Barreiras de potencial mapeadas por microscopia de força atômica em cerâmicas à base de BaTiO3 dopadas com lantânio Potential barriers mapping by atomic force microscopy in lanthanum doped BaTiO3 based ceramics

Cerâmicas à base de titanato de bário (BaTiO3) dopadas com 0,4% em mol de La e 150 ppm de Mn foram investigadas por microscopia de força atômica no modo de monitoramento de gradientes de campo elétrico, denominado microscopia de força elétrica, para revelar as barreiras de potencial nos contornos de grão. Estas barreiras elétricas são associadas com o abrupto aumento na resistividade elétrica que ocorre a partir da temperatura de transição ferroelétrica- paraelétrica em BaTiO3 dopado com pequenas quantidades de doadores. Mostramos que para a composição utilizada neste estudo a largura das barreiras elétricas é da ordem de 350 nm-400 nm, presentes nos contornos de grãos de tamanho médio de 1&micro;m.<br>Barium titanate (BaTiO3) based ceramics doped with La as donor (0.4at%t) and Mn as acceptor (150 ppm) were investigated through atomic force microscopy operating in electric force microscopy mode in order to reveal the potential barriers at grain boundaries. These barriers are associated with the steep rise in the resistivity above the ferroelectric-paraelectric phase transition temperature in BaTiO3 doped with small amounts of donor impurities. We show here that for such a composition the potential barrier width are of the order of 350-400 nm, present at grain boundaries of grains with size around 1 &micro;m

Effect of a BaO-CuO-Bi2O3-B2O3 glass flux, and its processing on the dielectric properties of BaTiO3

A seriesofBaTiO3 along withvarious flux oxideshasbeensinteredstep-wiselytoyieldalowsinteringtemperature flux glasscomposition. The developedglass flux (Ba-Cu-Bi-Bsystem)wasaddedtoBaTiO3 with differentamount,andeventuallyyieldedalowsinteringtemperatureof BaTiO3 at 900 1C with7wt% flux glassaddition.Toinvestigatetheinfluence ofprocessingmethods,a flux glassshell-BaTiO3 core structure was developedbyusingseparateballmillingscheduleofglassandbariumtitanatepowders.Comparisonofresultantdielectricpropertieswas made amongdifferentprocessingmethods,andthis flux shellprocessingmethodsnotablymodifies thedielectricpropertiesofsinteredsamples comparing toconventionalprocessingmethods.Thesubsequentstructuralinformation,morphology,andphasestabilityofsinteredsampleswere investigated byInfraredspectroscopy,X-rayphotoelectronspectroscopy(XPS),scanningelectronmicroscopy(SEM)andX-raydiffraction (XRD) respectively.93wt%BaTiO3-7 wt%glasswiththe flux shellstructuredisplayedaninhibitedcubicphasegraingrowth,andareduced tetragonality associatedwithCudopingwasconfirmed byX-raydiffraction.Ahighdielectricconstant(43000) aswellasalowlossyfactor (o0.03) ofthisparticularseriesofsamplewasreported.X-rayphotoelectronspectroscopyshowedthatbridgingoxygenspeciesdecreaseswith increasing Ndaddition,indicatingthattheNdbondstotheglassnetworkasanetworkmodifier insteadofbeingdopedintoBaTiO3 lattice through the flux shell.Thus,weconcludedthattheglass flux shellplaystheroleofsinteringadditive,Cudopingion(containedinglass)carrier, and Ndaliendopantblock