For such a composition it is possible to give rough estimate of the liquidus temperature on the basis of visual-polythermal measurements, which were carried out in the 1960s by Bergman's group . If we refer to the ternary diagram in which the vertices of the composition triangle correspond to binary equimolar mixtures with a common cation (see Fig. ), we can see that the liquidus temperature in its central part (near the intersection of the bisectors) is in the vicinity of 650 o C. We emphasize that such a mixture is not eutectic, for which the liquidus and solidus temperatures coincide.