It is the maximum temperature at which a material will have a useful figure of merit. This temperature is limited by the melting point or chemical stability (Volatility) of material, the solubility limits of doping material; the onset of intrinsicity; and anamolous thermal diffusion caused by radiative effects, ambipolar diffusion or excition conduction.

Very little can be done, fundamentally, about the melting temperature of useful material unless a dopant which is useful for adjusting the charge carrier concentration increases melting point.

Dear Fayaz, in the case you briefly described you can control volatility by doping, but indirectly - if your dopants allow you to process your material at a lower temperature, or for a decreased time the material spends at elevated temperatures, then yes, dopants can help. You may also find the following article useful - it has been published today in the Journal of the American Ceramic Society: "Screening Sintering Aids for (K0.5Na0.5)NbO3 Ceramics" by Kepi Chen et al. Kind Regards, Paul.

Very nice answers I got from you both. Thanks. Dear Paul, thank you so much for referring latest paper. Adding to this information, I am thinking if we increase the window of solidus and liquidus line by adding dopants, in result volatility can be suppressed; but I don't know which elements' combination will play this role. As from my little experience, on other hand adding more impurities can increase volatility in terms of weight loss, though we can get good sintered material.