Microwave dielectric properties of Mn-doped BaO-(Nd0.7,Sm0.3)2O3-4TiO2 ceramic sintered in a reducing atmosphere

The effect of MnCO3 doped from 0 to 55 mol% into BaO-(Nd0.7Sm0.3)(2)O-3-4TiO(2) (BNST) sintered in a reducing atmosphere on the microstructure and electrical properties was studied. Mn3+ completely substituted into Ti4+-sites of BNST to form a solid solution, so there is no second phase until 42 mol% which is the maximum solubility. Mn (<42 mol%)-doped BNST sintered in a reducing atmosphere is in a semiconducing state because the concentration of free electron is higher than that of the acceptors. On the other hand, when Mn content doped into BNST exceeds a critical value (>43 mol%), the second Mn-rich phase due to excess of Mn3+ substituted into Ti4+-site, corresponding to original BaO-(Nd0.7Sm0.3)(2)O-3-4TiO(2) (1 1 4) phase, is formed. Mn (>43 mol%)-doped BNST sintered in a reducing atmosphere is in an insulating state because the concentration of the acceptors is higher than that of liberated free electron, so the insulation resistance becomes high and tan delta becomes low. The formation of the second Mn-rich phase affects Q x f factor and temperature coefficient of capacitance (T.C.C.) of BNST significantly. (C) 2009 Elsevier Ltd and Techna Group S.r.l. All rights reserved.