Single crystal growth of the tetragonal tungsten bronze CaxBa1−xNb2O6 (x=0.28; CBN-28)

The material group of the tetragonal tungsten bronzes (TTBs) is very attractive due to its outstanding ferroelectric properties. Herein we report attempts to grow single crystals of calcium barium niobate (CBN) that until now was only known as ceramic samples. The single crystal growth of CBN could be realized in two different ways. In a first step a high-temperature tetraborate flux was applied to prepare small crystals for phase analysis. Then, for the first time large single crystals of Ca0.28Ba0.72Nb2O6 (CBN-28) with dimensions up to 5 cm length were grown by using the Czochralski method. CBN-28 shows a ferroelectric phase transition at about 280°C (detected by dielectric and thermal expansion measurements) that is about 200°C higher than the transition temperature of the widely investigated TTB Sr0.60Ba0.40Nb2O6 (SBN-60).