The influence of synthesis parameters and dopants on structure and properties of barium bismuth-titanate ceramics

U okviru ove doktorske disertacije proučavan je uticaj uslova sinteze tj. mehaničke aktivacije na formiranje strukture barijum bizmut-titanata, kao i na svojstva dobijene keramike. Detaljno i sistematski je proučavan uticaj La3+ kao izovalentnog dopanta i Nb5+ kao donorskog dopanta na dielektrična i električna svojstva barijum bizmut-titanatne keramike. Smeša prahova BaO, TiO2 i Bi2O3 u ekvivalentnom odnosu je mehanički aktivirana u planetarnom mlinu u toku 0 - 6 h. Dinamika formiranja novih faza praćena je metodom rendgenske difrakcije. Utvrđeno je da nakon 6 h mlevenja dolazi do formiranja slojevite Aurivilijusove strukture. Termičkim tretmanom na 850 oC tokom 1 h od mehanički aktivirane smeše oksida tokom 6 h, sintetisan je BaBi4Ti4O15. Konvencionalnim postupkom reakcije u čvrstom stanju dobijeni su prahovi čistog i dopiranog barijum bizmut-titanata. Formiranje odgovarajuće strukture u prahovima koji su dobijeni ovim postupkom praćeno je metodom rendgenske difrakcije, tako da je utvrđen mehanizam formiranja barijum bizmut-titanata. Temperatura na kojoj se formira čista faza barijum bizmut-titanta je 950 oC nakon 1 h sinterovanja. Laserskim difraktometrom određena je prosečna veličina čestica prahova dobijenih konvencionalnim postupkom sinteze i praha koji je prethodno mehaniči aktiviran. Na osnovu ovih rezultata i rezultata skenirajuće elektronske mikroskopije uočen je bitan uticaj mehaničke aktivacije na smanjenje veličine čestica aktiviranog praha, što dovodi do povećanja njegove reaktivnosti. Jednoosnim presovanjem i izotermskim sinterovanjem prahova na temperaturama 1120 - 1150 oC (u zavisnosti od sastava) dobijeni su keramički uzorci čistog i dopiranih uzorka barijum bizmut-titanata. Električna svojstva dobijenih materijala merena su u opsegu temperatura od 27 do 727 °C i oblasti frekvencija od 1,21 kHz do 1 MHz u atmosferi vazduha. Rezultati dielektričnih merenja ukazuju na bitne promene vrednosti dielektrične permitivnosti sa dodatkom dopanata. Uočeno je pomeranje temperature faznog prelaza (iz polarne u nepolarnu fazu) ka nižim vrednostima, širenje pikova, kao i povećanje stepena relaksacije faznog prelaza usled inkorporacije jona u kristalnu strukturu jedinjenja. Potvrđeno je da mehanička aktivacija utiče na smanjenje veličine zrna, pa samim tim i na promenu vrednosti dielektrične permitivnosti na Kiri temperaturi. Korišćenjem modifikovanog Kiri-Vajs zakona uočeno je da mehanička aktivacija utiče na povećanje stepena difuzivnosti dok je, korišćenjem Vogel-Fučerove zavisnosti, potvrđeno smanjenje stepena relaksacije faznog prelaza...In this doctoral dissertation the influence of synthesis conditions, i.e. mechanical activation on the structure formation and properties of barium bismuth titanate ceramics was studied. The influence of La3+, as an isovalent dopant and Nb5+, as a donor dopant on the dielectric and electrical properties on this type of ceramics was also systematically studied. An equimolar BaO, TiO2 and Bi2O3 powder mixture was mechanically activated in a planetary mill for 0 - 6 h. The dynamics of new phases formation was monitored by X-ray diffraction. It was found that 6 h of milling leads to the formation of layered Aurivillius structure. Oxide mixtures mechanically activated for 6 h was heat treated at 850 °C for 1 h when BaBi4Ti4O15 was formed. Powders of pure and doped barium bismuth titanate were obtained by conventional solid state reaction method. Determination of appropriate structures in powders obtained by this procedure was followed by X-ray diffraction. The mechanism of the formation of barium bismuth titanate was established. The temperature at which it forms a pure phase was specified to be 950 °C after 1 h of sintering. The average particle size of powders obtained by conventional method and mechanical activated powder was determing using laser diffraction measurement. Based on these results and the results of scanning electron microscopy a significant influence of mechanical activation on the reduction of pawder particle size was noticed, leading to an increase of reactivity. Using uniaxial press and isothermal sintering at temperatures of 1120-1150 oC (depending on the composition) ceramic samples of pure and doped barium bismuth titanate were obtained. Electrical measurements of the obtained materials were performed in the temperature range from 27 to 727 °C and the frequency range of 1.21 kHz to 1 MHz, in air atmosphere. The results of dielectric measurements indicate a significant change in the dielectric constant value with the addition of dopants. Phase transition temperature shift and broadening of peaks were noticed as well as the increase of the degree of phase transition relaxation due to the incorporation of ions in the crystal structure of compounds. Exploring the influence of mechanical activation, it was confirmed that the mechanical activation effects the reduction of grain size and thus the change of dielectric constant value at the Curie temperature. Using a modified Curie-Weiss law was observed that mechanical activation increases the degree of diffusion while, using a Vogel-Fulcher relationship, was confirmed reduction in the degree of relaxation of phase transition..

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

Radni status i drugi prediktori mentalnog zdravlja i kognitivnih funkcija starijih radnika u Hrvatskoj

The aim of this study was to examine mental health and cognitive functions in older Croatian workers (50–65 years) taking into account their employment status, self-assessed health, and a set of demographic characteristics. We analysed the data collected on 650 older workers (71 % employed) in the Wave 6 of the Survey of Health, Ageing and Retirement in Europe (SHARE). Unemployed workers reported symptoms of loneliness more often than the employed, while in rural areas unemployment was additionally associated with more pronounced symptoms of depression. Feeling of loneliness was also higher in those living without a partner in the household and in those with poorer health. In urban residents symptoms of depression were more severe in women, respondents with higher education, those living without a partner, and those who rated their health as poorer. As for cognitive functions, unemployment significantly predicted poorer subtraction in the rural subsample. Women in general showed less efficient numerical abilities. In the urban subsample poorer numerical abilities were also associated with lower education and living without a partner in the household. Better verbal recall was predicted by higher education and better self-rated memory. Higher scores in verbal fluency were predicted by urban residency and better self-rated health. Our results indicate that the protective factors for good mental health and cognitive functioning in older Croatian workers are being employed, having more education, living with a partner in the household, and being healthier. These findings stress the importance of implementing broader social policy strategies covering employment, education, and health.Cilj ovog rada bio je ispitati mentalno zdravlje i kognitivne funkcije starijih radnika u Hrvatskoj (50–65 godina), uzimajući u obzir njihov radni status, samoprocjenu zdravlja i skupinu demografskih karakteristika. Analizirani su podaci o 650 starijih radnika (71 % zaposlenih) iz šestog vala Istraživanja o zdravlju, starenju i umirovljenju u Europi (SHARE). Nezaposleni stariji radnici značajno su češće navodili simptome usamljenosti nego zaposleni, a u sudionika iz ruralnih područja nezaposlenost je dodatno bila povezana s izraženijim simptomima depresivnosti. Osjećaj usamljenosti također je bio izraženiji u onih koji žive bez partnera u istom domaćinstvu i onih slabijeg zdravlja. Kad je riječ o sudionicima koji žive u gradu, simptomi depresivnosti bili su izraženiji u žena, u onih koji imaju više obrazovanje, u onih koji žive bez partnera i u onih koji svoje zdravlje procjenjuju lošijim. Što se tiče kognitivnih funkcija, nezaposlenost je bila značajni prediktor lošijeg rezultata na zadacima oduzimanja u ruralnom poduzorku. Žene su općenito pokazale slabije numeričke sposobnosti. U gradskom poduzorku slabije numeričke sposobnosti bile su također povezane s nižom razinom obrazovanja i životom bez partnera u domaćinstvu. Bolje verbalno dosjećanje bilo je povezano s boljim obrazovanjem i boljom samoprocjenom pamćenja. Prediktori boljih rezultata na testu verbalne fluentnosti bili su stanovanje u gradu i bolja samoprocjena zdravlja. Naši rezultati pokazuju da su zaposlenost, bolje obrazovanje, život s partnerom i bolje zdravstveno stanje protektivni faktori mentalnog zdravlja i kognitivnog funkcioniranja starijih radnika u Hrvatskoj

La-doped and La/Mn-co-doped Barium Titanate Ceramics

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 modified polymeric precursor method based on the Pechini process. The ceramics were obtained by sintering at 1300 degrees C for 8 h. The influence of dopants on structural changes and grain size reduction was analyzed. The presence of dopants influenced 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 diffuseness of phase transitions indicating the formation of a diffuse ferroelectric material but in the co-doped ceramics the phase transition diffuseness decreased. The resistivity of the co-doped ceramics was higher than for lanthanum doped ceramics, indicating possible segregation of manganese at grain boundaries that influenced the total resistivity of the material

Ličnost i samoprocjena fizičkoga i emocionalnoga zdravlja u studenata prve godine fakulteta

The aim of this study was to determine the four personality traits: psychoticism (P), extraversion (E), neuroticism (N) and lie tendencies (L) measured by the Eysenck Personality Questionnaire, depression symptoms measured by the Zung Depression Scale (ZDS) and self-perceived health-related well- -being measured by SF-36 in a sample of 430 healthy first-year university students of both sexes. We also wanted to determine which personality variable best predicts depression symptoms (ZDS) and well-being (SF-36). The obtained results showed that students rated their health and health-related quality of life as good, although they scored lower than same aged adults from the general population. Women had significantly higher scores on ZDS, N and L than men, while men scored higher on P and six out of eight SF-36 scales. N, among all of the other included personality variables, best predicts depression symptoms on ZDS and self-perceived physical and emotional health on SF-36. We also found that gender was not a moderator in any of the personality traits in their influence on well-being, but that N in females only adds significantly to the expression of depression symptoms. We concluded that personality plays an important role in subjective health-related well-being together with objective life circumstances.Cilj ove studije bio je odrediti četiri osobine ličnosti: psihoticizam (P), ekstraverziju (E), neuroticizam (N) i tendenciju laganju (L) primjenom Eysenckova upitnika ličnosti, depresivnih simptoma primjenom Zungove skale depresije (ZDS) te samoprocjenu osjećaja dobrobiti primjenom upitnika SF-36 na uzorku od 430 zdravih studenata prve godine fakulteta obaju spolova. Željeli smo ispitati i koja varijabla ličnosti najbolje predviđa simptome depresije (ZDS) i osjećaj dobrobiti (SF-36). Rezultati su pokazali kako su studenti procijenili svoje zdravlje i kvalitetu života vezanu za zdravlje kao dobre, iako su njihove samoprocjene lošije od skupine iste dobi iz opće populacije. Žene su postigle značajno više rezultate na ZDS, N i L nego muškarci, a muškarci na P i šest od osam skala SF-36. Među svim uključenim varijablama ličnosti N najbolje predviđa depresivne simptome na ZDS kao i samoprocijenjeno fizičko i emocionalno zdravlje na SF-36. Našli smo i kako spol nije moderator crta ličnosti u njihovu utjecaju na osjećaj dobrobiti, ali kako N samo u žena značajno utječe na povećanu ekspresiju depresivnih simptoma. Zaključili smo da ličnost uz objektivne okolnosti ima važnu ulogu u subjektivnoj procjeni dobrobiti vezanoj uz zdravlje

Barium titanate thick films prepared by screen printing technique

The barium titanate (BaTiO3) thick films were prepared by screen printing technique using powders obtained by soft chemical route, modified Pechini process. Three different barium titanate powders were prepared: i) pure, ii) doped with lanthanum and iii) doped with antimony. Pastes for screen printing were prepared using previously obtained powders. The thick films were deposited onto Al2O3 substrates and fired at 850°C together with electrode material (silver/palladium) in the moving belt furnace in the air atmosphere. Measurements of thickness and roughness of barium titanate thick films were performed. The electrical properties of thick films such as dielectric constant, dielectric losses, Curie temperature, hysteresis loop were reported. The influence of different factors on electrical properties values was analyzed

Study of Barium Bismuth Titanate Prepared by Mechanochemical Synthesis

Barium-bismuth titanate, BaBi4Ti4O15 (BBT), a member of Aurivillius bismuth-based layer-structure perovskites, was prepared from stoichiometric amounts of barium titanate and bismuth titanate obtained via mechanochemical synthesis. Mechanochemical synthesis was performed in air atmosphere in a planetary ball mill. The reaction mechanism of BaBi4Ti4O15 and the preparation and characteristics of BBT ceramic powders were studied using XRD, Raman spectroscopy, particle analysis and SEM. The Bi-layered perovskite structure Of BaBi4Ti4O15 ceramic forms at 1100 degrees C for 4 h without a pre-calcination step. The microstructure of BaBi4Ti4O15 exhibits plate-like grains typical for the Bi-layered structured material and spherical and polygonal grains. The Ba2+ addition leads to changes in the microstructure development, particularly in the change of the average grain size

Examination of the antimalarial potential of experimental aminoquinolines: poor in vitro effect does not preclude in vivo efficacy

Malaria remains a major disease in the developing world and globally is the most important parasitic disease causing significant morbidity and mortality. Because of widespread resistance to conventional antimalarials, including chloroquine (CQ), new drugs are urgently needed. Here we report on the antimalarial efficacy, both in vitro and in vivo, of a series of aminoquinoline derivatives with adamantane or benzothiophene as a carrier. In vitro efficacy was evaluated by a lactate dehydrogenase (LDH) assay in cultures of a CQ-sensitive (3D7) and CQ-resistant (Dd2) strain of Plasmodium falcipanim. Of a series of 26 screened compounds, 12 that exerted a growth inhibition rate of gt = 5% were further examined in vitro to determine the 50% inhibitory concentration (IC50) values. Nine compounds shown in preliminary experiments to be non-toxic in vivo were evaluated in C57BL/6 mice infected with Plasmodium herghei ANKA strain using a modified Thompson test. All nine compounds examined in vivo prolonged the survival of treated versus untreated mice, four of which afforded gt = 60% survival. Most notably, two of these compounds, both with the adamantane carrier, afforded complete cure (100% survival and parasite clearance). Interestingly, one of these compounds had no in vitro effect against the CQ resistant P. falciparum strain. Better in vivo compared with in vitro results suggest a role for compound metabolites rather than the compounds themselves. The results presented here point to adamantane as a carrier that enhances the antimalarial potential of aminoquinolines

CHARACTERIZATION OF BARIUM BISMUTH TITANATE OBTAINED BY MECHANOCHEMICAL SYNTHESIS

Barium bismuth titanate, BaBi4Ti4O15 (BBT) was prepared by homogenization and sintering of mixture of stoichiometric quantities of BaTiO3 and Bi4Ti3O12 obtained via mechanochemical synthesis. The reaction mechanism of BaBi4Ti4O15 formation and the characteristics of BBT powders and ceramics were studied using XRD, Raman spectroscopy and SEM. The results confirmed that BaBi4Ti4O15 was formed by tetragonal symmetry. Only 4 Raman modes are clearly observed. Ba2+ ions randomly occupy the Bi sites of a pseudo-perovskite layer and may enter in a bismuth oxide layer. BaBi4Ti4O15 ceramics possess the plate-like structure typical for layered structure materials

INFLUENCE OF DOPING ION VALENCE AND SIZE ON PROPERTIES OF BiFeO3 MATERIALS

Bismuth ferrite (BiFeO3) is one of the most promising single multiferroic materials, and for sure the most studied one. It expresses specific magnetic and electric properties well above the room temperature. However, the nature of its properties is still arguable. In this study, an attempt to reveal some of the peculiarities of BiFeO3 by introducing metal ions of various valences and sizes in the places of Bi3+ and Fe3+ ions. Powders with 5 mol% of doping metals were synthesized by auto-combustion method using glycine as a fuel. The powders and ceramic samples prepared from them were characterized. At this level, doping ions make significant change in structure, phase composition, rate of the solid state reaction, microstructure, conductivity, electrical polarization and magnetization. Potential mechanisms of their influence on different properties are discussed