickel zinc (NZF) ferrite doped with Cu and Sm in different mass ratios, BT-NZCSF/70-30, BT-NZCSF/80-20 and BT-NZCSF/90-10 were sintered at 1080 °C for 4 h. The formation of barium titanate tetragonal crystal structure and nickel zinc ferrite cubic spinel structure was identified. Polygonal grains of both constituents were homogeneously distributed in the ceramic samples. Ferroelectric hysteresis loops were roundish and not typical for classical ferroelectric material due to high conductivity of ferrite phase in the materials. The composition with the highest concentration of BT possessed the lowest value of leakage current density. Impedance spectroscopy analysis has shown that total resistivity of the BTNZCSF/ 70-30 composition is the lowest due to the highest concentration of conductive ferrite phase in the system. Temperature dependence of the grain and grain boundary conductivity was analyzed using the Arrhenius equation. The activation energies were approximately from 0.2 eV up to 0.5 eV, suggesting the mechanism of polaronic conduction of both, n and p types. When investigate

BaTiO3 nanopowders doped with La and co-doped with La/Mn were prepared by auto-combustion and Pechini methods, respectively. The influence of the synthesis methods, dopants and sintering temperature on the BaTiO3 structure and its potential to be used as humidity and/or H-2 gas sensor were studied. The optimization of all process parameters was performed to obtain adequate microstructure for the development of good sensor properties. The difference in the grain size between the La-doped and La/Mn co-doped samples and the formation of different types of defect structures in these ceramics were found to be significant for the desired electrical and ferroelectric properties. The La-doped ceramics with a pseudo-cubic structure showed the highest potential for gas sensors. The materials obtained by the Pechini method had a tetragonal structure and showed the best response, i.e., the change in electrical resistivity by four orders of magnitude in the humid atmosphere.

Ni-Zn ferrites, with the general formula Ni1-xZnx Fe2O4 (x = 0.0, 0.3, 0.5, 0.7, 1.0), CoFe2O4, BaTiO3 and PbZr0.52Ti0.48O3 powders were synthesized by auto-combustion method. The composites were prepared by mixing the appropriate amounts of individual phases, pressing and conventional sintering. X-ray analysis, for individual phase and composites, indicated the formation of crystallized structure of Ni1-xZnx Fe2O4, BaTiO3 and PbZr0.52Ti0.48O3 without the presence of secondary phases or any impurities. SEM analyses indicated a formation of uniform grain distribution for ferromagnetic and ferroelectric phases and formation of two types of grains, polygonal and rounded, respectively. Magneto-dielectric effect was exhibited in all samples because of the applied stress occurring due to the piezomagnetic effect and the magnetic field induced the variation of the dielectric constant. For all samples the dielectric constant was higher in applied magnetic field. At the low frequency, the dispersion of dielectric losses appeared, while at the higher frequency the value of tan ffi become constant (Maxwell-Wagner relaxation). Investigation of J-E relation between leakage and electric field revealed that both nickel zinc ferrite and composites have three different regions of conduction: region with ohmic conduction mechanism, region with the trap-controlled space charge limited current mechanism and region with space charge limited current mechanism.

Multiferroic materials exhibit at least two of the so-called ferroic properties (ferroelectric, (anti)ferromagnetic and ferroelastic) in the same time. They are very interesting from the theoretical point of view because of a different nature of those properties, but coupling between the properties opens up huge possibilities for application as magnetoresistors, memory devices, sensors and many other devices [1]. Being ferroelectric up to 830 °C and antiferromagnetic (weakly ferromagnetic) up to 370 °C, bismuth ferrite (BiFeO3) is one of the very few room-temperature singlephase multiferroic materials and one of the most studied ceramic materials in the last two decades. BiFeO3 has also good potential to be used as a pigment, catalyst, photocatalyst or solar cell material [1,2]. However, because of specific obstacles in obtaining pure, dense and highly resistive ceramics, harnessing of those properties is still far from being achieved and the possibility of its application as a multiferroic material is arguable. High volatility of bismuth above 800 °C and thermodynamic instability of BiFeO3 between 447 °C and 767 °C make the densification of BiFeO3 ceramics very difficult, especially by conventional methods. High leakage currents in BiFeO3 (originating mostly from oxygen and bismuth vacancies) disable ceramic samples to be polarized and to exhibit ferroelectric properties. Spiral structure of magnetic moments lowers the coupling between ferroelectric and magnetic orders [3,4]. BiFeO3 ceramic materials presented in this study were synthesized by autocombustion method with idea to lower the temperature needed for effective sintering in order to prevent volatilisation and improve the density and phase composition. Auto-combustion is a type of sol-gel route which enables high homogeneity in solutions stabilized by organic compounds, which oxidize vigorously producing the ash powders as a wanted product. Because of such fast reaction, the defects are incorporated into st

The composite materials mixed with soft polymers present a new class of materials with specific electric, magnetic, and mechanical properties. Organic materials used as a polymer matrix in these composites possess low electrical conductivity, high chemical stability, and low processing temperature. Among the most common polymer matrices, PVDF and P(VDF-TrFE) are marked as an ideal candidates due to their piezoelectric and ferroelectric features. Review of selected examples of complex composites based on ferroics or multiferroics embedded in polymeric matrix is presented.

Di-phase ceramic composites, with general formula xNi(0.7)Zn(0.3)Fe(2)O(4) - (1-x)BaTiO3(x = 0.9, 0.7, 0.5, 0.3, 0.1), were prepared by a mixing method. X-ray analysis, for powder and ceramics, indicated the formation of ferrite and barium titanate phases without the presence of the impurities. SEM analysis indicated that the composite morphology contained two types of grains, polygonal and rounded. Homogeneous microstructure and the smallest grain size were obtained in ceramics with 70% of barium titanate. The electrical properties of these materials were investigated using impedance spectroscopy, dielectric and ferroelectric measurements. The NZF-BT(30-70) composite has shown better electrical properties in comparison to other investigated ceramics, confirmed by dielectric and ferroelectric data analysis. Saturation magnetization and coercive field decreased with the increase of the content of ferroelectric phase.

Comparative study of different PZT-based composite materials ((x)PbZr0.52Ti0.48O3 + (1-x)CoFe2O4 and (x) PbZr0.52Ti0.48O3 + (1-x)Ni0.7Zn0.3Fe2O4 (x = 0.8 and 0.9)) is presented in the frame of structural, dielectric, ferroelectric and magnetic properties. PZT and NZF/CF powders were synthesized by auto combustion technique. The composites were synthesized by mixing the appropriate amount of individual phases using conventional sintering. XRD data indicated the formation of well crystallized structure of PZT and NZF/CF, without the presence of undesirable phases. SEM micrographs revealed a uniform grain distribution of both, ferroelectric and ferromagnetic phases. Non-saturated hysteresis loops are evident in all samples due to the existence of nonferroelectric ferrite phase. All the samples exhibit typical ferromagnetic hysteresis loop, indicating the presence of the order magnetic structure. Dielectric investigations revealed that ferrites are the main source of charge carriers, which must be of electronic origin. The activation energy of effective electrical resistivity is heavily influenced by the ferroelectric phase.

Multiferroic composite materials based on antimony doped barium titanate/nickel ferrite were prepared by a mixing route. In order to obtain fine grained microstructure composite materials, pure constituent phases were prepared via chemical methods. The optimization of processing parameters has been made in order to reduce the chemical reactions at the interfaces between ferroelectric-ferrite phases. XRD data confirmed the presence of both barium titanate and nickel ferrite phases in the ceramic samples. The resistivity data obtained from impedance as well as calculated activation energies indicated the grain boundary contribution as a more influential effect in the total resistivity of ceramics. Dielectric permittivity enhancement in comparison with composites prepared from pure barium titanate was noticed. Well defined hysteresis loops have shown the changes of properties induced by the modification of the barium titanate phase with Sb doping and due to the co-existence of two different phases in the materials. The comparative study of magnetic properties of obtained composite materials was presented. The results on the magnetodielectric properties are understood in terms of the stress induced variations in the polarization and dielectric permittivity.

U ovoj doktorskoj disertaciji ispitivana su magneto-električna svojstva kompozitnih materijala koji se sastoje od magnetne faze, nikl-cink ferita, i feroelektrične faze, barijum titanata u razlicitim masenim odnosima. Maseni odnosi ovih faza su menjani u cilju dobijanja kompozitnog materijala dobrih magnetnih i električnih svojstava. Prahovi čistih polaznih materijala, nikl ferita i barijum titanata sintetisani su hemijskom metodom auto–sagorevanja. Ova metoda predstavlja važnu tehniku za sintezu kompozita, legura, katalizatora, itd. Danas metoda auto-sagorevanja čini veoma popularan pristup za pripremu nanomaterijala koji su našli industrijsku primenu u mnogim zemljama. Prahovi nikl ferita i nikl cink ferita su dobijeni kalcinacijom prekursora na temperaturi od 1000 °C tokom 1h dok je kalcinacija barijum titanata vršena na od 900 °C tokom 2h. Prahovi kompozita dobijeni su homogenizacijom prahova nikl ferita, nikl cink ferita sa prahom barijum titanata u izopropanolu kao medijumu za mlevenje i u planetarnom mlinu u trajanju od 24 h. Dobijeni prahovi su presovani i sinterovani na različitim temperaturama. Izvršena je optimizacija procesa sinterovanja kojom su određene temperature sinterovanja svakog kompozita pojedinačno u intervalu od 1120-1200 °C u cilju dobijanja najveće gustine keramičkih uzoraka. Karakterizacija dobijenih keramičkih kompozita vršena je različitim fizičko hemijskim metodama analize. Metodom rendgenske difrakcije praćen je fazni sastav dobijenih prahova i keramike i na osnovu XRD dijagrama određene su optimalne temperature sinterovanja. Morfologije čestica praha čistog nikl cink ferita i barijum titanata određene su na osnovu analize mikrofotografija dobijenih skenirajućom elektronskom mikroskopijom. Analizom je utvrđeno da se prah nikl cink ferita sastoji od individualnih čestica sfernog oblika, koje su malih veličina (< 200 nm). Čestice praha barijum titanata su veličine oko 100 nm, a njihov oblik čestica je takođe sferan. Analizom SEM mikrograf, In this doctoral dissertation magneto-electric properties of composite materials consisting of magnetic nickel zinc ferrite phase and ferroelectric barium titanate phase in different mass ratios were investigated. Mass ratios of these phases were differed in order to obtain composite materials with optimal magnetic and electrical properties. Powders of pure starting materials, nickel zinc ferrite and barium titanate were synthesized by the chemical auto-combustion method. This is important technique for the synthesis of composites, alloys, catalyst, etc. In the present time the auto-combustion method is becoming rather popular method for the preparation of nano materials with industrial application in many countries. Powders of nickel ferrite and nickel zinc ferrite were obtained by the calcination of precursors at the temperatures of 1000 °C with duration of 1h, while the calcination of barium titanate was conducted at 900 °C for 24h. Powders of composites were obtained by homogenization of nickel ferrite and nickel zinc ferrite powders with the powder of barium titanate in isopropanol as the milling medium and in the planetary ball mill for 24h. The obtained powders were then pressed and sintered at different temperatures. The sintering process was optimized and the particular sintering temperatures of each composite within the temperature interval of 1120-1200 °C were determined in order to obtain ceramic samples with high density. The characterization of the obtained ceramic composites was performed by different physical-chemical analytical methods. The X-ray diffraction method was used for monitoring the phase composition of obtained powders and ceramics and based on XRD patterns the optimal sintering temperatures were determined. The morphologie of the powders of pure nickel zinc ferrite and barium titanate powders were analyzed based on the analyses of the images obtained by scanning electron microscopy. It was determined that the powder of nickel zinc ferrit

Photoluminescence (PL) analysis provide us important information about the structure of materials, however the PL behavior of (x)Ni0.7Zn0.3Fe2O4-(1-x)BaTiO3 ((x)NZF-(1-x)BT) multiferroic composites is not very well know. Based on this, (x)NZF-(1-x)BT powders whit different ratio of NZF/BT (x= 0.1, 0.3, 0.5, 0.7, 0.9) were synthesized by auto-combustion method. After that, the PL property of the composites was explored through measurements carried out using as excitation source a krypton laser with wavelength of 350 nm. The presence of PL emission suggests that the structures of the materials are medium range disordered. Oxygen vacancies (anion vacancies), metal vacancies (cation vacancy) and lattice distortion are responsible by PL emission due to formation of structural defects which are essential to promote the electronic transitions inside band gap. Emission at low energy (green/yellow/red) occurs due to deep defects which modify the Fermi level generating intermediary levels near the conduction band. On the other hand, PL emission at high energy region (violet/ blue) is originated by the presence of shallow defects which generate states next to the valence band. In the present work, all samples showed a broad band emission centered around 450 nm (Figure 1), being a region characteristic of contribution of shallow defects for photoluminescence emission. In addition, the PL broad band emission is an evidence of structural disorder in the lattice of materials which promotes the formation of numerous states within the band gap.

Multiferroic composites with formula Ni0.7Zn0.3Fe2O4 - BaTiO3 (x = 0.1, 0.3, 0.5, 0.7, 0.9) were prepared by mixing chemically obtained NZF and BT powders in the planetary mill for 24 h. NiZnFe2O4 (NZF) powder was prepared by auto-combustion method starting from nickel, zinc and iron nitrates. Barium titanate (BT) powder was prepared with the same method. The optimization of sintering process was performed. One series of powders were pressed and sintered at 1170 °C, while the others were sintered at 1120 °C. X-ray measurements confirmed the presence of NZF, BT phases and the traces of barium ferrite phase. The microstructures of the ceramics show (Fig. 1.) the formation of grains with different shape and size. The formation of polygonal (NZF grains), rounded (BT grains) and plate like grains (barium ferrite phase) was noticed. The magnetic analyses showed that in the composites due to existence of ferroelectric phase a dilution effect appears.

Barium titanate (BT) is a ferroelectric material with a perovskite structure important in the field of electronics. Due to high flexiblity of its crystal lattice it has the capabilty to host ions with different oxidation state and careful selection of dopants could enable tailoring of barium titanate structure and electrical properties. Barium titanate doped with La, Sb, Sm, Nb and Mn will be presented in the light of structural changes and their influence on electrical properties modification. Doping with La, Sb and Sm in very low concentrations induces symmetry change from tatragonal to pseudo-cubic. La, Sb, Nb and Sm are proven to be grain growth inhibitors, with the different effect on obtained ceramics density. Dielectric permittivity value was significantly changed depending on dopant kind and concentration. Partial substitution of Ba or Ti ions by some of this dopants induced the movement of phase transition peaks to the lower temperatures and caused the formation of diffuse phase transition. In this way, the application of barium titanate can be widened from capacitors to PTCR sensors, gas and humidity sensors, etc. In the recent years, there is a growing interest for multiferroic materials with barium titanate as a main component. When being mixed with ferrites in the multiferroic composites the electrical properties of barium titanate are being compromised. Dielectric permittivity starts to decrease in comparison with pure BT ferroelectric material. Using of doped barium titanate as a part of the multiferroic material could enhance the overall dielectric permittivity of barium titanate and therefore the dielectric properties of the multiferroic material. Mixing route was used for the preparation of BaTiO3-NiFe2O4, BaTiO3-NiZnFe2O4, Ba(Sb)TiO3- NiFe2O4 composite materials. Magnetic and electrical properties of multiferroic materials have shown the dilution effect due to existence of both, ferroelectric and ferrite phases in the samematerial.

Conventional solid-state method was used to prepare powders of barium titanate (BT) doped with different concentration of Sm. Influence of Sm addition on the structure modification, grain growth inhibition and microstructure development was studied. Dielectric properties of doped samples were significantly modified. With doping, a diffuse kind of ferro-para phase transition was induced, phase transition positions were moved and dielectric permittivity values were lowered. On the other hand, Sm doping affected the decrease of dielectric losses. The impedance complex plane plots showed a one single semicircular arc, indicating grain contribution as a main effect on the total conduction of the doped materials. On the other hand, different electro-active regions in the modulus plane plots were distinguish. The comparison between impedance and modulus scaling behavior presented the localized movement of charge carriers. P-E hysteresis loops have shown the dilution of ferroelectric properties with Sm doping.

Ferroics and multiferroics are among the most attractive multifunctional materials. In recent years, multiferroic composite consisted of two or more ferroic orders, such as ferroelectric, ferromagnetic, or ferroelastic, in which coupling between these phases can produce magnetoelectric effect, has been drawing significant attention. Besides others, (Ni, Zn)Fe2O4-BaTiO3 composites have attracted considerable attention not only due to fundamental research of magneto-electric effect, but also for the potential applications in many electronic devices such as drug delivery, heterogeneous catalysis, levitated railway system, magnetic-refrigeration, microwave devices, antennas, memory devices, etc. In this composite, (Ni,Zn)Fe2O4(NZF) possesses magnetic behavior, and the ferroelectricity is due to the presence of BaTiO3 (BT). In the present work, it was investigated the structural and photoluminiscence properties of NZF-BT composite nanopowders prepared by auto-combution method and the different ratio of NZF/BT was explored. XRD indicated well cristallized powders but with small presence of secondary phases respecting to BT. By FE-SEM analyses was noticed the agglomerates with wide particles size distribution, as well as the difference of the particles morphology between (Ni,Zn)Fe2O4 and BaTiO3. FT-IR spectra display interactions between metal-oxygen around 500-600 cm-1. The different ratio of NZF/BT effects on the optical band gap values indicating the formation of intermediary levels modifying the Fermi level. Photoluminescence (PL) analysis provides important information about the materials structures, however the PL behavior of these composites is not very well known. The presence of PL emission suggests that the structures of the materials are medium range disordered. All samples showed a broad band emission centered around 450 nm, being a region characteristic of resultant emission from the presence of shallow defects in materials structures. This behavior is reinfor

Nickel zinc ferrite (NZF), cobalt ferrite (CF) and barium titanate (BT) nanosized powders were synthesised by auto-combustion method. Multiferroic composites with the formula xPbZr0.52Ti0.48O3+(1-x)CoFe2O4 and xPbZr0.52Ti0.48O3+(1-x)Ni0.7Zn0.3Fe2O4 (x=0.8 and 0.9) were prepared from nickel zinc ferrite, cobalt ferrite and barium titanate powders by mixing in planetary ball mill for 24 h. Pellets were sintered at different temperatures in order to obtain dense, two phased composites. XRD data indicated the formation of well crystallized structure of PZT and NZF/CF phase in the composite ceramics. SEM micrographs revealed a uniform grain distribution of both phases without any secondary phases. Magnetic measurements of all sintered composites were carried out and presented in Figure 1. All the composite samples exhibit typical ferromagnetic hysteresis loop, indicating the presence of the order magnetic structure. Saturation magnetization moment decreases with increasing PZT content, because of non-magnetic PZT phase

Multiferroic (MF) materials with simultaneous magnetic and electric long range order and occasionally, mutual magnetoelectric (ME) coupling, have recently attracted considerable interest. These compounds present opportunities for potential applications in information storage, the emerging field of spintronics, sensors, and multistate memory devices [1]. The ME phenomenon is observed in both single- phase as well as composite materials. The challenge in preparing such materials is to find equilibrium ferroelectric and magnetic structures preserving both properties close to the room temperature [2]. The individual phases (Ni0.7Zn0.3Fe2O4, CoFe2O4 and PbZr0.52Ti0.48O3) were prepared by citrate-nitrate combustion reaction method. Composites were prepared by mixing and homogenizing PZT and NZF/CF powders in a planetary ball mill in the ratio: (x) PZT + (1-x) CF/NZF (x = 0.8 and 0.9). XRD diagrams of a sintered composite confirm the presence of only two phases, ferroelectric PZT phase and ferrite phase. SEM analysis revealed a uniform grain arrangement of both phases. Similar values of saturation magnetization (Ms) for both types of composites were observed. Ms increases with increasing magnetic phase, as it was expected. Significantly higher values of coercive field (HC) can be seen in the composite with a cobalt-ferrite, which belongs to the group of hard ferrite unlike NZF which is soft ferrite and characterized by low values of coercive field. The ferroelectric properties of all ceramic composites were also studied.

Conventional solid-state method was used to prepare powders of pure and barium titanate (BT) doped with different concentration of samarium. Influence of samarium addition on the structure modification, grain growth inhibition and microstructure development was studied. Dielectric properties of doped samples were significantly modified. With doping, a diffuse kind of ferro-para phase transition was induced, phase transitions positions were shifted and dielectric permittivity values were lowered in comparison with pure barium titanate. Detailed impedance and modulus data analysis were presented. The impedance complex plane showed two semicircular arcs for pure BT and one single depressed semicircular arc for all doped ceramics. Different electro-active regions in the modulus plane plots were also distinguish. The comparison between impedance and modulus scaling behavior presented the localized movement of charge carriers in the pure barium titanate and both, short and long range relaxations in the ceramics doped with 0.05 mol% of Sm. P-E hysteresis loops have shown the dilution of ferroelectric properties with Sm doping.