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Multiferroic composites with general formula Ba(Ti0.95Zr0.05)O3 – Ni0.7Zn0.3Fe2O4, Ba(Ti0.95Zr0.05)O3 – CoFe2O4, Ba(Ti0.95Zr0.05)O3 – 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 °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.

Made available in DSpace on 2020-12-12T01:07:42Z (GMT). No. of bitstreams: 0 Previous issue date: 2019-12-01 The preparation and properties of thick flexible three-phase composite films based on lead zirconium titanate (PZT) and various ferrites (nickel zinc ferrite (NZF) and cobalt ferrite (CF)) were reported in this study. Properties of three-phase composite films were compared with pure polyvinylidene fluoride (PVDF) and PZT–PVDF films. X-ray diffraction data indicated the formation of well crystallized structure of PZT and NZF/CF phases, without the presence of undesirable phases. Scanning electron micrographs showed that the ceramic particles were dispersed homogeneously in the PVDF matrix and atomic force microscopy confirmed that the size of the particles is around 30 nm. Non-saturated hysteresis loops were evident in all samples due to the presence of highly conductive ferrite phases. Under magnetic field of 10 kOe, composite films exhibited a typical ferromagnetic response. Dielectric properties were investigated in the temperature range from −128 to 250 °C and frequency range of 400 Hz–1 MHz. The results showed that the value of dielectric constant of the PVDF/PZT/ferrite composites increased about 25% above the one obtained for pure PVDF. Institute for Multidisciplinary Research Belgrade University, Kneza Viseslava 1 Universidade Federal de Goiás – UFG Instituto de Química, Av Esperança s/n Faculty of Physics Vilnius University, Sauletekio al. 9 Institute Jozef Stefan, Jamova cesta 39 Instituto de Quimica-UNESP Instituto de Quimica-UNESP

Samples of homogeneous (x = 0, 0.1, and 0.2) and multilayer ceramics based on solid solutions of nickel–zinc ferrites (Ni1 – xZnx)Fe2O4 with a “contrary” composition gradient (x = 0.2 → 0 → 0.2) have been prepared by the thick-film technology. The use of the two-step sintering mode enables the ceramics synthesis and the conservation of the regular–inhomogeneous distribution of chemical elements over the thickness of the gradient samples. The microstructures and the crystal structures of the materials have been studied. The unit cell volume is shown to increase with the zinc content and, in this case, the grain size is changed only slightly. The features of the magnetization of the multilayer structures are studied for two variants of applying an external magnetic field: parallel and perpendicular to the sample plane. The resulting hysteresis loop of the multilayer gradient sample can be obtained by the “summation” of the loops of homogeneous layers of the structure. No internal fields leading to the shift and the distortion of magnetic hysteresis loops have been observed.

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 H2 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.

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.

Comparative study of different PZT-based composite materials ((x)PbZr 0.52 Ti 0.48 O 3 + (1-x)CoFe 2 O 4 and (x)PbZr 0.52 Ti 0.48 O 3 +(1-x)Ni 0.7 Zn 0.3 Fe 2 O 4 (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 non-ferroelectric 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.

Di-phase ceramic composites, with general formula xNi 0.7 Zn 0.3 Fe 2 O 4 – (1-x)BaTiO 3 (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.

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 α-phase into electro-active β and γ 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 ~ 80 μW of output voltage and power.

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.

The effect of tungsten (W 6+ ) doping on modification of the structure, dielectric, ferroelectric and electrical properties of BaBi 4 Ti 4-x W x O 15 (BBTWx, x = 0, 0.03, 0.05 and 0.07) was investigated. The ceramic samples were synthesized by the conventional solid state reaction method. XRD data indicated the formation of single-phase layered crystalline structure that confirmed orthorhombic structure type of all compositions with space group A2 1 am . SEM micrographs suggest that the grain size slightly decreases with W doping. The temperature dependent dielectric study revealed that the dielectric constant decreases with W doping while transition temperature slightly increases. Influence of tungsten on relaxor behavior and diffuseness of phase transition is also discussed. Effect of W doping on the dielectric and electrical properties were investigated in terms of ion doping and defect mechanism. The ferroelectric properties were studied by P-E hysteresis loop and it was observed that the remanent polarization increases with a small level of W doping.

Made available in DSpace on 2018-12-11T17:31:22Z (GMT). No. of bitstreams: 0 Previous issue date: 2015-12-01 Ministarstvo Prosvete, Nauke i Tehnološkog Razvoja Nickel zinc ferrite (NZF) and barium titanate (BT) were prepared by auto-combustion synthesis as an effective, simple and rapid method. Multiferroic composites with the general formula yNi1−xZnxFe2O4−(1−y)BT (x=0.3, 0.5, 0.7, y=0.5) were prepared by mixing NZF and BT powders in a liquid medium in the ball mill. The FEG micrographs indicated the primary particle size less than 100 nm for both, barium titanate and nickel zinc ferrite phases. X-ray analysis and Raman spectroscopy indicated the formation of well crystallized structure of NZF and BT phase in the composite powders and ceramics, with a small contribution of the secondary phase. The homogenous phase distribution in obtained composites was also confirmed. Impedance spectroscopy measurements were carried out in order to investigate the electrical resistivity of materials, showing that grain boundaries have greater impact on the total resistivity than grains. Saturation magnetization and remnant magnetization continuously decrease with barium titanate phase increase. Institute for Multidisciplinary Research University of Belgrade Institute of Physics University of Belgrade UNESP Faculty for Engineering UNESP Institute for Chemistry UNESP Faculty for Engineering UNESP Institute for Chemistry Ministarstvo Prosvete, Nauke i Tehnološkog Razvoja: III 45021

Aurivillius Bi5Ti3FeO15 (BTF) and Bi5−xLaxTi3FeO15 (BLTF) ceramics were successfully synthesized by a simple solid state reaction method. The samples were characterized by X-ray diffraction with no impurity phase identified. SEM micrographs show an evident decrease of grain size of La modified ceramics in comparison with pure BTF. Dielectric properties were investigated in a wide range of temperatures (300–1000 K) and frequencies (1 Hz–1 MHz). The Curie temperature was found to decrease in BLTF when compared to BTF ceramics. An energy bandgap of 1.83 and 1.77 eV for the BTF and BLTF ceramics, respectively was determined from UV–Vis diffuse absorption spectrum. Influence of La doping on ferroelectric and ferromagnetic measurements of both samples was also performed. Very weak ferromagnetism inside BTF can be observed while samples with La content showed complete paramagnetic behavior.

Modified Pechini process was used to prepare nanopowders of barium titanate (BT) co-doped with different concentrations of niobium and manganese. Influence of dopants on the grain growth inhibition and microstructure development was analyzed. The addition of dopants significantly influenced the dielectric properties modification. The obtained ɛ–T curves of all ceramics have the shape of typical ferroelectric material but the increase of dielectric permittivity value and movement of phase transitions with different dopant concentrations were clearly noticed. Grain and grain boundary resistivities for all co-doped ceramics were extracted from detailed impedance analysis and the grain boundary effect was indicated as a dominant effect in the total conduction of the materials. The well-defined and saturated P–E hysteresis loops of the ceramics confirmed the existence of ferroelectric properties.

A broadband dielectric investigation and Mossbauer studies were performed on 0.7BaTiO3–0.3NiFe2O4 composite ceramics prepared from chemically obtained barium titanate and nickel ferrite powders. Dielectric spectroscopy revealed a Debye-type relaxation at frequencies between 10 GHz and 1 THz. The relaxation time slows down on cooling according to the Arrhenius law which can be attributed to the transformation of the system from the paraelectric to the ferroelectric phase through an intermediate relaxor state. The temperature dependence of the center shift of the Mossbauer spectrum was analyzed by applying Debye and Einstein models. Its deviation from these models can be attributed to the anharmonicity. It is also possible that the center shift is affected by the Fe atoms incorporated in BaTiO3 lattice or at the interfaces between BaTiO3 and NiFe2O4.

Barium titanate nanopowders doped with various concentrations of antimony were synthesized by polymeric precursors method based on modified Pechini process. Obtained powders were pressed and sintered at 1,573 K for 8 h. The temperature dependence of dielectric permittivity pointed on the significant influence of added antimony on dielectric properties of obtained materials. The analysis of impedance spectrum in the temperature range 250–445 K has shown the presence of one semicircle that corresponds to the grain contribution but impedance spectrum at 773 K showed possible overlapping of two semicircles indicating also grain boundary resistivity. The total specific resistivity obtained from impedance analysis showed modest PTCR jump in the heavily doped barium titanate ceramics. The electric field dependence of permittivity of the ceramics was investigated in detail. The experimental data were analyzed using Johnson model.

Nanosized nickel zinc ferrite powders with general formula Ni1−xZnxFe2O4 (x=0.0, 0.3, 0.5, 0.7, 1.0) were synthesized by an auto-combustion method starting from metal nitrates. X-ray analysis indicated the formation of well crystallized Ni–Zn ferrite phases, and Raman spectroscopy enabled a precise phases identification. The change of the grain size and density with increasing Zn content was confirmed by scanning electron microscopy. Magnetization of saturation and remnant magnetization, both, continuously increase up to x=0.3 of Zn, and then decrease for more Zn. The influence of the grain size of investigated systems on the saturation magnetization was studied. Impedance spectroscopy measurements were carried out in order to investigate the electrical resistivity of materials, showing that grain boundaries have greater impact on total resistivity that grains.

The processing of ferroelectric BaBi 4 Ti 4 O 15 (BBT) ceramics from powders prepared by conventional solid state reaction (SSR) and mechanochemical activation (MA) has been investigated. It was shown that MA synthesis reduces the synthesis temperature of BBT powders, leading to smaller particles with reduced anisotropy and consequently to smaller grain size of ceramics. Dielectric properties were investigated in a wide range of temperatures (20–800 °C) and frequencies (1.21 kHz to 1 MHz). The relative dielectric permittivity at Curie temperature was higher for solid state obtained ceramics than for the mechanically treated ones. The conductivity of sintered samples was studied, suggesting decreasing of conductivity of BBT-MA in comparison with BBT-SS ceramics. The influence of the grain and the grain boundaries contribution to the dielectric behavior in both ceramics was analyzed through impedance spectroscopy. A well-defined ferroelectric hysteresis loop was obtained for both samples.

Multiferroic composites with the general formula x BaTiO 3 –(1− x ) NiFe 2 O 4 ( x =0.5, 0.7, 0.8) were prepared by mixing chemically obtained nickel ferrite and barium titanate powders. Optimum processing parameters for a reduction of chemical reactions at the interfaces between ferroelectric-ferrite phases were found. The presence of the nickel ferrite and barium titanate single phases was detected by X-ray measurements. Good quality of the homogenized ceramics containing both phases was confirmed by use of scanning electron microscopy. Dielectric measurements showed the superposition of the multiple conductivity mechanisms responsible for the dielectric dispersion at frequencies up to 1 MHz. Calculated activation energies for DC conductivity showed the contribution of oxygen vacancies and Maxwell-Wagner related phenomena. Magnetic measurements of the composite materials were performed showing the coercivity increase and saturation of the magnetization moment decrease with the increase of barium titanate content.

Antimony doped barium titanate powders were synthesized by polymeric precursors method based on modified Pechini process. Obtained powders were pressed and sintered at 1300 °C for 8 h. XRD analysis showed the formation of tetragonal crystal structure in barium titanate ceramics. The decrease of tetragonality was noticed with antimony concentration increase. The influence of antimony concentration on structure change, grain size reduction and microstructure development was analyzed. Dielectric behavior of pure and antimony doped ceramics showed the change from classical to diffuse ferroelectric material. A modified Curie–Weiss law was used to explore the connection between doping level and the degree of diffuseness of phase transition. The analysis of impedance at higher temperatures showed the presence of both grain interior and grain boundary effects. Modest PTCR jump was observed in the doped barium titanate ceramics.

Pure and lanthanum doped barium bismuth titanate BaBi 4− x La x Ti 4 O 15 (BBLT, x =0, 0.05, 0.15, 0.30) ceramics were prepared utilizing solid state method. The X-ray diffraction (XRD) data confirmed formation of single-phase Aurivillius compounds while SEM micrographs did not show evident grain size change of doped ceramics. Dielectric properties were investigated in 1.21 kHz to 1 MHz frequency range and in the temperature range of 20 to 727 °C. When Bi 3+ is substituted with La 3+ , a significant disorder was induced and the material exhibited broadening of the phase transition. Impedance analysis confirmed the presence of two semicircular arcs in doped samples suggesting the existence of grain and grain-boundary conduction. The dc-conductivity and activation energies were evaluated for all compositions.

Barium titanate ceramics doped with 0.3 mol.% lanthanum and co-doped with 0.3 mol.% lanthanum and 0.05 mol.% manganese were investigated. The powders were prepared by a modi ed polymeric precursor method based on the Pechini process. The ceramics were obtained by sintering at 1300 ◦C for 8 h. The in uence of dopants on structural changes and grain size reduction was analyzed. The presence of dopants in uenced the tetragonality of the barium titanate crystal structure. Reduction of polygonal grain size with dopant addition was noticed. In the doped ceramics, characteristic phase transitions were shifted to lower temperatures in comparison with pure barium titanate. The dielectric permittivity value showed the tendency of a slight increase with lanthanum addition and further increase with adding of manganese. La as a single dopant increased the di useness of phase transitions indicating the formation of a di use ferroelectric material but in the co-doped ceramics the phase transition di useness decreased. The resistivity of the co-doped ceramics was higher than for lanthanum doped ceramics, indicating possible segregation of manganese at grain boundaries that in uenced the total resistivity of the material.

Barium titanate ceramics were prepared using the nanopowder resulting from a polymeric precursor method, a type of modified Pechini process. The obtained nanopowder was observed to agglomerate and in order to de-agglomerate the powder and enhance the properties of the barium titanate the material was attrition milled. The impact of this attrition milling on the electrical properties of the barium titanate was analysed. The temperature dependence of the relative dielectric permittivity showed three structural phase transitions that are characteristic for ferroelectric barium titanate ceramics. The relative dielectric permittivity at the Curie temperature was higher for the attrition-treated sample than for the non-treated barium titanate. The dielectric losses were below 0.04 in both barium titanate ceramics. The grain and grain-boundary contributions to the total resistivity were observed using impedance analyses for both ceramics. A well-defined ferroelectric hysteresis loop and piezoelectric coefficient d33 = 150 pC/N were obtained for the ceramics prepared from the de-agglomerated powder. In this way we were able to demonstrate that by attrition milling of chemically obtained powders the ferroelectric and piezoelectric properties of the ceramics could be enhanced.

Barium titanate powder was prepared by soft chemical process from polymeric precursors (modified Pechini process). The synthesized barium titanate (BT) powder was nanosized and the factor of agglomeration ( F agg ) pointed the existence of agglomerates. In order to de-agglomerate nanopowder and to enhance BT properties the attrition milling was performed. The milled powder (BTA) possessed smaller particles and the size and number of agglomerates was significantly reduced. To investigate the effect of milling on improvement of ceramics electrical properties, both BT and BTA powders were uniaxially pressed and sintered at 1300 °C for 8 h in air. The temperature dependence of relative permittivity showed three structural phase transitions for ferroelectric barium titanate ceramics. The dielectric constant at Curie temperature was ∼6700 for BTA which is much higher than 1340, obtained for non-treated BT. The dielectric losses were below 0.04 in both BT ceramics. At higher temperatures the analysis of impedance measurements showed the presence of both grain interior and grain boundary effects. Much higher grain and grain boundary resistivities were obtained for the BTA ceramics.

BaBi4Ti4–5/4xNbxO15 (BBNTx, x = 0, 0.05, 0.15, 0.30) ceramics have been prepared by solid state method. XRD data indicate the formation of single-phase-layered perovskites for all compositions. SEM micrographs suggest that the grain size decreases with Nb doping. The effect of niobium doping on the dielectric and relaxor behavior of BaBi4Ti4O15 ceramics was investigated in a wide range of temperatures (20–777 °C) and frequencies (1.21 kHz to 1 MHz). Nb doping influences Tc decrease as well as the decrease of dielectric permittivity at Curie temperature. At room temperature, undoped BaBi4Ti4O15 exhibits dielectric constant of ∼204 at 100 kHz, that slightly increases with Nb doping. The conductivity of BBNT5 ceramics is found to be lower than that of other investigated compositions. The value of activation energy of σDC was found to be 0.89 eV, 1.01 eV, 0.93 eV and 0.71 eV for BBT, BBNT5, BBNT15 and BBNT30, respectively.

Pure and lanthanum doped barium titanate (BT) ceramics were prepared by sintering pellets at 1300 °C for 8 h, obtained from nanopowders synthesized by the polymeric precursor method. XRD results showed formation of a tetragonal structure. The presence of dopants changed the tetragonal structure to pseudo-cubic. The polygonal grain size was reduced up to 300 nm with addition of lanthanum as a donor dopant. Determined dielectric properties revealed that lanthanum modified BT ceramics possessed a diffused ferroelectric character in comparison with pure BT that is a classical ferroelectric material. In doped BT phase transition temperatures were shifted to lower temperatures and dielectric constant values were much higher than in pure BT. A modified Currie Weiss law was used to explore the connection between the doping level and degree of diffuseness of phase transitions. Impedance spectroscopy measurements were carried out at different temperatures in order to investigate electrical resistivity of materials and appearance of a PTCR effect.

Nanopowders of pure and antimony doped barium titanate (BaTiO3-BT) were synthesized by polymeric precursors method based on Pechini process. Obtained powders were pressed and sintered at 1300 °C for 8 h. XRD analysis showed the formation of cubic crystal structure in all nanopowders and tetragonal in BT ceramics. The influence of antimony concentration on structure change, grain size reduction and microstructure development was analyzed. Dielectric behavior of pure and antimony doped ceramics was studied as a function of temperature and frequency. The significant dielectric properties modification as a consequence of doping with different antimony concentration was noticed. The electrical resistivity measurements pointed out that antimony concentration influenced also on materials change from insulator to semiconductor.

The samples of homogeneous (x = 0; 0.1; 0.2) and multilayer ceramics with “oncoming” compositional gradient (x = 0.2→0→0.2) based on solid solutions of nickel – zinc ferrites (Ni1–xZnx) Fe2O4 have been prepared by thick-film technology. It was possible to ensure the synthesis of ceramics and to maintain inhomogeneous distribution of chemical elements throughout the thickness of the graded samples using the two-stage mode of heat treatment. Microstructure and crystal structure of the materials are studied. It is shown that the volume of the unit cell increases with increasing zinc content, while the grain size does not change significantly. The features of the magnetization of multilayer structures were investigated for two variants of application of external magnetic field (parallel and perpendicular to the sample plane). The resulting hysteresis loop for multilayer graded sample can be obtained by “summing up” the loops of homogeneous layers of the structure. No internal fields leading to a shift and distortion of the magnetic hysteresis loops were detected.