The electrical properties of ferroelectric LiTaO3 and its solid solutions

ac impedance techniques have been used to characterize ceramic samples of LiTaO3 and the solid solutions Li1−5xTa1+xO3 as a function of temperature in the range 350–800 °C. LiTaO3 has a low conductivity and the principal charge carriers appear to be electrons. At temperatures well removed from its ferroelectric Curie temperature, TC, 640 °C, a single arc or semicircle appears in the complex impedance plane representation of the ac impedance data and is attributed to the electronic resistance of the sample in parallel with the geometric capacitance. At temperatures close to TC an additional semicircle appears. This is attributed to a circuit element that includes the high capacitance values associated with the ferroelectric polarization processes. A method for extracting capacitance values from such data is given. It is shown that, under certain circumstances, fixed frequency measurements of capacitance can give rise to incorrect estimates of both TC and the magnitude of the capacitance as a function of temperature. The nonstoichiometric lithium tantalates are essentially lithium-ion vacancy conductors and the level of their conductivity may be correlated with composition and the solid solution mechanism. These materials are also ferroelectric and TC decreases with increasing departure from the stoichiometric composition.