Synthesis and physical properties of single crystals and ceramics of new ferroelectric BaTi2O5

Single crystals of ferroelectric BaTi2O5 were grown by a floating zone method, and the dielectric constant and specific heat were measured in a temperature range of 300-800 K. The dielectric constant and dielectric loss along the b-axis show a large dielectric dispersion at T-C = 730 K, similar to the ferroelectric phase transition of the order-disorder type. Transition enthalpy and transition entropy were estimated to be Delta H = 98.6 J/mol and Delta S = 0.136 J/molK, respectively. The optical absorption edge of the crystals exists near 365 rim. Single-phase BaTi2O5 powder was successfully synthesized through a sol-gel route, using barium diethoxide and titanium tetraisopropoxide, and the porous ceramics sintered at 1375 K show a broad maximum in the electrical capacitance vs T curve at approximately 600 K.