Ho2O3 additive effects on BaTiO3 ceramics microstructure and dielectric properties

Abstract

Dopirana BaTiO3 keramika je našla veliku primenu za dobijanje PTCR otpornika, višeslojnih keramičkih kondenzatora i temperaturnih senzora. U radu ispitivane su mikrostrukturne i dielektrične karakteristike Ho dopirane BaTiO3 keramike. Koncentracija aditiva, Ho2O3, kretala se od 0.01 do 1.0wt%. Uzorci dopirane BaTiO3 keramike dobijeni su konvencionalnom metodom sinterivanja u čvrstoj fazi i sinterovani na 1320°C i 1380°C u trajanju od 4h. Veličina zrna i mikrostrukturne karakteristike različitih uzoraka kao i njihov fazni sastav ispitivani su SEM i EDS analizom. SEM analiza Ho/BaTiO3 dopirane keramike pokazala je da je za uzorke dopirane nižom koncentracijom aditiva karakteristična homogena mikrostruktura sa veličinom zrna od 20-30μm. Za uzorke dopirane višom koncentracijom aditiva karakteristična veličina zrna kretala se od 2-10μm. Dielektrične karakteristike merene su u temperaturnom intervalu 20-180°C. Za uzorke dopirane niskom koncentracijom aditiva (0.01 wt%) i sinterovane na 1380°C karakteristična je visoka vrednost dielektrične konstante (ε r=2400) na sobnoj temperaturi. Relativno mala promena dielektrične konstante sa temperaturom karakteristična je za uzorke dopirane visokom koncentracijom aditiva. Korišćenjem Kiri-Vajsovog i modifikovanog Kiri-Vajsovog zakona izračunati se Kirijeva konstanta (S), Kirijeva temperatura (Tc) i kritični eksponent nelinearnosti (γ). Dobijeni rezultati za γ pokazuju da je za sve ispitivane uzorke karakterističan oštar fazni prelaz.

Doped BaTiO3-ceramics is very interesting for their application as PTCR resistors, multilayer ceramic capacitors, thermal sensors etc. Ho doped BaTiO3 ceramics, with different Ho2O3 content, ranging from 0.01 to 1.0 wt% Ho, were investigated regarding their microstructural and dielectric characteristics. The samples were prepared by the conventional solid state reaction and sintered at 1320° and 1380°C in an air atmosphere for 4 hours. The grain size and microstructure characteristics for various samples and their phase composition was carried out using a scanning electron microscope (SEM) equipped with EDS system. SEM analysis of Ho/BaTiO3 doped ceramics showed that in samples doped with a rare-earth ions low level, the grain size ranged from 20-30μm, while with the higher dopant concentration the abnormal grain growth is inhibited and the grain size ranged between 2- 10μm. Dielectric measurements were carried out as a function of temperature up to 180°C. The low doped samples sintered at 1380°C, display the high value of dielectric permittivity at room temperature, 2400 for 0.01Ho/BaTiO3. A nearly flat permittivity-response was obtained in specimens with higher additive content. Using a Curie-Weiss low and modified Curie-Weiss low the Curie constant (C), Curie temperature (Tc) and a critical exponent of nonlinearity (γ) were calculated. The obtained value of γ pointed out that the specimens have almost sharp phase transition.