UTICAJ DOPANATA NA STRUKTURU I SVOJSTVA BARIJUM-TITANATNE KERAMIKE I FILMOVA DOBIJENIH IZ ORGANOMETALNIH KOMPLEKSA

Cilj nauke o materijalima je proučavanje uticaja strukture na svojstva materijala na različitim nivoima, elektronskom, kristalnom, mikro i makro nivou. Određivanje funkcionalne zavisnosti između sinteze, strukture i funkcionalnih svojstava materijala kao i izbor polaznih sirovina i tehnološkog procesa je veoma bitno, a njihovim definisanjem mogu se dobiti novi materijali sa unapred zadatim svojstvima koji mogu da nađu odgovarajuću primenu u složenim proizvodnim sistemima. Savremena nauka o materijalima uticala je i na intenzivan razvoj novih materijala u oblasti mikroelektronike. U okviru ovih materijala od posebnog interesa je elektronska keramika gde je barijum-titanatnoj keramici dato posebno mesto. Barijum titanat je feroelektrični materijal perovskitne strukture koji je već preko 60 godina od praktičnog interesa zbog svojih specifičnih električnih svojstava. Značaj ovog materijala je pre svega zasnovan na mogućnosti njegove široke primene kao kondenzatora, PTCR termistora, piezoelektričnih uređaja, optoelektronskih komponenata, u različitim vrstama senzora, mikrotalasnim filterima, itd. Veliki broj teorijskih i eksperimentalnih istraživanja je usmeren na proučavanje sinteze i karakterizacije barijum-titanatne keramike i rezultovale su dobijanjem novih materijala za najrazličitiju primenu u elektronici. Veći broj ovih primena se oslanja na mogućnost promene izolatorskih svojstava čistog barijum titanata u poluprovodnička, dodavanjem različitih vrsta dopanata. Poznato je da ugradnja jona dopanta na mesto barijuma ili titana u rešetki barijum titanata dovodi do, kako strukturnih, tako i mikrostrukturnih promena (veličina zrna, gustina) što dalje bitno utiče na promenu električnih svojstava ovog materijala. Da bi se dobila zahtevana električna svojstva neophodno je posebnu pažnju usmeriti na praćenje međuzavisnosti parametara sinteze, odnosno tehnologije i dobijene strukture, čime se može utvrditi i njihova uska povezanost sa krajnjim svojstvima dobijenog materijala. Ova doktorska teza osmišljena je i realizovana sa ciljem da se razjasni uticaj lantana i antimona kao donorskih dopanata na strukturu, mikrostrukturu i električna svojstva prahova, keramike i debelih filmova barijum titanata. Naime, barijum titanat je dopiran različitim koncentracijama lantana i antimona pri čemu su praćena svojstva dobijenih materijala. Utvrđeno je da električna svojstva barijum titanata zavise ne samo od vrste već i od koncentracije dodatog dopanta što može proširiti primenu ovog materijala u elektronici

Aurivillius BaBi4Ti4O15 based compounds: Structure, synthesis and properties

The discovery of some Aurivillius materials with high Curie temperature or fatigue-free character suggests possible applications in high temperature piezoelectric devices or non-volatile ferroelectric random access memories. Furthermore, increasing concerns for environmental issues have promoted the study of new lead-free piezoelectric materials. Barium bismuth titanate (BaBi4Ti4O15), an Aurivillius compound, is promising candidate to replace lead-based materials, both as lead-free ferroelectric and high temperature piezoelectric. In this review paper, we report a detailed overview of crystal structure, different synthesis methods and characteristic properties of barium bismuth titanate ferroelectric materials

INFLUENCE OF DOPANTS ON BARIUM BISMUTH TITANATE ELECTRICAL PROPERTIES

The Aurivillius structure has capability to host ions of different size, so a large number of different dopants can be accommodated in the BaBi4Ti4O15 (BBT) lattice. It was detected that various substitutions of Bi3+ and Ti4+ ions can affect the change of microstructure and electrical properties of barium bismuth titanate ceramics. Doping of BBT ceramics is very important due to possibility to obtain materials with required characteristics. In this work, pure and niobium and lanthanum doped barium bismuth titanate powders were prepared by conventional solid state method, according to formulas BaBi4-xLaxTi4O15 and BaBi4Ti4-5/4xNbxO15 (x=0.05). Obtained powders were uniaxially pressed and sintered at different temperature depending on the composition. The influence of dopant type on structure change, grain size reduction and microstructure development was analyzed. XRD measurements showed formation of orthorhombic BBT crystal structure without presence of secondary phase in doped samples. Dopants had influence on shifting of temperature phase transition peaks to the lower temperatures, broadening of ε - T curves and increasing relaxor behavior of phase transition. Temperature dependence of the electrical conductivity pointed out that niobium as a donor dopant decrease conductivity and lanthanum as a isovalent dopant increase conductivity of BBT ceramics. Obtained results were analyzed in the frame of the influence of the grain and grain boundaries contribution to the dielectric behavior through impedance spectroscopy

DIELECTRIC INVESTIGATIONS OF BARIUM TITANATE DOPED WITH DEFERENT CONCENTRATION OF LANTHANUM OR ANTIMONY

The dielectric properties of barium titanate doped with different concentration lanthanum or antimony are investigated. There are samples with 0.3 mol%, 0.5 mol% lanthanum and 0.1 mol%, 0.5 mol% antimony concentrations. All samples were prepared by Pechini procedure. Dielectric measurements in the temperature range of 170 K to 420 K and frequency range of I kHz to I MHz show three phase transitions, which temperatures matches those of bulk barium titanate. Curie temperature shifts to the lower temperatufe when lanthanum or antimony concentration grows. At low frequencies, the samples present conductivity Conduction-free loss spectra are calculated using a compact solution of the Kramers-Kronig transformation and an approximation based

INFRARED SPECTROSCOPY OF UNDOPED AND LA AND Sb DOPED BaTiO3 PREPARED BY POLYMERIC PRECURSORS METHOD

The infrared spectra of ABO3 perovskites have been studied extensively. Factor group analysis for BaTiO3 with cubic symmetry (space group Pm3m : O6r) predicts only infrared bands (three triply degenerate infrared active modes of F1o symmetry) and one optically silent (neither infrared nor Raman active) mode of F2u symmetry. The three infrared active modes are commonly called the stretching modes (B-O bond-length modulation), and the external mode in which the 8Oo octahedron vibrates against the I atoms. In tetragonal symmetry (space group P4mm : C4v), 12 fundamental optical modes with the following irreducible representation are expected: 3Ab 4E and Br [2,3]. The perovskite structure has capability to host ions of different size, so a large number of different dopants can be accommodated in the BaTiO3 lattice that makes BaTiO3 semiconductive. Doping of BT ceramics is very important for obtaining very interesting characteristics for potential applications. The aim of this study is to investigate the influence of La- and Sb- doping on the BaTiO3 synthesized through the Pechini method. Infrared spectroscopy was used in addition to the XRD, Raman spectroscopy and SEM investigations in order to find evidence of the structural phase in undoped and doped BaTiO: ceramics' BaTiO3 powders were prepared by the polymeric organometallic precursors method (Pechini process) using barium and titanium citrates and for doping were used lanthanum nitrate and antimony acetate. The powders were isostatically pressed into pellets 8 mm in diameter and average thickness of about 2.5 mm at pressure of 98.1 MPa. Sintering was performed at 1300'C for 8 h and the heating rate was 10 oC/min with nature cooling in an air atmosphere. Far-infrared reflectivity measurements were made in spectral range (50-700 cm-1; at room temperature with BOMEM DA8 spectrometer. Figure 1 show the IR spectrum of the BaTiO3 and La- and Sb-doped BaTiO3 ceramics sintered at 1300C for 8 h. The bands in the lower wave number range (50-700 cm-1) are due to Ti-O vibrations. The characteristic peak is found for all samples. The modes at 180 and 470 cm-r belong to the At representation to which the soft phonon mode associated with the ferroelectric phase transition at Tc - 395 K belongs. The broad band over 50-180 cm-' is due to soft phonon. Because of the over damped character of the soft phonon, it is difficult to determine the frequency. The intensity of three peaks of the doped BT 0.5 mol% Sb, undoped barium titanate and BT doped 0.5 mol % La appear on 183, 184 and 185 cm-1, respectively, intensities of the mode's at 180, 250 and 470 cm-t decrease for BaTio3 and La- and Sb-doped BaTiO3:, respectively. The modes at 382' 439 and 612 cm-t can be observed in case Sb- doped BaTiO3. This suggests a change of crystal structure. These results are in agreement with our previous investigations [4]. All observations related to IR indicate the formation of pure single phase of BT and La and Sb doped BT

Influence of dopants on barium bismuth titanate electrical properties

The Aurivillius structure has capability to host ions of different size, so a large number of different dopants can be accommodated in the BaBi4Ti4O15 (BBT) lattice. It was detected that various substitutions of Bi3+ and Ti4+ ions can affect the change of microstructure and electrical properties of barium bismuth titanate ceramics. Doping of BBT ceramics is very important due to possibility to obtain materials with required characteristics [1]. In this work, pure and niobium and lanthanum doped barium bismuth titanate powders were prepared by conventional solid state method, according to formulas BaBi4-xLaxTi4O15 and BaBi4Ti4-5/4xNbxO15 (x=0.05). Obtained powders were uniaxially pressed and sintered at different temperature depending on the composition. The influence of dopant type on structure change, grain size reduction and microstructure development was analyzed. XRD measurements showed formation of orthorhombic BBT crystal structure without presence of secondary phase in doped samples. Dopants had influence on shifting of temperature phase transition peaks to the lower temperatures, broadening of ε - T curves and increasing relaxor behavior of phase transition (Table). Temperature dependence of the electrical conductivity shown at Fig. pointed out that niobium as a donor dopant decrease conductivity [2] and lanthanum as a isovalent dopant increase conductivity of BBT ceramics. Obtained results were analyzed in the frame of the influence of the grain and grain boundaries contribution to the dielectric behavior through impedance spectroscopy

Sintering heating and cooling rates as a method of modifying electrical properties of BiFeO3 ceramics

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

MICROSTRUCTURE DEVELOPMENT OF Bi4Ti3O12 AND BaBi4Ti4O15 CERAMICS PREPARED BY MECHANOCHEMICAL SYNTHESIS

Scveral bismuth-layered crystal structure and their properties have been investigated- in detail. However, a lot of aspects of the preparation and properties of barium bismuth titanate unexplored, whereas being promising candidate for memory applications. In present work barium-bismuth titanate (BaBi4Ti4O15-BBT) was prepared from stoichiometric, quantities of barium titanate and bisrnuth titanate obtained via mechanochemical synthesis. Barium titanate (BaTi3O12:-BT) has been synthesised from michture of BaO and Tio2 and bismuth titanate (Bi4Ti3O12-BIT) was prepared starting frorn Bi2O3 and TiO2 commercially available. Mechanochemical synthesis was performed in air atmosphere in , planetary ball mill, for BT during 60 min and for BIT during 360 min. Milling condition were: zirconium oxide jars and zirconium oxide balls, ball-to-powder weight ration 20:1 and determined basic disc and disc with jars rotation speed. The powder mixture of BT and BIT was homogenized for 30 min and after that sintered at 1100"C for 4h. Separatly, BIT was sintered at 1000 C for 12h, in both cases without pre-calcination step and by conventional sintering technique. The Fig. I. shows the phase formation and crystal structure of BIT, BT and mixture of this powders. Pattern of BBT powder sintered at 1100.c for 4h was analysed by XRD analysis revealing the existence of tetragonal phase (Fig. 2.). The morphology of obtained powders was examined by SEM and TEM method (Fig. 3. and Fig. 4.). It can be conclude that pattern of BIT consists of nanoparticles which size is less than 20 nm. Mixture of BIT and BT consists of agglomerates of varying size and morphology which size is about 250 nm. The microstructure development of BIT and BBT ceramics was followed by SEM. From Fig 5. and Fig. 6. it can be observed that BIT consists of plate-like grains but in the case of BBT beside plate-like grains exist and spheric grains, also' It is evident addition leads to the change in the microstructure development

Ferroelectric behavior of pure and La doped barium bismuth-titanate ceramics

Baruim bismuth titanate (BaBi4Ti4O15-BBiT) is a member of the Aurivillius bismuth-based layer-structure perovskites. The BBT grains possess plate-like shape with larger surfaces parallel to the (Bi2O2)2+ layers. Their intrinsic electrical properties are anisotropic, with the maximum value of conductivity and the major component of spontaneous polarization parallel to the (Bi2O2)2+ layers. As a result, properties of the polycrystalline materials are strongly affected by their microstructure, especially by the orientation of the plate-like grains and by the length-to-thickness ratio of the grains [1]. The disadvantage of BBiT materials for high-temperature piezoelectric application is their relatively high conductivity [2]. The aim of our investigation is to find out how lanthanum (La3+) as dopant influence on electrical properties and microstructure in BBiT ceramics. BBT powders, pure and doped with 0.05, 0.15 and 0.30 mol of lanthanum, were prepared through conventional solid state reaction. BBT ceramics were obtained by sintering at temperatures ranging from 1130 °C to 1150 °C for 1h depending on the composition. On BaBi4-xLaxTi4O15 (BBLT) ceramics (x=0, 0.05, 0.15, 0.30 mol) were measured permittivity from 20 Hz to 1 MHz in wide range of temperatures (32 °C–750 °C). Obtained results were analyzed in the frame of the influence of the grain and grain boundaries contribution to the dielectric behavior through impedance spectroscopy. The temperature dependence of dielectric constant at 100 kHz for pure and La doped BBiT ceramics is showed on figure below. It is indicated that the temperature of dielectric constant maximum (Tm) of BBLT specimens significantly decreases with the increase of lanthanum content. The changes of Tm are attributed to the changes of crystal structure for BBLT specimens, which indicated that the La3+ have entered into the lattice of BBT

INFLUENCE OF FERRITES PHASE ON PROPERTIES OF THE BARIUM ZIRCONIUM TITANATE BASED MULTIFERROIC COMPOSITES

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