Mn-Doped BaO–(Nd0.7,Sm0.3)2O3–4TiO2 Ceramic Sintered in a Reducing Atmosphere

Abstract

The effect of MnCO3 doping from 0 to 55 mol % into BaO–(Nd0.7Sm0.3)2O3–4TiO2 (BNST) sintered in a reducing atmosphere on the phase transformation, microstructure and electrical properties was studied. The variation of d-spacing with Mn content can be divided into three regimes in this study. In regime (I), 0 to 5 mol % Mn-doped BNST, the d-spacing decreases successively until 5 mol % which is the maximum solubility, because Mn+3 is incorporated into Ti+4-sites of BNST. In regime (II), 5 to 42 mol % Mn-doped BNST, the d-spacing remains constant and Mn2O3 is precipitated because the amount of MnCO3 doped is more than the solubility. In regime (III), 43 to 55 mol % Mn-doped BNST, the d-spacing is the same as BNST without MnCO3 doping. Heavily doping MnCO3 into BNST gives rise to two parallel reactions, forming two ternary systems, BaO–(Nd,Sm)2O3–TiO2 and BaO–(Nd,Sm)2O3–Mn2O3. Mn-doped BNST sintered in a reducing atmosphere is in a semiconducing state in regimes (I) and (II), because the concentration of free electron is higher than that of the acceptors. In contrast, Mn-doped BNST in regime (III) sintered in a reducing atmosphere is in an insulating state because the concentration of the acceptors is higher than that of liberated free electron.