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

DIELECTRIC INVESTIGATION OF BARIUM TITANATE WITH 0.5% ANTIMONY

Barium titanate (BaTiO:) is versatile electroceramic that exhibits high permittivity (e') making it desirable material for capacitor and others widespread applications. On heating, it undergoes a ferroelectric/paraelectric phase transition to the cubic polymorph at a Curie temperature Tc of 130C, at which e' passes through a maximum e'max and typically reaches values of -10000 in undoped ceramic samples. The phase transition is first order, and the peak in e' is correspondingly sharp [1]. For many years dopants have been used to modify the electrical properties of BaTiO3-based ceramics. For example, isovalent dopants are commonly used to alter Z. and the lower temperature orlhorhombic-hetragonal and rhombohedral/orthorhombic phase transition temperatures. In this way, the temperature of e 'max may pe modified and in some cases lead to diffuse phase transition-type behaviour. We prepared 0.5% Sb-dopped BaTiO3 sample. In the present study, the real (e ) and imaginary (e ") part and of dielectric permiittivity were investigated in the frequency range of 20 Hz to 1.0 MHz at temperature range of 1 20 K to 460 K. How we see, the temperature dependence of the dielectric permittivity is not typical for,barium titanate. But from Cole-Cole fit parameter relaxation time we see three phase transitions approximately ar T=207 K, 298 K and 273 K. In this study also will be presented barium titanate Sb-dopped with different concentration: O.1% and 0.3%

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

Characterization of Barium Titanate powders Prepared by polymeric Precursors Method

Barium titanate is the first ferro-electric ceramics and good candidate for variety applications due to its excellent dielectric, ferroelectric and piezoelectric properties. Barium titanate is a member of large family of compound with general formula ABO3 which is called perovskite. Barium titanate is the first discovered ferroelectric perovskite. Doping of BaTiO3 is very important for obtaining very interesting characteristic for various application. Barium titanate is normally an insulator but after doping with trivalent donor such as La it becomes semi-conductive. Synthesis method depends of the desired characteristic for the end application and it was distinguish a significant influence of used method on structure and properties of barium titanate materials. From the experimental results it can be concluded that powders of barium titanate obtained by Pechini process are nanosized. SEM observation indicates that higher percentage of La inhibits grain growth in doped barium titanate. Particle size distribution measurement pointed that the powders are highly agglomerated. Figure 2. shows particle size distribution for pure barium titanate powder. The next step in our work will be addressed to reducing the particle size by attrition milling with zironia media and these results will be presented and discussed

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

Electrical properties of barium bismuth titanate

Family of bismuth oxides was discovered more than 50 years ago by Aurivillius [1]. Recently, there has been renewed interest in the properties of the Aurivillius phases as temperature-stable ferro-piezoelectrics [2]. Several bismuth-layered crystal structures and their properties have been investigated in detail. However, a lot of aspects of the preparation and properties of barium bismuth titanate, BaBi4Ti4O15 [BBiT] remain unexplored, whereas being promising candidate for high-temperature piezoelectric applications, memory application and ferroelectric nonvolatile memories (Fe-RAM). In present work, BBiT was prepared by solid state reaction from mixture of oxide: BaO, TiO2 and Bi2O3 which was, previously, milled for 6 h. Mixture was heated at 750 oC for 4 h and after that sintered at 1130 oC for 1 h. The values of Tc, dielectric constant (ε), the loss tangent (tanδ), degree of relaxation behavior (∆T relaxor) and degree of diffuseness of the material (γ) are summarized in Table below. The degree of relaxation behavior is found to be only 15 K, which suggests the shift of Tc with frequency is not much distinct in BBiT ceramics. A modified Curie-Weiss relationship is used to study the diffuseness behavior of a ferroelectric phase transition where value of γ indicates the degree of diffuseness of BBiT material. The dielectric relaxation rate foollow the Vogel-Fulcher relation with activation energy = 0.013eV, relaxation frequency = 2.09×108 Hz, and freezing temperature = 378 oC. All this parametars indicate that BBiT is a relaxor ferroelectric