Mn-doped BaO-(Nd_0.7,Sm_0.3)₂O ₃-4TiO₂ ceramic sintered in a reducing atmosphere

The effect of MnCO₃ doping from 0 to 55 mol % into BaP-(Nd _0.7Sm_0.3)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)₂O ₃-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.