Properties of Hexagonal Ba(Ti1-xMnx)O3 Ceramics: Effects of Sintering Temperature and Mn Content

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The effects of sintering conditions on the densification, microstructural evolution and microwave properties of Ba(Ti1-xMnx)O3 ceramics were investigated in this study. For $x\leqq 0.25$, densification is achieved at a temperature as low as 1250 °C. For $x> 0.25$, a significant densification starts only at temperatures above 1350 °C, owing to the existence of a Ba2Ti5O12 phase. X-ray photoelectron spectroscopy results manifest a change in the chemical state of Mn from Mn2+ to Mn4+ when the Mn content in the Ba(Ti1-xMnx)O3 ceramics is increased. A $\approx 0.9$ wt % weight gain is obtained when Ba(Ti0.85Mn0.15)O3 powder is heated to 1500 °C, presumably owing to the transformation of Ba(Ti0.85Mn0.15)O2.85 to Ba(Ti0.85Mn0.15)O3, associated with the conversion of Mn2+ to Mn4+ as temperature increases. The microstructural evolution and microwave dielectric properties of the Ba(Ti1-xMnx)O3 ceramics are also affected by sintering temperature and Mn content. For Ba(Ti0.85Mn0.15)O3 ceramics, as a typical example, $\varepsilon_{\text{r}}$ varies from 52 to 60 and $Q\cdot f_{\text{r}}$ changes from 2,000 to 12,000 as sintering temperature increases from 1200 to 1500 °C. However, $\tau_{\text{f}}$ ranges from 200 to 250 ppm/°C, which is independent of sintering temperature.
2007-05-15