Role of Ca doping and process variables in the dielectric properties of Barium Titanate Ceramics

Abstract

Effects of Ca doping, ~alc;nation and sintet'ing teml'cTJlme on the dielectric propertlcs of BaTiO) b",ed eemmi~ weI e stmhcd in this th~,,,s Convcntional mi"ed oxide melhod was u,ed to prepare disc shape ,anlp!c. The three dOplllg levels "ere 0.05, 0 08 "nd 0.12 mole fraction of Ca substituting lla. Regardless tll~ stoichiomelry or sllltering pammeters, lhe fi[';t set of ,amples cxhihited the Curie kmperatlll'G (T,) at 55°C, much lower th~n 120"C - th~ usual Ic"nsition tempcraturc oj" Ba riO" Inslcad of ,h"rp pcol, tiley CXhlbited bell :shaped hump at 55"(. Thcse allC>nULlie, W~n; due to 11"Onpickup during milling: with sled ball, in water media. ror verification, anothcr tWObatche, of ,ample, were prepared following identic"1 powde, proce,<>ing tcchl1lqne, One boteh "al prepared using BUET precursor powder and another li'om I\IILC >ource, Thc later One was 1l00mai BaT,OJ but the other on~ did llot even simeT lo 75'((, of theorGtical den,ily. ']'i02 and B~COJ u,ed at BUET S~ern 10 COl1lamimpunlies and d~trimel\l,,1 phases, In general the die1cclric comlant (k') was bellcr for denser samples and so "a, tangent loss, Density S~elm to be a conjugcate t'C,ult of CJ1clllalion and sintcring Incomplete calcination, Or lllcomplctc reaCllOl1, leads to the formatl()n 01 ga, or blowhole during ,intering and most importantly de,ircd properrLC" not l'eah.oed owing; to nOnformation (01' pamal fOfmatlOn) of required phas,,{ '1, Due to sluggi,h nature of ,olid-Slate leaetion, calcinallon at 11OO"Cfot 7 hOllis seem, to bc o~li,factor), Sinlcring temperature and timing; ShOllld be tuned to achie\'c abO\lt 95% of theorelical density. Properly c~lcilled un-doped IhTiOJ can be sintered at 1325°C for 4 ilour, to achieve that go,,1. It was oh,erved th"t Ca did un as ~ sintering aId for doping level of O,O~ mole fraction and" bove. Dcnsitic, of doped .,an'pte did folio" a non-lineal' rciation,hip "ilh doplllg; concetllmlion and the change Ove, wu, ob,ervcd al 0.07 mole fraction. Th;s effect "a, obseTved ill'csp~~live of&inkring thcmml profile. Iron inc1u,ion in s~mples turned the eXJl~cted normal ferl'Ociectric ceramic into relaxor type, with peak k' nearly 4000. In conjunellon with Ca dopmg the Tc was shilled 10 55°C winch: with the increase ofCa dopmg level above 0,08 mole ti~~tlOn ,hined the T~ to 90'C. The k' also changcd non-tine~rly ,,,ith the Ca concentralion kvel From the XRD eMmlnatlOn, it wa, seen thntlhe extonl oftellagOllnt distQrtion "ns lh" govctnmg faclor fixing lho r,. Also observed" prefert"lxl or;elltatlon of i0021 planc at lh~ ~llIfacc of dllring: ,i ntcring. contl'ibuting to increase k' nCar CtColld beYOl]d,