The diffuse phase transition of Ti-rich (Ba0.75Sr0.25) Ti1+dO3+2d dielectric ceramics

Abstract

The microstructures, dielectric properties and phase-transition behavior of Ti-rich barium-strontium-titanate-based ceramics synthesized by the solid-state method were investigated with a non-stoichiometric level by SEM, XRD and an LCR measuring system. It was found that all the (Ba0.75Sr0.25)Ti1+dO3+2d ceramics (d = 0.005, 0.01, 0.015, 0.02) are single-phase solid solutions with a typical tetragonal perovskite structure. With an increasing d value, the average grain size of the (Ba0.75Sr0.25)Ti1+dO3+2d ceramics increases. The strengthened spontaneous polarization resulting from the unit-cell deformation is responsible for the increase of the transition temperature Tm as d increases. Also, the dielectric parameters erRT and em increase with an increasing non-stoichiometric level. The low-temperature (T £ Tm) frequency dispersion of the relative dielectric constant can be found and the diffuse phase-transition behavior is suppressed with an increasing d value in the (Ba0.75Sr0.25)Ti1+dO3+2d ceramics.Avtorji so analizirali mikrostrukture, dielektri~ne lastnosti in fazne prehode barij-stroncij titanatne kermamike bogate s Ti, ki so jo sintetizirali z metodo sintranja v trdni fazi. Analize na nestehiometri~nem nivoju so izvajali s pomo~jo SEM, XRD in LCR preiskovalnih sistemov. Ugotovili so da vsebuje (Ba0.75Sr0.25)Ti1+dO3+2d keramika (pri d = 0,005, 0,01, 0,015 ali 0,02) enofazno trdno raztopino s tipi~no tetragonalno peroviskitno strukturo. Z nara{~ajo~o vrednostjo d nara{~a povpre~na velikost kristalnih zrn (Ba0.75Sr0.25)Ti1+dO3+2d keramike. Oja~ana spontana polarizacija je posledica deformacije enovite celice, kar povzro~i z nara{~ajo~im d tudi nara{~anje temperature prehoda Tm. Prav tako s pove~evanjem nestehiometrije nara{~ata dielektri~na parametra erRT in em. Ugotovili so tudi, da ima z nara{~ajo~o vrednostjo d (Ba0.75Sr0.25)Ti1+dO3+2d keramika nizko disperzijo temperaturne frekvence (T = Tm) relativne dielektri~ne konstante in zatrt prehod difuzivne faze. Klju~ne