Growth and dielectric properties of congruently melting Ba1-xCaxTiO3 crystals

The phase diagram of the system BaTiO3-CaTiO3 is investigated with regard to a congruently melting composition. The liquidus curve is determined from x = 0.0 to 0.3, where x is the mole fraction of CaTiO3. It shows a minimum melting point near x = 0.23. Ba1-xCaxTiO3 crystals are grown by the Czochralski technique from melts close to this composition. X-ray fluorescence analyses of the crystals indicate a congruently melting composition at x = 0.227, corresponding to the observed minimum melting point. At the growth temperature the crystals possess a cubic perovskite-type structure. They undergo a structure change to the ferroelectric tetragonal phase at 98 +/- 3 degrees C, indicated by a sharp peak of the dielectric constant. Down to -120 degrees C no further phase transition is observed.